acorde_core/model/

score.rs

use super::{
    duration::Duration,
    notation::{
        AccidentalDisplay, Articulation, Barline, BeamState, ChordDefinition, ChordSymbol, Clef,
        CrossStaff, Dynamic, FiguredBassFigure, GuitarTechnique, HairpinKind, KeySignature, Lyric,
        NoteHead, OttavaKind, StyledText, TabPosition, TablatureConfig, TimeSignature, TupletInfo,
        VerseLyric,
    },
    pitch::Pitch,
};
use crate::Error;
use serde::{Deserialize, Serialize};
use uuid::Uuid;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ScoreMetadata {
    pub title: String,
    pub composer: String,
    pub lyricist: String,
    pub copyright: String,
    pub work_number: String,
    pub movement_title: String,
}

impl Default for ScoreMetadata {
    fn default() -> Self {
        Self {
            title: "Untitled Score".to_string(),
            composer: String::new(),
            lyricist: String::new(),
            copyright: String::new(),
            work_number: String::new(),
            movement_title: String::new(),
        }
    }
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ScoreSettings {
    pub tempo_bpm: u16,
    pub time_signature: TimeSignature,
    pub key_signature: KeySignature,
}

impl Default for ScoreSettings {
    fn default() -> Self {
        Self {
            tempo_bpm: 120,
            time_signature: TimeSignature::default(),
            key_signature: KeySignature::default(),
        }
    }
}

/// Visual connector symbol for a group of adjacent parts.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub enum PartGroupSymbol {
    Bracket, // square bracket — orchestral strings, woodwinds
    Brace,   // curly brace — piano grand staff
    Line,    // thin vertical line
}

/// Groups a range of adjacent parts with a bracket or brace for rendering.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PartGroup {
    /// Index of the first part in the group (inclusive).
    pub first_part: usize,
    /// Index of the last part in the group (inclusive).
    pub last_part: usize,
    pub symbol: PartGroupSymbol,
    /// Whether barlines are connected across all staves in the group.
    #[serde(default)]
    pub barlines_connect: bool,
}

/// Groups a range of adjacent staves within one part.
///
/// This is distinct from [`PartGroup`], which groups separate parts.  The
/// distinction matters for MEI and MuseScore sources where a piano-like part
/// can contain several staves and nested staff groups.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct StaffGroup {
    /// Index of the first staff in the group (inclusive).
    pub first_staff: usize,
    /// Index of the last staff in the group (inclusive).
    pub last_staff: usize,
    pub symbol: PartGroupSymbol,
    /// Whether barlines are connected across all staves in the group.
    #[serde(default)]
    pub barlines_connect: bool,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Score {
    pub id: String,
    /// JSON schema version. 0 when deserialized from files that predate this field.
    #[serde(default)]
    pub schema_version: u32,
    pub metadata: ScoreMetadata,
    pub settings: ScoreSettings,
    pub parts: Vec<Part>,
    #[serde(default)]
    pub part_groups: Vec<PartGroup>,
    /// Typed score-level text annotations retained independently of legacy text fields.
    #[serde(default)]
    pub texts: Vec<StyledText>,
    /// Typed score-wide style defaults. A linked view may override each property locally.
    #[serde(default)]
    pub style_overrides: Vec<ViewStyleOverride>,
    /// Typed presentation overrides attached to stable score objects rather than a renderer key.
    #[serde(default)]
    pub object_style_overrides: Vec<ObjectStyleOverride>,
    /// Reusable chord/tablature definitions imported from interchange formats.
    #[serde(default)]
    pub chord_definitions: Vec<ChordDefinition>,
    /// Typed notation spans. Legacy note-level boolean endpoints remain supported during migration.
    #[serde(default)]
    pub spanners: Vec<NotationSpanner>,
    /// Named non-destructive projections used for linked parts and alternate layouts.
    #[serde(default)]
    pub views: Vec<ScoreView>,
}

/// A stable part/staff address used by a [`ScoreView`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub struct ViewStaffRef {
    pub part: usize,
    pub staff: usize,
}

/// Whether a view presents written notation or concert pitch.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
#[serde(rename_all = "snake_case")]
pub enum ViewTranspositionPolicy {
    #[default]
    Written,
    Concert,
}

/// Layout choices which may differ for a linked part without changing musical content.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Default)]
pub struct ScoreViewLayoutOverrides {
    #[serde(default)]
    pub measures_per_row: Option<usize>,
    #[serde(default)]
    pub hidden_staves: Vec<ViewStaffRef>,
    #[serde(default)]
    pub system_breaks: Vec<usize>,
    #[serde(default)]
    pub page_breaks: Vec<usize>,
    /// Deterministic key/value style overrides interpreted by a renderer or host.
    #[serde(default)]
    pub style_overrides: Vec<(String, String)>,
    /// Typed, bounded styling values preferred over the legacy string bridge.
    #[serde(default)]
    pub typed_style_overrides: Vec<ViewStyleOverride>,
}

/// A stable view-level style property with renderer-independent units.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum ViewStyleProperty {
    StaffSpace,
    TextScale,
    AnnotationGap,
    SystemGap,
}

/// One typed style override. `StaffSpace` is a renderer scale multiplier; the remaining
/// spacing values use staff-space units, while `TextScale` is dimensionless.
#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
pub struct ViewStyleOverride {
    pub property: ViewStyleProperty,
    pub value: f32,
}

/// A stable score object to which a typed presentation override applies.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case", tag = "kind")]
pub enum ObjectStyleTarget {
    ScoreText {
        text_index: usize,
    },
    MeasureText {
        part: usize,
        staff: usize,
        measure: usize,
        text_index: usize,
    },
    Note {
        address: NoteAddr,
    },
}

/// Bounded source information retained when an object style originated in interchange.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct StyleImportProvenance {
    pub format: String,
    pub source_location: String,
}

/// A renderer-neutral typed style override attached to a score object.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct ObjectStyleOverride {
    pub target: ObjectStyleTarget,
    pub property: ViewStyleProperty,
    pub value: f32,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub provenance: Option<StyleImportProvenance>,
}

impl ScoreViewLayoutOverrides {
    /// Return the last authored override for a property, preserving deterministic source order.
    pub fn style_value(&self, property: ViewStyleProperty) -> Option<f32> {
        self.typed_style_overrides
            .iter()
            .rev()
            .find(|override_| override_.property == property)
            .map(|override_| override_.value)
    }

    /// Resolve this view's typed style overrides onto the stable default style.
    pub fn resolved_style(&self) -> ViewStyle {
        let mut style = ViewStyle::default();
        apply_style_overrides(&mut style, &self.typed_style_overrides);
        style
    }
}

fn apply_style_overrides(style: &mut ViewStyle, overrides: &[ViewStyleOverride]) {
    for override_ in overrides {
        match override_.property {
            ViewStyleProperty::StaffSpace => style.staff_space = override_.value,
            ViewStyleProperty::TextScale => style.text_scale = override_.value,
            ViewStyleProperty::AnnotationGap => style.annotation_gap = override_.value,
            ViewStyleProperty::SystemGap => style.system_gap = override_.value,
        }
    }
}

/// Renderer-independent effective style for a linked view.
///
/// `staff_space` and `text_scale` are dimensionless multipliers. Annotation and system gaps
/// use staff-space units.
#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
pub struct ViewStyle {
    pub staff_space: f32,
    pub text_scale: f32,
    pub annotation_gap: f32,
    pub system_gap: f32,
}

impl Default for ViewStyle {
    fn default() -> Self {
        Self {
            staff_space: 1.0,
            text_scale: 1.0,
            annotation_gap: 1.0,
            system_gap: 2.0,
        }
    }
}

/// A view-local staff-kind override which never changes the source score.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub struct ViewStaffKindOverride {
    pub staff: ViewStaffRef,
    pub kind: StaffKind,
}

/// A linked, non-destructive score projection.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct ScoreView {
    pub id: String,
    pub name: String,
    #[serde(default)]
    pub parts: Vec<usize>,
    #[serde(default)]
    pub transposition_policy: ViewTranspositionPolicy,
    /// Presentation kinds applied only when this view is resolved.
    #[serde(default)]
    pub staff_kind_overrides: Vec<ViewStaffKindOverride>,
    #[serde(default)]
    pub layout: ScoreViewLayoutOverrides,
}

impl ScoreView {
    /// Construct a linked part view for one source part.
    pub fn linked_part(id: impl Into<String>, name: impl Into<String>, part: usize) -> Self {
        Self {
            id: id.into(),
            name: name.into(),
            parts: vec![part],
            transposition_policy: ViewTranspositionPolicy::Written,
            staff_kind_overrides: Vec::new(),
            layout: ScoreViewLayoutOverrides::default(),
        }
    }

    /// Construct a linked part view that presents one selected staff as tablature.
    pub fn linked_tablature_staff(
        id: impl Into<String>,
        name: impl Into<String>,
        part: usize,
        staff: usize,
    ) -> Self {
        let mut view = Self::linked_part(id, name, part);
        view.staff_kind_overrides.push(ViewStaffKindOverride {
            staff: ViewStaffRef { part, staff },
            kind: StaffKind::Tablature,
        });
        view
    }

    /// Construct a linked part view that presents one selected staff as standard notation.
    pub fn linked_standard_staff(
        id: impl Into<String>,
        name: impl Into<String>,
        part: usize,
        staff: usize,
    ) -> Self {
        let mut view = Self::linked_part(id, name, part);
        view.staff_kind_overrides.push(ViewStaffKindOverride {
            staff: ViewStaffRef { part, staff },
            kind: StaffKind::Standard,
        });
        view
    }
}

/// Bounded notation span kinds with stable source identity.
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum NotationSpannerKind {
    Slur,
    Glissando,
    TrillLine,
    Pedal,
    Ottava,
    /// A dashed continuation line after a text direction ("cresc. - - -"), MusicXML
    /// `<dashes>`.
    Dashes,
}

/// A typed, potentially cross-staff notation span between two canonical note addresses.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct NotationSpanner {
    pub id: String,
    pub kind: NotationSpannerKind,
    pub start: NoteAddr,
    pub end: NoteAddr,
    #[serde(default)]
    pub number: Option<u16>,
    #[serde(default)]
    pub line_type: Option<String>,
    #[serde(default)]
    pub text: Option<String>,
    #[serde(default)]
    pub placement: Option<String>,
    #[serde(default)]
    pub ottava_size: Option<u8>,
    /// MusicXML octave-shift direction (`up` or `down`) when this is an ottava span.
    #[serde(default)]
    pub ottava_type: Option<String>,
}

impl Default for Score {
    fn default() -> Self {
        let mut part = Part::new("Piano", "Pno.");
        part.staves.push(Staff::new(Clef::Treble));
        for _ in 0..4 {
            part.staves[0].measures.push(Measure::empty(4, 4));
        }
        Self {
            id: Uuid::new_v4().to_string(),
            schema_version: 1,
            metadata: ScoreMetadata::default(),
            settings: ScoreSettings::default(),
            parts: vec![part],
            part_groups: Vec::new(),
            texts: Vec::new(),
            style_overrides: Vec::new(),
            object_style_overrides: Vec::new(),
            chord_definitions: Vec::new(),
            spanners: Vec::new(),
            views: Vec::new(),
        }
    }
}

/// Score template presets for common ensemble configurations.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub enum ScoreTemplate {
    /// Single treble-clef part (piano by default).
    Solo,
    /// One piano part with treble + bass grand staff.
    Piano,
    /// Violin I, Violin II, Viola, Cello.
    StringQuartet,
    /// Violin I, Violin II, Viola, Cello, Contrabass.
    StringOrchestra,
    /// Two trumpets, French horn, trombone, tuba.
    BrassQuintet,
}

impl Score {
    /// Duration of a physical measure on the shared playback clock. An interchange file may
    /// write an irregular length on only one staff while other parts are silent there.
    pub fn playback_measure_beats(&self, measure_index: usize) -> f64 {
        for part in &self.parts {
            for staff in &part.staves {
                if let Some(beats) = staff
                    .measures
                    .get(measure_index)
                    .and_then(|measure| measure.actual_length)
                    .and_then(|length| length.beats())
                {
                    return beats;
                }
            }
        }
        self.parts
            .iter()
            .flat_map(|part| &part.staves)
            .find(|staff| staff.measures.get(measure_index).is_some())
            .map_or_else(
                || self.settings.time_signature.total_beats(),
                |staff| staff.measure_beats(measure_index, &self.settings.time_signature),
            )
    }

    /// This score with every typed [`NotationSpanner`] also marked on its endpoint notes'
    /// legacy flags (`slur_start`/`slur_end`, `pedal_start`/`pedal_end`, …). Exporters and
    /// renderers that read only the legacy flags use it so a span authored or edited through
    /// `Score::spanners` (whose commands clear the flags) is not silently dropped. Borrowed
    /// unchanged when there is nothing to add.
    pub fn with_legacy_spanner_flags(&self) -> std::borrow::Cow<'_, Score> {
        use crate::model::notation::OttavaKind;
        let missing = |spanner: &NotationSpanner| {
            let start = self.note_at(&spanner.start);
            let end = self.note_at(&spanner.end);
            match spanner.kind {
                NotationSpannerKind::Slur => {
                    !start.is_some_and(|n| n.slur_start) || !end.is_some_and(|n| n.slur_end)
                }
                NotationSpannerKind::Glissando => {
                    !start.is_some_and(|n| n.glissando_start)
                        || !end.is_some_and(|n| n.glissando_end)
                }
                NotationSpannerKind::TrillLine => {
                    !start.is_some_and(|n| n.trill_line_start)
                        || !end.is_some_and(|n| n.trill_line_end)
                }
                NotationSpannerKind::Pedal => {
                    !start.is_some_and(|n| n.pedal_start) || !end.is_some_and(|n| n.pedal_end)
                }
                NotationSpannerKind::Ottava => {
                    !start.is_some_and(|n| n.ottava_start.is_some())
                        || !end.is_some_and(|n| n.ottava_end)
                }
                // No note flag holds dashes; consumers read the typed spanner.
                NotationSpannerKind::Dashes => false,
            }
        };
        if !self.spanners.iter().any(missing) {
            return std::borrow::Cow::Borrowed(self);
        }
        let mut score = self.clone();
        for spanner in &self.spanners {
            if let Some(note) = score.note_at_mut(&spanner.start) {
                match spanner.kind {
                    NotationSpannerKind::Slur => note.slur_start = true,
                    NotationSpannerKind::Glissando => note.glissando_start = true,
                    NotationSpannerKind::TrillLine => note.trill_line_start = true,
                    NotationSpannerKind::Pedal => note.pedal_start = true,
                    NotationSpannerKind::Ottava if note.ottava_start.is_none() => {
                        let two = spanner.ottava_size.is_some_and(|size| size >= 15);
                        // MusicXML `up` displays the notes higher: an 8vb.
                        let up = spanner.ottava_type.as_deref() == Some("up");
                        note.ottava_start = Some(match (up, two) {
                            (false, false) => OttavaKind::Va8,
                            (false, true) => OttavaKind::Ma15,
                            (true, false) => OttavaKind::Vb8,
                            (true, true) => OttavaKind::Mb15,
                        });
                    }
                    NotationSpannerKind::Ottava | NotationSpannerKind::Dashes => {}
                }
            }
            if let Some(note) = score.note_at_mut(&spanner.end) {
                match spanner.kind {
                    NotationSpannerKind::Slur => note.slur_end = true,
                    NotationSpannerKind::Glissando => note.glissando_end = true,
                    NotationSpannerKind::TrillLine => note.trill_line_end = true,
                    NotationSpannerKind::Pedal => note.pedal_end = true,
                    NotationSpannerKind::Ottava => note.ottava_end = true,
                    NotationSpannerKind::Dashes => {}
                }
            }
        }
        std::borrow::Cow::Owned(score)
    }

    fn note_at(&self, address: &NoteAddr) -> Option<&Note> {
        self.parts
            .get(address.part)?
            .staves
            .get(address.staff)?
            .measures
            .get(address.measure)?
            .voices
            .get(address.voice)?
            .get(address.note)
    }

    fn note_at_mut(&mut self, address: &NoteAddr) -> Option<&mut Note> {
        self.parts
            .get_mut(address.part)?
            .staves
            .get_mut(address.staff)?
            .measures
            .get_mut(address.measure)?
            .voices
            .get_mut(address.voice)?
            .get_mut(address.note)
    }

    /// Resolve score-wide defaults followed by the supplied view's local overrides.
    pub fn resolved_view_style(&self, layout: &ScoreViewLayoutOverrides) -> ViewStyle {
        let mut style = ViewStyle::default();
        apply_style_overrides(&mut style, &self.style_overrides);
        apply_style_overrides(&mut style, &layout.typed_style_overrides);
        style
    }

    pub fn new(
        title: &str,
        tempo_bpm: u16,
        numerator: u8,
        denominator: u8,
        fifths: i8,
        measure_count: u32,
    ) -> Self {
        let mut score = Score::default();
        score.metadata.title = title.to_string();
        score.settings.tempo_bpm = tempo_bpm;
        score.settings.time_signature = TimeSignature {
            numerator,
            denominator,
        };
        score.settings.key_signature = KeySignature {
            fifths,
            mode: "major".to_string(),
        };

        score.parts[0].staves[0].measures.clear();
        for i in 0..measure_count {
            let mut m = Measure::empty(numerator, denominator);
            m.number = i + 1;
            score.parts[0].staves[0].measures.push(m);
        }
        score
    }

    /// Create a score pre-populated with parts for the given ensemble template.
    ///
    /// Defaults: 120 BPM, 4/4, C major, 4 empty measures.
    /// Use [`NewScoreCmd`](crate::model::commands::NewScoreCmd) to override those after creation.
    pub fn template(kind: ScoreTemplate) -> Self {
        fn measures(num: u8, den: u8, count: u32) -> Vec<Measure> {
            (0..count)
                .map(|i| {
                    let mut m = Measure::empty(num, den);
                    m.number = i + 1;
                    m
                })
                .collect()
        }
        fn part(name: &str, short: &str, clef: Clef, program: u8) -> Part {
            let mut p = Part::new(name, short);
            p.midi_program = program;
            let mut s = Staff::new(clef);
            s.measures = measures(4, 4, 4);
            p.staves.push(s);
            p
        }

        let mut score = Score {
            id: uuid::Uuid::new_v4().to_string(),
            schema_version: 1,
            metadata: ScoreMetadata::default(),
            settings: ScoreSettings::default(),
            parts: Vec::new(),
            part_groups: Vec::new(),
            texts: Vec::new(),
            style_overrides: Vec::new(),
            object_style_overrides: Vec::new(),
            chord_definitions: Vec::new(),
            spanners: Vec::new(),
            views: Vec::new(),
        };

        match kind {
            ScoreTemplate::Solo => {
                score.parts.push(part("Piano", "Pno.", Clef::Treble, 0));
            }
            ScoreTemplate::Piano => {
                let mut p = Part::new("Piano", "Pno.");
                p.midi_program = 0;
                let mut treble = Staff::new(Clef::Treble);
                treble.measures = measures(4, 4, 4);
                let mut bass = Staff::new(Clef::Bass);
                bass.measures = measures(4, 4, 4);
                p.staves.push(treble);
                p.staves.push(bass);
                score.parts.push(p);
            }
            ScoreTemplate::StringQuartet => {
                score
                    .parts
                    .push(part("Violin I", "Vn. I", Clef::Treble, 40));
                score
                    .parts
                    .push(part("Violin II", "Vn. II", Clef::Treble, 40));
                score.parts.push(part("Viola", "Va.", Clef::Alto, 41));
                score.parts.push(part("Cello", "Vc.", Clef::Bass, 42));
            }
            ScoreTemplate::StringOrchestra => {
                score
                    .parts
                    .push(part("Violin I", "Vn. I", Clef::Treble, 40));
                score
                    .parts
                    .push(part("Violin II", "Vn. II", Clef::Treble, 40));
                score.parts.push(part("Viola", "Va.", Clef::Alto, 41));
                score.parts.push(part("Cello", "Vc.", Clef::Bass, 42));
                score.parts.push(part("Contrabass", "Cb.", Clef::Bass, 43));
            }
            ScoreTemplate::BrassQuintet => {
                score
                    .parts
                    .push(part("Trumpet I", "Tpt. I", Clef::Treble, 56));
                score
                    .parts
                    .push(part("Trumpet II", "Tpt. II", Clef::Treble, 56));
                score
                    .parts
                    .push(part("French Horn", "Hn.", Clef::Treble, 60));
                score.parts.push(part("Trombone", "Tbn.", Clef::Bass, 57));
                score.parts.push(part("Tuba", "Tba.", Clef::Bass, 58));
            }
        }
        score
    }

    pub fn measure_count(&self) -> usize {
        self.parts
            .first()
            .and_then(|p| p.staves.first())
            .map(|s| s.measures.len())
            .unwrap_or(0)
    }

    /// Resolve the inclusive section containing `measure_index`.
    ///
    /// A section boundary belongs to the measure where it starts. Layout breaks are
    /// intentionally ignored: they have no editor-range semantics.
    pub fn section_range(
        &self,
        measure_index: usize,
    ) -> Result<std::ops::RangeInclusive<usize>, Error> {
        let measures = self
            .parts
            .first()
            .and_then(|part| part.staves.first())
            .map(|staff| &staff.measures)
            .ok_or(Error::MeasureNotFound(measure_index))?;
        if measure_index >= measures.len() {
            return Err(Error::MeasureNotFound(measure_index));
        }
        let start = (0..=measure_index)
            .rev()
            .find(|&index| measures[index].section_break)
            .unwrap_or(0);
        let end = ((measure_index + 1)..measures.len())
            .find(|&index| measures[index].section_break)
            .map(|index| index - 1)
            .unwrap_or(measures.len() - 1);
        Ok(start..=end)
    }

    /// Aggregate statistics about the score.
    pub fn statistics(&self) -> ScoreStats {
        let measure_count = self.measure_count();
        let part_count = self.parts.len();

        // Beat accumulation via measure_sequence so repeats are counted correctly.
        let seq = measure_sequence(self);
        let total_beats: f64 = self
            .parts
            .first()
            .and_then(|p| p.staves.first())
            .map(|s| {
                seq.iter()
                    .filter_map(|&idx| s.measures.get(idx))
                    .flat_map(|m| m.voices.iter().flat_map(|v| v.iter()))
                    .map(|n| n.beats())
                    .sum()
            })
            .unwrap_or(0.0);

        let mut note_count = 0usize;
        let mut rest_count = 0usize;
        for part in &self.parts {
            for staff in &part.staves {
                for measure in &staff.measures {
                    for voice in &measure.voices {
                        for note in voice {
                            if note.is_rest {
                                rest_count += 1;
                            } else {
                                note_count += 1;
                            }
                        }
                    }
                }
            }
        }

        let bpm = self.settings.tempo_bpm as f64;
        let estimated_duration_secs = if bpm > 0.0 {
            total_beats / bpm * 60.0
        } else {
            0.0
        };

        ScoreStats {
            measure_count,
            note_count,
            rest_count,
            part_count,
            estimated_duration_secs,
        }
    }

    /// Resolve a linked view to an independent score snapshot without mutating this score.
    ///
    /// The snapshot contains only the selected parts and notation spans whose endpoints remain
    /// inside the projection. View-only layout settings are deliberately retained in the returned
    /// view list so a layout consumer can apply them without changing the source score.
    pub fn resolve_view(&self, view_id: &str) -> Result<Score, Error> {
        let view = self
            .views
            .iter()
            .find(|view| view.id == view_id)
            .ok_or_else(|| {
                Error::InvalidCommand(format!("score view '{view_id}' does not exist"))
            })?;
        let mut source_to_target = vec![None; self.parts.len()];
        let mut parts = Vec::with_capacity(view.parts.len());
        for &source_index in &view.parts {
            let source = self
                .parts
                .get(source_index)
                .ok_or(Error::PartNotFound(source_index))?;
            if source_to_target[source_index].is_some() {
                return Err(Error::InvalidCommand(format!(
                    "score view '{}' selects part {} more than once",
                    view.id, source_index
                )));
            }
            source_to_target[source_index] = Some(parts.len());
            parts.push(source.clone());
        }
        for override_ in &view.staff_kind_overrides {
            let target_part = source_to_target
                .get(override_.staff.part)
                .copied()
                .flatten()
                .ok_or_else(|| {
                    Error::InvalidCommand(
                        "view overrides a staff outside its selected parts".into(),
                    )
                })?;
            let target_staff = parts[target_part]
                .staves
                .get_mut(override_.staff.staff)
                .ok_or_else(|| {
                    Error::InvalidCommand(format!(
                        "view overrides staff {} outside part {}",
                        override_.staff.staff, override_.staff.part
                    ))
                })?;
            if override_.kind == StaffKind::Tablature && target_staff.tablature.is_none() {
                return Err(Error::InvalidCommand(
                    "tablature view requires a tablature configuration on its source staff".into(),
                ));
            }
            target_staff.presentation.kind = override_.kind;
        }
        let spanners = self
            .spanners
            .iter()
            .filter_map(|spanner| {
                let start = source_to_target
                    .get(spanner.start.part)
                    .copied()
                    .flatten()?;
                let end = source_to_target.get(spanner.end.part).copied().flatten()?;
                let mut projected = spanner.clone();
                projected.start.part = start;
                projected.end.part = end;
                Some(projected)
            })
            .collect();
        let part_groups = self
            .part_groups
            .iter()
            .filter_map(|group| {
                let first = source_to_target.get(group.first_part).copied().flatten()?;
                let last = source_to_target.get(group.last_part).copied().flatten()?;
                Some(PartGroup {
                    first_part: first,
                    last_part: last,
                    symbol: group.symbol.clone(),
                    barlines_connect: group.barlines_connect,
                })
            })
            .collect();
        let mut projected_view = view.clone();
        projected_view.parts = (0..parts.len()).collect();
        for reference in &mut projected_view.layout.hidden_staves {
            reference.part = source_to_target
                .get(reference.part)
                .copied()
                .flatten()
                .ok_or_else(|| {
                    Error::InvalidCommand("view hides a part outside its selection".into())
                })?;
        }
        for override_ in &mut projected_view.staff_kind_overrides {
            override_.staff.part = source_to_target
                .get(override_.staff.part)
                .copied()
                .flatten()
                .ok_or_else(|| {
                    Error::InvalidCommand("view overrides a staff outside its selection".into())
                })?;
        }
        Ok(Score {
            id: Uuid::new_v4().to_string(),
            schema_version: self.schema_version,
            metadata: self.metadata.clone(),
            settings: self.settings.clone(),
            parts,
            part_groups,
            texts: self.texts.clone(),
            style_overrides: self.style_overrides.clone(),
            object_style_overrides: self.object_style_overrides.clone(),
            chord_definitions: self.chord_definitions.clone(),
            spanners,
            views: vec![projected_view],
        })
    }

    /// Return a new `Score` containing only the given part.
    /// Returns `None` if `part_index` is out of range.
    pub fn extract_part(&self, part_index: usize) -> Option<Score> {
        let part = self.parts.get(part_index)?.clone();
        let spanners = self
            .spanners
            .iter()
            .filter(|spanner| spanner.start.part == part_index && spanner.end.part == part_index)
            .cloned()
            .map(|mut spanner| {
                spanner.start.part = 0;
                spanner.end.part = 0;
                spanner
            })
            .collect();
        Some(Score {
            id: Uuid::new_v4().to_string(),
            schema_version: 1,
            metadata: self.metadata.clone(),
            settings: self.settings.clone(),
            parts: vec![part],
            part_groups: Vec::new(),
            texts: self.texts.clone(),
            style_overrides: self.style_overrides.clone(),
            object_style_overrides: self.object_style_overrides.clone(),
            chord_definitions: self.chord_definitions.clone(),
            spanners,
            views: Vec::new(),
        })
    }

    /// Extract a part through the validated transformation boundary.
    pub fn extract_part_checked(&self, part_index: usize) -> Result<Score, Error> {
        if !super::validate::validate(self).is_valid() {
            return Err(Error::InvalidScore);
        }
        let extracted = self
            .extract_part(part_index)
            .ok_or(Error::PartNotFound(part_index))?;
        if !super::validate::validate(&extracted).is_valid() {
            return Err(Error::InvalidScore);
        }
        Ok(extracted)
    }

    /// Merge two scores by appending `other`'s parts to `self`'s parts.
    /// Shorter scores are padded with empty measures to match the longer one.
    /// Metadata and settings are taken from `self`.
    pub fn merge(&self, other: &Score) -> Score {
        let self_count = self.measure_count();
        let other_count = other.measure_count();
        let max_count = self_count.max(other_count);
        let ts = self.settings.time_signature.clone();

        let pad = |mut part: Part, from: usize| -> Part {
            for staff in &mut part.staves {
                for i in from..max_count {
                    let mut m = Measure::empty(ts.numerator, ts.denominator);
                    m.number = i as u32 + 1;
                    staff.measures.push(m);
                }
            }
            part
        };

        let mut parts: Vec<Part> = self
            .parts
            .iter()
            .cloned()
            .map(|p| pad(p, self_count))
            .collect();
        for p in &other.parts {
            parts.push(pad(p.clone(), other_count));
        }
        let self_part_count = self.parts.len();
        let mut spanners = self.spanners.clone();
        spanners.extend(other.spanners.iter().cloned().map(|mut spanner| {
            spanner.start.part += self_part_count;
            spanner.end.part += self_part_count;
            spanner
        }));

        Score {
            id: Uuid::new_v4().to_string(),
            schema_version: 1,
            metadata: self.metadata.clone(),
            settings: self.settings.clone(),
            parts,
            part_groups: Vec::new(),
            texts: self.texts.clone(),
            style_overrides: self.style_overrides.clone(),
            object_style_overrides: self.object_style_overrides.clone(),
            chord_definitions: self.chord_definitions.clone(),
            spanners,
            views: Vec::new(),
        }
    }

    /// Merge scores through the validated transformation boundary.
    pub fn merge_checked(&self, other: &Score) -> Result<Score, Error> {
        if !super::validate::validate(self).is_valid()
            || !super::validate::validate(other).is_valid()
        {
            return Err(Error::InvalidScore);
        }
        let merged = self.merge(other);
        if !super::validate::validate(&merged).is_valid() {
            return Err(Error::InvalidScore);
        }
        Ok(merged)
    }
}

/// Aggregate statistics returned by [`Score::statistics`].
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct ScoreStats {
    pub measure_count: usize,
    /// Number of non-rest notes across all parts.
    pub note_count: usize,
    pub rest_count: usize,
    pub part_count: usize,
    /// Rough estimate: `total_beats(first part) / tempo_bpm * 60`.
    pub estimated_duration_secs: f64,
}

// ── transpose ─────────────────────────────────────────────────────────────────

use super::pitch::Step;
use super::repeat::measure_sequence;

/// Assign deterministic guitar tablature positions to eligible notes and chords.
///
/// Existing positions are preserved. For each note, the lowest reachable fret is
/// selected, breaking ties toward the highest string (the lowest string number). For
/// chords, strings are unique and the assignment minimizes total fret, then fret
/// span, then highest fret. This is a bounded deterministic fingering heuristic,
/// not a claim of instrument-specific playability.
/// The staff tuning is interpreted as open-string MIDI pitches before capo, and
/// assignments are limited to frets 0 through 24. Rests, chords, and notes with
/// no reachable position are left unchanged. Returns the number of notes/chords
/// assigned.
pub fn assign_tablature_positions(score: &mut Score) -> usize {
    const MAX_FRET: i16 = 24;
    let mut assigned = 0;

    for part in &mut score.parts {
        for staff in &mut part.staves {
            if staff.tablature.is_none() {
                continue;
            }
            let configurations: Vec<Option<TablatureConfig>> = (0..staff.measures.len())
                .map(|measure_index| staff.tablature_at(measure_index))
                .collect();

            for (measure_index, measure) in staff.measures.iter_mut().enumerate() {
                let Some(tab) = configurations[measure_index].as_ref() else {
                    continue;
                };
                for voice in &mut measure.voices {
                    for note in voice.iter_mut() {
                        if note.is_rest
                            || note.tab_position.is_some()
                            || !note.tab_positions.is_empty()
                            || note.pitches.is_empty()
                        {
                            continue;
                        }
                        let pitches: Vec<i16> = note.pitches.iter().map(Pitch::to_midi).collect();
                        let Some(positions) = best_tablature_assignment(
                            &pitches,
                            &tab.tuning_midi,
                            tab.lines as usize,
                            i16::from(tab.capo),
                            MAX_FRET,
                        ) else {
                            continue;
                        };

                        note.tab_position = positions.first().cloned();
                        note.tab_positions = positions;
                        note.string_number = note.tab_position.as_ref().map(|p| p.string);
                        assigned += 1;
                    }
                }
            }
        }
    }

    assigned
}

/// Optimize tablature positions across each voice using bounded position movement.
///
/// Explicit positions are treated as fixed anchors. Unassigned notes and chords
/// receive positions that minimize fret load plus movement from the preceding
/// event; ties are resolved deterministically. Returns the number of notes/chords
/// newly assigned.
pub fn optimize_tablature_positions(score: &mut Score) -> usize {
    const MAX_FRET: i16 = 24;
    let mut assigned = 0;

    for part in &mut score.parts {
        for staff in &mut part.staves {
            if staff.tablature.is_none() {
                continue;
            }
            let configurations: Vec<Option<TablatureConfig>> = (0..staff.measures.len())
                .map(|measure_index| staff.tablature_at(measure_index))
                .collect();
            for voice in 0..4 {
                // Work per measure/voice location so repeated note indices remain distinct.
                let mut locations = Vec::new();
                for (measure_index, measure) in staff.measures.iter().enumerate() {
                    for (note_index, note) in measure.voices[voice].iter().enumerate() {
                        if !note.is_rest && !note.pitches.is_empty() {
                            locations.push((measure_index, note_index, note.clone()));
                        }
                    }
                }
                let candidates: Vec<Vec<Vec<TabPosition>>> = locations
                    .iter()
                    .map(|(measure_index, _, note)| {
                        if let Some(positions) = if !note.tab_positions.is_empty() {
                            Some(note.tab_positions.clone())
                        } else {
                            note.tab_position.clone().map(|position| vec![position])
                        } {
                            vec![positions]
                        } else {
                            let Some(tab) = configurations[*measure_index].as_ref() else {
                                return Vec::new();
                            };
                            tablature_assignments(
                                &note.pitches.iter().map(Pitch::to_midi).collect::<Vec<_>>(),
                                &tab.tuning_midi,
                                tab.lines as usize,
                                i16::from(tab.capo),
                                MAX_FRET,
                            )
                        }
                    })
                    .collect();
                if candidates.iter().any(Vec::is_empty) {
                    continue;
                }

                let mut costs: Vec<Vec<(u32, Option<usize>)>> = candidates
                    .iter()
                    .map(|events| vec![(u32::MAX, None); events.len()])
                    .collect();
                for (candidate_index, candidate) in candidates[0].iter().enumerate() {
                    costs[0][candidate_index] = (tablature_load(candidate), None);
                }
                for event_index in 1..candidates.len() {
                    for (candidate_index, candidate) in candidates[event_index].iter().enumerate() {
                        let load = tablature_load(candidate);
                        for (previous_index, previous) in
                            candidates[event_index - 1].iter().enumerate()
                        {
                            let previous_cost = costs[event_index - 1][previous_index].0;
                            let cost = previous_cost
                                .saturating_add(load)
                                .saturating_add(tablature_movement(previous, candidate));
                            if cost < costs[event_index][candidate_index].0 {
                                costs[event_index][candidate_index] = (cost, Some(previous_index));
                            }
                        }
                    }
                }
                let mut selected = vec![0; candidates.len()];
                if let Some((last, _)) = costs.last().and_then(|row| {
                    row.iter()
                        .enumerate()
                        .min_by_key(|(index, (cost, _))| (*cost, *index))
                }) {
                    selected[candidates.len() - 1] = last;
                    for event_index in (1..candidates.len()).rev() {
                        selected[event_index - 1] =
                            costs[event_index][selected[event_index]].1.unwrap_or(0);
                    }
                }

                for (((measure_index, note_index, original), event_candidates), selected_index) in
                    locations.into_iter().zip(candidates).zip(selected)
                {
                    if original.tab_position.is_none() && original.tab_positions.is_empty() {
                        let note = &mut staff.measures[measure_index].voices[voice][note_index];
                        let positions = event_candidates[selected_index].clone();
                        note.tab_position = positions.first().cloned();
                        note.tab_positions = positions;
                        note.string_number = note.tab_position.as_ref().map(|p| p.string);
                        assigned += 1;
                    }
                }
            }
        }
    }

    assigned
}

fn tablature_load(positions: &[TabPosition]) -> u32 {
    let sum: u32 = positions
        .iter()
        .map(|position| u32::from(position.fret))
        .sum();
    let min = positions
        .iter()
        .map(|position| position.fret)
        .min()
        .unwrap_or(0);
    let max = positions
        .iter()
        .map(|position| position.fret)
        .max()
        .unwrap_or(0);
    let span = max - min;
    // A four-fret hand position is a practical baseline; wide chords receive
    // a strong penalty so a higher but compact voicing wins when available.
    let stretch_penalty = span.saturating_sub(4) as u32 * 12;
    sum + u32::from(span) * 2 + stretch_penalty
}

fn tablature_movement(previous: &[TabPosition], current: &[TabPosition]) -> u32 {
    previous
        .iter()
        .zip(current)
        .map(|(a, b)| u32::from(a.fret.abs_diff(b.fret)) + u32::from(a.string.abs_diff(b.string)))
        .sum()
}

fn tablature_assignments(
    pitches: &[i16],
    tuning: &[i16],
    lines: usize,
    capo: i16,
    max_fret: i16,
) -> Vec<Vec<TabPosition>> {
    #[allow(clippy::too_many_arguments)]
    fn visit(
        pitches: &[i16],
        tuning: &[i16],
        lines: usize,
        capo: i16,
        max_fret: i16,
        index: usize,
        used: &mut [bool],
        current: &mut Vec<TabPosition>,
        output: &mut Vec<Vec<TabPosition>>,
    ) {
        if index == pitches.len() {
            output.push(current.clone());
            return;
        }
        for (string, open) in tuning.iter().enumerate().take(lines) {
            if used[string] {
                continue;
            }
            let fret = pitches[index] - *open - capo;
            if !(0..=max_fret).contains(&fret) {
                continue;
            }
            used[string] = true;
            current.push(TabPosition {
                string: (string + 1) as u8,
                fret: fret as u8,
            });
            visit(
                pitches,
                tuning,
                lines,
                capo,
                max_fret,
                index + 1,
                used,
                current,
                output,
            );
            current.pop();
            used[string] = false;
        }
    }

    if pitches.is_empty() || pitches.len() > lines {
        return Vec::new();
    }
    let mut output = Vec::new();
    visit(
        pitches,
        tuning,
        lines,
        capo,
        max_fret,
        0,
        &mut vec![false; lines],
        &mut Vec::new(),
        &mut output,
    );
    output
}

fn best_tablature_assignment(
    pitches: &[i16],
    tuning: &[i16],
    lines: usize,
    capo: i16,
    max_fret: i16,
) -> Option<Vec<TabPosition>> {
    type Assignment = (i16, i16, i16, Vec<u8>, Vec<TabPosition>);

    #[allow(clippy::too_many_arguments)]
    fn search(
        pitches: &[i16],
        tuning: &[i16],
        lines: usize,
        capo: i16,
        max_fret: i16,
        index: usize,
        used: &mut [bool],
        current: &mut Vec<TabPosition>,
        best: &mut Option<Assignment>,
    ) {
        if index == pitches.len() {
            let sum: i16 = current.iter().map(|p| i16::from(p.fret)).sum();
            let min = current.iter().map(|p| p.fret).min().unwrap_or(0);
            let max = current.iter().map(|p| p.fret).max().unwrap_or(0);
            let strings: Vec<u8> = current.iter().map(|p| p.string).collect();
            let candidate = (
                sum,
                i16::from(max) - i16::from(min),
                i16::from(max),
                strings,
                current.clone(),
            );
            if best.as_ref().is_none_or(|existing| {
                (candidate.0, candidate.1, candidate.2, &candidate.3)
                    < (existing.0, existing.1, existing.2, &existing.3)
            }) {
                *best = Some(candidate);
            }
            return;
        }

        for (string, open) in tuning.iter().enumerate().take(lines) {
            if used[string] {
                continue;
            }
            let fret = pitches[index] - *open - capo;
            if !(0..=max_fret).contains(&fret) {
                continue;
            }
            used[string] = true;
            current.push(TabPosition {
                string: (string + 1) as u8,
                fret: fret as u8,
            });
            search(
                pitches,
                tuning,
                lines,
                capo,
                max_fret,
                index + 1,
                used,
                current,
                best,
            );
            current.pop();
            used[string] = false;
        }
    }

    if pitches.len() > lines {
        return None;
    }
    let mut used = vec![false; lines];
    let mut current = Vec::with_capacity(pitches.len());
    let mut best = None;
    search(
        pitches,
        tuning,
        lines,
        capo,
        max_fret,
        0,
        &mut used,
        &mut current,
        &mut best,
    );
    best.map(|(_, _, _, _, positions)| positions)
}

/// Return a new `Score` with all pitches shifted by `semitones`.
/// Key signatures (global and per-measure) are updated accordingly.
/// If `semitones == 0` the score is cloned unchanged.
pub fn transpose(score: &Score, semitones: i8) -> Score {
    if semitones == 0 {
        return score.clone();
    }
    let mut out = score.clone();
    out.settings.key_signature.fifths = transpose_fifths(
        score.settings.key_signature.fifths,
        &score.settings.key_signature.mode,
        semitones,
    );
    for part in &mut out.parts {
        for staff in &mut part.staves {
            for measure in &mut staff.measures {
                if let Some(ref mut ks) = measure.key_sig {
                    ks.fifths = transpose_fifths(ks.fifths, &ks.mode, semitones);
                }
                for voice in &mut measure.voices {
                    for note in voice.iter_mut() {
                        for pitch in note.pitches.iter_mut() {
                            *pitch = transpose_pitch(pitch, semitones);
                        }
                    }
                }
            }
        }
    }
    out
}

/// Transpose a score through the validated transformation boundary.
pub fn transpose_checked(score: &Score, semitones: i8) -> Result<Score, Error> {
    if !super::validate::validate(score).is_valid() {
        return Err(Error::InvalidScore);
    }
    let transposed = transpose(score, semitones);
    if !super::validate::validate(&transposed).is_valid() {
        return Err(Error::InvalidScore);
    }
    Ok(transposed)
}

/// Choose whether a regional transposition rewrites notation or concert sounding pitch.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum RegionalTranspositionTarget {
    /// Rewrite written pitches and local key signatures in the selected measures.
    Written,
    /// Keep written notation unchanged and adjust the staff's concert-pitch offset.
    Concert,
}

/// Transpose one inclusive-start, exclusive-end staff measure range through the validated
/// transformation boundary. The source score is never mutated.
pub fn transpose_staff_region_checked(
    score: &Score,
    part_index: usize,
    staff_index: usize,
    start_measure: usize,
    end_measure: usize,
    semitones: i8,
    target: RegionalTranspositionTarget,
) -> Result<Score, Error> {
    if !super::validate::validate(score).is_valid() {
        return Err(Error::InvalidScore);
    }
    let source_staff = score
        .parts
        .get(part_index)
        .ok_or(Error::PartNotFound(part_index))?
        .staves
        .get(staff_index)
        .ok_or(Error::StaffNotFound(staff_index))?;
    if start_measure >= end_measure || end_measure > source_staff.measures.len() {
        return Err(Error::InvalidCommand(format!(
            "invalid measure range {start_measure}..{end_measure}"
        )));
    }
    if target == RegionalTranspositionTarget::Concert
        && (start_measure != 0 || end_measure != source_staff.measures.len())
    {
        return Err(Error::InvalidCommand(
            "concert-pitch staff transposition requires the full staff range".into(),
        ));
    }
    let mut transformed = score.clone();
    let staff = &mut transformed.parts[part_index].staves[staff_index];
    match target {
        RegionalTranspositionTarget::Written => {
            for measure in &mut staff.measures[start_measure..end_measure] {
                if let Some(key) = &mut measure.key_sig {
                    key.fifths = transpose_fifths(key.fifths, &key.mode, semitones);
                }
                for voice in &mut measure.voices {
                    for note in voice {
                        for pitch in &mut note.pitches {
                            *pitch = transpose_pitch(pitch, semitones);
                        }
                    }
                }
            }
        }
        RegionalTranspositionTarget::Concert => {
            staff.transpose_semitones = staff.transpose_semitones.saturating_add(semitones);
        }
    }
    if !super::validate::validate(&transformed).is_valid() {
        return Err(Error::InvalidScore);
    }
    Ok(transformed)
}

fn transpose_pitch(pitch: &Pitch, semitones: i8) -> Pitch {
    let new_midi = (pitch.to_midi() + semitones as i16).clamp(0, 127) as u8;
    let pc = new_midi % 12;
    let oct = (new_midi / 12) as i8 - 1;
    let (step, alter): (Step, i8) = if semitones >= 0 {
        match pc {
            0 => (Step::C, 0),
            1 => (Step::C, 1),
            2 => (Step::D, 0),
            3 => (Step::D, 1),
            4 => (Step::E, 0),
            5 => (Step::F, 0),
            6 => (Step::F, 1),
            7 => (Step::G, 0),
            8 => (Step::G, 1),
            9 => (Step::A, 0),
            10 => (Step::A, 1),
            11 => (Step::B, 0),
            _ => (Step::C, 0),
        }
    } else {
        match pc {
            0 => (Step::C, 0),
            1 => (Step::D, -1),
            2 => (Step::D, 0),
            3 => (Step::E, -1),
            4 => (Step::E, 0),
            5 => (Step::F, 0),
            6 => (Step::G, -1),
            7 => (Step::G, 0),
            8 => (Step::A, -1),
            9 => (Step::A, 0),
            10 => (Step::B, -1),
            11 => (Step::B, 0),
            _ => (Step::C, 0),
        }
    };
    Pitch::with_microtone(step, oct, alter, pitch.microtone_cents)
}

/// Shift a key signature's fifths value by `semitones`.
///
/// Uses the circle-of-fifths arithmetic:
/// - `tonic_pc = (fifths * 7) mod 12`  (for major; minor adds 9 to get relative major tonic)
/// - `new_fifths = (new_tonic_pc * 7) mod 12`, adjusted to `[-7, 7]`
fn transpose_fifths(fifths: i8, mode: &str, semitones: i8) -> i8 {
    let tonic_major_pc = ((fifths as i32 * 7).rem_euclid(12)) as u8;
    let tonic_pc = if mode == "minor" {
        ((tonic_major_pc as i32 + 9).rem_euclid(12)) as u8
    } else {
        tonic_major_pc
    };
    let new_tonic = ((tonic_pc as i32 + semitones as i32).rem_euclid(12)) as u8;
    let major_tonic = if mode == "minor" {
        ((new_tonic as i32 + 3).rem_euclid(12)) as u8
    } else {
        new_tonic
    };
    let raw = ((major_tonic as i32 * 7).rem_euclid(12)) as i8;
    if raw > 6 { raw - 12 } else { raw }
}

/// Inclusive MIDI note-number range declared by an instrument definition.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub struct InstrumentRange {
    pub lowest: u8,
    pub highest: u8,
}

/// Stable, renderer-independent instrument semantics for a part.
///
/// This is deliberately separate from a part's current MIDI state: the latter
/// records imported/performance values, while this definition supplies the
/// instrument identity, notation defaults, and practical written/sounding
/// ranges used by editors and layout clients.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct InstrumentDefinition {
    /// Stable source or application-defined identifier. It must be non-empty.
    pub id: String,
    #[serde(default)]
    pub name: String,
    #[serde(default)]
    pub short_name: String,
    #[serde(default)]
    pub family: Option<String>,
    #[serde(default)]
    pub transpose_semitones: i8,
    #[serde(default)]
    pub written_range: Option<InstrumentRange>,
    #[serde(default)]
    pub sounding_range: Option<InstrumentRange>,
    #[serde(default)]
    pub default_clefs: Vec<Clef>,
    #[serde(default = "default_instrument_staff_count")]
    pub staff_count: u8,
    #[serde(default)]
    pub staff_kind: StaffKind,
    #[serde(default)]
    pub midi_channel: u8,
    #[serde(default)]
    pub midi_program: u8,
    #[serde(default)]
    pub percussion_map_id: Option<String>,
}

const fn default_instrument_staff_count() -> u8 {
    1
}

impl InstrumentDefinition {
    /// Construct a minimal single-staff instrument declaration.
    pub fn new(id: impl Into<String>, name: impl Into<String>) -> Self {
        Self {
            id: id.into(),
            name: name.into(),
            short_name: String::new(),
            family: None,
            transpose_semitones: 0,
            written_range: None,
            sounding_range: None,
            default_clefs: Vec::new(),
            staff_count: 1,
            staff_kind: StaffKind::Standard,
            midi_channel: 0,
            midi_program: 0,
            percussion_map_id: None,
        }
    }
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Part {
    pub id: String,
    pub name: String,
    pub short_name: String,
    pub staves: Vec<Staff>,
    /// MIDI channel (0–15). Channel 9 is conventionally used for percussion.
    #[serde(default)]
    pub midi_channel: u8,
    /// General MIDI program number (0–127). Default 0 = Acoustic Grand Piano.
    #[serde(default)]
    pub midi_program: u8,
    /// MIDI pitch-bend events preserved from interchange input, in canonical 480 PPQ ticks.
    #[serde(default)]
    pub midi_pitch_bends: Vec<MidiPitchBend>,
    /// MIDI Control Change events preserved from interchange input, in canonical 480 PPQ ticks.
    #[serde(default)]
    pub midi_control_changes: Vec<MidiControlChange>,
    /// MIDI Program Change events preserved from interchange input, in canonical 480 PPQ ticks.
    #[serde(default)]
    pub midi_program_changes: Vec<MidiProgramChange>,
    /// MIDI key/channel aftertouch events preserved from interchange input, in canonical 480 PPQ ticks.
    #[serde(default)]
    pub midi_aftertouch: Vec<MidiAftertouch>,
    /// MusicXML score-instrument definitions for note-level instrument IDs.
    #[serde(default)]
    pub percussion_instruments: Vec<PercussionInstrument>,
    /// MEI/MuseScore staff-group structure within this part.
    #[serde(default)]
    pub staff_groups: Vec<StaffGroup>,
    /// Optional named instrument semantics. Omitted in older score JSON.
    #[serde(default)]
    pub instrument: Option<InstrumentDefinition>,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct MidiPitchBend {
    pub tick: u64,
    pub channel: u8,
    /// Signed 14-bit MIDI bend value in the range -8192..=8191.
    pub value: i16,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct MidiControlChange {
    pub tick: u64,
    pub channel: u8,
    /// MIDI controller number (0–127).
    pub controller: u8,
    /// Seven-bit controller value (0–127).
    pub value: u8,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct MidiProgramChange {
    pub tick: u64,
    pub channel: u8,
    /// General MIDI program number (0–127).
    pub program: u8,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct MidiAftertouch {
    pub tick: u64,
    pub channel: u8,
    /// Key number for key pressure, or `None` for channel pressure.
    pub key: Option<u8>,
    /// Seven-bit pressure value (0–127).
    pub value: u8,
}

/// An editable percussion-kit mapping associated with a MusicXML score-instrument identity.
///
/// The MIDI key remains the playback fallback, while the remaining fields
/// describe renderer-independent notation defaults. Individual notes may still
/// override these defaults.
impl PercussionInstrument {
    /// Diatonic steps of a displayed unpitched note from the five-line staff's middle line
    /// (B4 in the treble/percussion layout), the unit of `staff_position`.
    pub fn display_position(pitch: &Pitch) -> i8 {
        let step = "CDEFGAB"
            .find(pitch.step.to_char())
            .map_or(0, |index| index as i32);
        let steps = i32::from(pitch.octave) * 7 + step;
        (steps - (4 * 7 + 6)).clamp(i32::from(i8::MIN), i32::from(i8::MAX)) as i8
    }
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct PercussionInstrument {
    /// Stable MusicXML score-instrument identity.
    pub id: String,
    #[serde(default)]
    pub name: Option<String>,
    /// General MIDI percussion key (0-based, 35 = acoustic bass drum, 38 = acoustic snare)
    /// played for this instrument. MusicXML `<midi-unpitched>` is 1-based and is converted
    /// on import and export.
    #[serde(default)]
    pub midi_unpitched: Option<u8>,
    /// Diatonic staff position relative to the middle line.
    #[serde(default)]
    pub staff_position: Option<i8>,
    /// Default glyph when a note does not supply a renderer-specific override.
    #[serde(default)]
    pub notehead: Option<NoteHead>,
    /// Preferred one-based score voice for newly entered kit notes.
    #[serde(default)]
    pub preferred_voice: Option<u8>,
    /// Named kit-specific variants such as rim-shot or open.
    #[serde(default)]
    pub techniques: Vec<String>,
}

impl Part {
    pub fn new(name: &str, short_name: &str) -> Self {
        Self {
            id: Uuid::new_v4().to_string(),
            name: name.to_string(),
            short_name: short_name.to_string(),
            staves: Vec::new(),
            midi_channel: 0,
            midi_program: 0,
            midi_pitch_bends: Vec::new(),
            midi_control_changes: Vec::new(),
            midi_program_changes: Vec::new(),
            midi_aftertouch: Vec::new(),
            percussion_instruments: Vec::new(),
            staff_groups: Vec::new(),
            instrument: None,
        }
    }

    /// General MIDI key to sound for pitch `pitch_index` of an unpitched note: the declared
    /// instrument's `midi_unpitched`, found by the note's `instrument_id` (for its first pitch)
    /// or else by the instrument whose `staff_position` matches the pitch's display position.
    /// `None` when the note is pitched or nothing matches; playback then uses the display
    /// pitch, as before.
    pub fn percussion_key(&self, note: &Note, pitch_index: usize) -> Option<u8> {
        if !note.is_unpitched {
            return None;
        }
        let pitch = note.pitches.get(pitch_index)?;
        let by_id = note
            .instrument_id
            .as_deref()
            .filter(|_| pitch_index == 0)
            .and_then(|id| {
                self.percussion_instruments
                    .iter()
                    .find(|instrument| instrument.id == id)
            })
            .and_then(|instrument| instrument.midi_unpitched);
        by_id.or_else(|| {
            let position = PercussionInstrument::display_position(pitch);
            self.percussion_instruments
                .iter()
                .filter(|instrument| instrument.staff_position == Some(position))
                .find_map(|instrument| instrument.midi_unpitched)
        })
    }

    /// Resolve the declared percussion instrument for an unpitched note.
    ///
    /// An explicit MusicXML `instrument@id` always takes precedence.  When no
    /// identifier is attached, the retained display-key MIDI value is matched
    /// against the part's declared `midi_unpitched` entries.  This deliberately
    /// does not invent a sound identity for an unpitched note with no matching
    /// declaration.
    pub fn percussion_instrument_for_note(&self, note: &Note) -> Option<&PercussionInstrument> {
        if !note.is_unpitched {
            return None;
        }
        if let Some(instrument_id) = note.instrument_id.as_deref() {
            return self
                .percussion_instruments
                .iter()
                .find(|instrument| instrument.id == instrument_id);
        }
        let midi_key = u8::try_from(note.pitches.first()?.to_midi()).ok()?;
        self.percussion_instruments
            .iter()
            .find(|instrument| instrument.midi_unpitched == Some(midi_key))
    }
}

/// The semantic notation mode of a staff, independent of renderer-specific styling.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
#[serde(rename_all = "snake_case")]
pub enum StaffKind {
    #[default]
    Standard,
    Tablature,
    Percussion,
}

/// A score-level notehead convention selected for an entire staff.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
#[serde(rename_all = "snake_case")]
pub enum StaffNoteheadScheme {
    #[default]
    Standard,
    PitchNames,
    ShapeNotes,
}

/// How a tablature staff exposes rhythmic duration in addition to fret numbers.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
#[serde(rename_all = "snake_case")]
pub enum TablatureRhythmDisplay {
    /// Fret numbers only; duration remains available in the score model.
    #[default]
    FretOnly,
    /// Add stems and flags to the tablature staff's fret numbers.
    Stems,
}

/// Renderer-independent staff appearance and semantic settings.
///
/// Values are expressed in staff-space units, never pixels. Existing tablature
/// tuning data remains in [`Staff::tablature`]; `kind` records how a renderer
/// should interpret the staff.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct StaffPresentation {
    #[serde(default)]
    pub kind: StaffKind,
    #[serde(default = "default_staff_line_count")]
    pub lines: u8,
    #[serde(default = "default_staff_line_distance")]
    pub line_distance: f32,
    #[serde(default)]
    pub small: bool,
    #[serde(default)]
    pub cutaway: bool,
    #[serde(default = "default_staff_visible")]
    pub visible: bool,
    #[serde(default)]
    pub notehead_scheme: StaffNoteheadScheme,
    /// Tablature-only duration presentation. Ignored on non-tablature staves.
    #[serde(default)]
    pub tablature_rhythm_display: TablatureRhythmDisplay,
    /// Tablature fret-label convention. Ignored on non-tablature staves.
    #[serde(default)]
    pub tablature_fret_mark_style: TablatureFretMarkStyle,
}

const fn default_staff_line_count() -> u8 {
    5
}

const fn default_staff_line_distance() -> f32 {
    1.0
}

const fn default_staff_visible() -> bool {
    true
}

impl Default for StaffPresentation {
    fn default() -> Self {
        Self {
            kind: StaffKind::Standard,
            lines: default_staff_line_count(),
            line_distance: default_staff_line_distance(),
            small: false,
            cutaway: false,
            visible: true,
            notehead_scheme: StaffNoteheadScheme::Standard,
            tablature_rhythm_display: TablatureRhythmDisplay::FretOnly,
            tablature_fret_mark_style: TablatureFretMarkStyle::Arabic,
        }
    }
}

/// Glyph convention used to label tablature frets.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
#[serde(rename_all = "snake_case")]
pub enum TablatureFretMarkStyle {
    #[default]
    Arabic,
    RomanUpper,
    RomanLower,
}

impl StaffPresentation {
    fn for_clef(clef: &Clef) -> Self {
        let mut presentation = Self::default();
        if matches!(clef, Clef::Percussion) {
            presentation.kind = StaffKind::Percussion;
        }
        presentation
    }
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Staff {
    pub clef: Clef,
    pub measures: Vec<Measure>,
    /// Semitones to add to written pitch for concert pitch / MIDI output.
    /// -2 = Bb instrument (clarinet, trumpet), -9 = Eb instrument (alto sax), etc.
    #[serde(default)]
    pub transpose_semitones: i8,
    #[serde(default)]
    pub tablature: Option<TablatureConfig>,
    #[serde(default)]
    pub presentation: StaffPresentation,
}

impl Staff {
    /// The meter in force at `measure_index`: that bar's time signature or the last one before
    /// it, else `default` (the score's). A bar without its own signature continues the meter
    /// of the change before it, not the score's opening one.
    pub fn meter_at<'a>(
        &'a self,
        measure_index: usize,
        default: &'a TimeSignature,
    ) -> &'a TimeSignature {
        self.measures
            .iter()
            .take(measure_index.saturating_add(1))
            .rev()
            .find_map(|measure| measure.time_sig.as_ref())
            .unwrap_or(default)
    }

    /// A bar's length in beats: its `actual_length`, else the meter in force there.
    pub fn measure_beats(&self, measure_index: usize, default: &TimeSignature) -> f64 {
        self.measures.get(measure_index).map_or_else(
            || self.meter_at(measure_index, default).total_beats(),
            |measure| measure.duration_beats(self.meter_at(measure_index, default)),
        )
    }

    pub fn new(clef: Clef) -> Self {
        Self {
            presentation: StaffPresentation::for_clef(&clef),
            clef,
            measures: Vec::new(),
            transpose_semitones: 0,
            tablature: None,
        }
    }

    /// Resolve the tablature tuning and capo active at a physical measure.
    ///
    /// A measure-local change starts at its own boundary and continues until
    /// replaced or cleared. Line-count changes are rejected by validation so
    /// the staff geometry remains stable within a system.
    pub fn tablature_at(&self, measure_index: usize) -> Option<TablatureConfig> {
        let mut active = self.tablature.clone();
        for measure in self.measures.iter().take(measure_index.saturating_add(1)) {
            if let Some(change) = &measure.tablature_change {
                active = Some(change.clone());
            }
        }
        active
    }
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct VoltaBracket {
    /// Ending number (1, 2, …); the first when the ending serves several passes.
    pub number: u8,
    /// "begin" | "mid" | "end" | "begin_end"
    pub kind: String,
    /// Every pass the ending is played on when it serves several (`1, 2` or `1-3`); empty
    /// (the usual case) means `number` alone.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub numbers: Vec<u8>,
}

impl VoltaBracket {
    /// The passes this ending is played on, in order.
    pub fn passes(&self) -> Vec<u8> {
        if self.numbers.is_empty() {
            vec![self.number]
        } else {
            self.numbers.clone()
        }
    }

    /// Whether the ending is played on repeat pass `pass` (1 = first time through).
    pub fn plays_on(&self, pass: u8) -> bool {
        if self.numbers.is_empty() {
            self.number == pass
        } else {
            self.numbers.contains(&pass)
        }
    }

    /// The ending's label as scores print it: `1`, `1, 2`, `1-3` (a run of three or more).
    pub fn label(&self) -> String {
        let passes = self.passes();
        match passes.as_slice() {
            [first, .., last]
                if passes.len() >= 3 && passes.windows(2).all(|pair| pair[1] == pair[0] + 1) =>
            {
                format!("{first}-{last}")
            }
            _ => passes
                .iter()
                .map(u8::to_string)
                .collect::<Vec<_>>()
                .join(", "),
        }
    }

    /// Pass numbers from a label such as `1`, `1, 2`, `1.2.` or `1-3`.
    pub fn parse_passes(label: &str) -> Vec<u8> {
        let mut passes = Vec::new();
        for part in label
            .split([',', ' ', '.', '+', '/'])
            .filter(|part| !part.is_empty())
        {
            if let Some((from, to)) = part.split_once(['-', '–'])
                && let (Ok(from), Ok(to)) = (from.trim().parse::<u8>(), to.trim().parse::<u8>())
                && from <= to
                && to - from < 32
            {
                passes.extend(from..=to);
            } else if let Ok(pass) = part.trim().parse::<u8>() {
                passes.push(pass);
            }
        }
        passes.sort_unstable();
        passes.dedup();
        passes
    }
}

/// One of the three mechanically available positions of a concert-harp pedal.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
#[serde(rename_all = "kebab-case")]
pub enum HarpPedalPosition {
    Flat,
    #[default]
    Natural,
    Sharp,
}

/// A MusicXML-compatible harp-pedal diagram attached to one measure.
///
/// Positions are always ordered D, C, B, E, F, G, A, which is the conventional two-row
/// pedal-diagram order. The optional placement is retained without inventing pixel geometry.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct HarpPedalDiagram {
    #[serde(default)]
    pub positions: [HarpPedalPosition; 7],
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub placement: Option<String>,
}

impl Default for HarpPedalDiagram {
    fn default() -> Self {
        Self {
            positions: [HarpPedalPosition::Natural; 7],
            placement: None,
        }
    }
}

/// Authored length of a measure that differs from its time signature: a pickup (anacrusis), an
/// incomplete final bar, or any irregular bar, as MuseScore's measure `len="1/4"`. The value is a
/// fraction of a whole note, so `1/4` lasts one quarter-note beat.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub struct MeasureLength {
    pub numerator: u32,
    pub denominator: u32,
}

impl MeasureLength {
    /// Largest supported measure length, in quarter-note beats.
    pub const MAX_BEATS: f64 = 256.0;

    /// Length in quarter-note beats, or `None` for a zero, non-finite, or oversized fraction.
    pub fn beats(&self) -> Option<f64> {
        if self.numerator == 0 || self.denominator == 0 {
            return None;
        }
        let beats = 4.0 * f64::from(self.numerator) / f64::from(self.denominator);
        (beats.is_finite() && beats <= Self::MAX_BEATS).then_some(beats)
    }

    /// Fraction for a length in quarter-note beats, exact for binary, triplet, quintuplet
    /// and septuplet subdivisions; `None` for a zero, negative, or oversized length.
    pub fn from_beats(beats: f64) -> Option<Self> {
        const DIVISIONS: u32 = 3 * 5 * 7 * 64;
        if !beats.is_finite() || beats <= 0.0 || beats > Self::MAX_BEATS {
            return None;
        }
        let ticks = (beats * f64::from(DIVISIONS)).round();
        (ticks >= 1.0).then(|| Self::from_ticks(ticks as u32, DIVISIONS))?
    }

    /// Exact fraction for `ticks` at `divisions` ticks per quarter note, in lowest terms.
    pub fn from_ticks(ticks: u32, divisions: u32) -> Option<Self> {
        let numerator = u64::from(ticks);
        let denominator = u64::from(divisions).checked_mul(4)?;
        if numerator == 0 || denominator == 0 {
            return None;
        }
        let gcd = {
            let (mut a, mut b) = (numerator, denominator);
            while b != 0 {
                (a, b) = (b, a % b);
            }
            a
        };
        let length = Self {
            numerator: u32::try_from(numerator / gcd).ok()?,
            denominator: u32::try_from(denominator / gcd).ok()?,
        };
        length.beats().map(|_| length)
    }
}

/// A clef change partway through a staff's measure. `offset` is the time from the start of
/// the bar at which the new clef takes effect, as a fraction of a whole note (`1/4` = one
/// quarter-note beat). A change at the barline itself is [`Measure::clef`] instead.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct MidMeasureClef {
    pub offset: MeasureLength,
    pub clef: Clef,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Measure {
    pub number: u32,
    pub time_sig: Option<TimeSignature>,
    pub key_sig: Option<KeySignature>,
    pub clef: Option<Clef>,
    /// Clef changes inside the bar, in increasing `offset` order, each strictly after the
    /// bar's start and before its end. Notes from an offset on are read in that clef.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub mid_clefs: Vec<MidMeasureClef>,
    pub tempo: Option<u16>,
    /// Optional target BPM at this measure's end. The playback contract linearly interpolates
    /// BPM across the measure; `None` keeps a constant tempo until the next change.
    #[serde(default)]
    pub tempo_ramp_to: Option<u16>,
    /// Instrument semantics beginning at this staff-local measure boundary.
    #[serde(default)]
    pub instrument_change: Option<InstrumentDefinition>,
    /// Tablature tuning/capo beginning at this staff-local measure boundary.
    #[serde(default)]
    pub tablature_change: Option<TablatureConfig>,
    pub barline_left: Barline,
    pub barline_right: Barline,
    #[serde(default)]
    pub volta: Option<VoltaBracket>,
    #[serde(default)]
    pub tempo_text: Option<String>,
    #[serde(default)]
    pub rehearsal: Option<String>,
    /// Navigation mark: "Segno" | "Coda" | "Fine" | "DaCapo" | "DaCapoAlFine" |
    /// "DaCapoAlCoda" | "DalSegno" | "DalSegnoAlFine" | "DalSegnoAlCoda" | "ToCoda"
    #[serde(default)]
    pub navigation: Option<String>,
    /// Expression / performance text ("dolce", "espressivo", "con fuoco", etc.).
    #[serde(default)]
    pub expression_text: Option<String>,
    #[serde(default)]
    pub texts: Vec<StyledText>,
    /// Structured MusicXML figured-bass figures in source order.
    #[serde(default)]
    pub figured_bass: Vec<FiguredBassFigure>,
    /// Concert-harp pedal diagrams declared by MusicXML `<harp-pedals>` directions.
    #[serde(default)]
    pub harp_pedal_diagrams: Vec<HarpPedalDiagram>,
    /// When ≥ 2, this measure is displayed as a multi-measure rest spanning N measures.
    #[serde(default)]
    pub multi_rest_count: Option<u8>,
    /// Force a new system (row) after this measure.
    #[serde(default)]
    pub system_break: bool,
    /// Force a new page after this measure.
    #[serde(default)]
    pub page_break: bool,
    /// Semantic section boundary beginning at this measure. Unlike system and page breaks,
    /// this is an editor/navigation marker and has no layout implication.
    #[serde(default)]
    pub section_break: bool,
    /// Up to 4 voices; voice 0 is the primary voice.
    pub voices: [Vec<Note>; 4],
    /// Original positive MusicXML voice numbers associated with the four editable slots.
    ///
    /// `None` retains the legacy convention that slot `n` serializes as voice `n + 1`.
    /// This lets import preserve sparse source identifiers such as voices 1 and 5 without
    /// changing the established fixed-slot editing API.
    #[serde(default)]
    pub source_voice_numbers: [Option<u32>; 4],
    /// Authored length when it differs from the time signature (pickup or irregular bar).
    /// `None` means the measure lasts exactly one bar of its time signature.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub actual_length: Option<MeasureLength>,
    /// Display this measure as a repeat of the previous `n` measures (MuseScore measure repeat,
    /// MusicXML `<measure-repeat>`). Its voices hold a copy of the repeated content, so playback,
    /// validation, and editing see real notes; renderers draw the repeat sign instead.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub measure_repeat: Option<u8>,
}

impl Measure {
    /// The clef in effect `beats` quarter-note beats into this bar, given the clef in effect
    /// at its start (after [`Measure::clef`]): the latest mid-bar change at or before `beats`.
    pub fn clef_at(&self, start_clef: &Clef, beats: f64) -> Clef {
        self.mid_clefs
            .iter()
            .take_while(|change| {
                change
                    .offset
                    .beats()
                    .is_some_and(|offset| offset <= beats + 1e-9)
            })
            .last()
            .map_or_else(|| start_clef.clone(), |change| change.clef.clone())
    }

    pub fn empty(numerator: u8, denominator: u8) -> Self {
        let total_beats = TimeSignature {
            numerator,
            denominator,
        }
        .total_beats();
        let mut voice0: Vec<Note> = Vec::new();
        let mut remaining = total_beats;
        while remaining > 1e-9 {
            let dur = Duration::whole_filling_beats(remaining);
            remaining -= dur.beats(0);
            voice0.push(Note::rest(dur));
        }
        Self {
            number: 0,
            time_sig: None,
            key_sig: None,
            clef: None,
            mid_clefs: Vec::new(),
            tempo: None,
            tempo_ramp_to: None,
            instrument_change: None,
            tablature_change: None,
            barline_left: Barline::Normal,
            barline_right: Barline::Normal,
            volta: None,
            tempo_text: None,
            rehearsal: None,
            navigation: None,
            expression_text: None,
            texts: Vec::new(),
            figured_bass: Vec::new(),
            harp_pedal_diagrams: Vec::new(),
            multi_rest_count: None,
            system_break: false,
            page_break: false,
            section_break: false,
            voices: [voice0, vec![], vec![], vec![]],
            source_voice_numbers: [None; 4],
            actual_length: None,
            measure_repeat: None,
        }
    }

    /// Replace this measure's voices with a playable copy of `source`, as a measure repeat
    /// stores its repeated content; see [`Note::repeated_copy`].
    pub fn repeat_content_from(&mut self, source: &Measure) {
        for (target, voice) in self.voices.iter_mut().zip(&source.voices) {
            *target = voice.iter().map(Note::repeated_copy).collect();
        }
        self.source_voice_numbers = source.source_voice_numbers;
    }

    /// Whether this measure's voices sound like `other`'s: the same rests, pitches, durations,
    /// dots, and tuplets in every voice.
    pub fn same_sounding_content(&self, other: &Measure) -> bool {
        self.voices.iter().zip(&other.voices).all(|(left, right)| {
            left.len() == right.len()
                && left.iter().zip(right).all(|(a, b)| {
                    a.is_rest == b.is_rest
                        && a.pitches == b.pitches
                        && a.duration == b.duration
                        && a.dot_count == b.dot_count
                        && a.tuplet == b.tuplet
                        && a.is_grace == b.is_grace
                })
        })
    }

    /// Beats this measure lasts: its [`actual_length`](Self::actual_length) when present and
    /// valid, otherwise its own time signature, otherwise `time_signature` (the one in effect).
    pub fn duration_beats(&self, time_signature: &TimeSignature) -> f64 {
        self.actual_length
            .and_then(|length| length.beats())
            .unwrap_or_else(|| {
                self.time_sig
                    .as_ref()
                    .unwrap_or(time_signature)
                    .total_beats()
            })
    }

    pub fn renumber(&mut self, n: u32) {
        self.number = n;
    }
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Note {
    pub id: String,
    pub is_rest: bool,
    /// MusicXML unpitched note; `pitches` then stores display placement only.
    #[serde(default)]
    pub is_unpitched: bool,
    /// Optional source instrument identifier (for example MusicXML note-level `instrument@id`).
    #[serde(default)]
    pub instrument_id: Option<String>,
    /// Horizontal nudge in tenths from the note's computed (rhythmic) position, set by hosts.
    /// MusicXML import does not fill it from `default-x`, which is an absolute position in the
    /// source engraver's layout; MusicXML export writes it as part of `relative-x`.
    #[serde(default)]
    pub offset_x: Option<f64>,
    /// Vertical nudge in tenths from the note's staff position; see `offset_x`.
    #[serde(default)]
    pub offset_y: Option<f64>,
    /// MusicXML note-level horizontal adjustment in tenths.
    #[serde(default)]
    pub relative_x: Option<f64>,
    /// MusicXML note-level vertical adjustment in tenths.
    #[serde(default)]
    pub relative_y: Option<f64>,
    /// Single note: one pitch. Chord: multiple pitches (same duration).
    pub pitches: Vec<Pitch>,
    #[serde(default)]
    pub tab_position: Option<super::notation::TabPosition>,
    /// One tablature position per pitch; the first entry mirrors `tab_position`.
    /// This is populated for chords so each pitch can occupy a distinct string.
    #[serde(default)]
    pub tab_positions: Vec<super::notation::TabPosition>,
    pub duration: Duration,
    pub dot_count: u8,
    pub tie_start: bool,
    pub tie_end: bool,
    /// Per-pitch tie starts, parallel to `pitches`, for a chord whose notes are not all tied.
    /// Empty (the usual case) means `tie_start` applies to every pitch. A vector whose length
    /// differs from `pitches` is ignored in favour of `tie_start`; see [`Note::pitch_tie_start`].
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub pitch_tie_starts: Vec<bool>,
    /// Per-pitch tie ends, parallel to `pitches`; empty means `tie_end` applies to every pitch.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub pitch_tie_ends: Vec<bool>,
    /// Per-pitch accidental display, parallel to `pitches`. Empty (the usual case) leaves every
    /// accidental to the notation rules; pitches past the end are `Auto`, and a vector longer
    /// than `pitches` is ignored. See [`Note::accidental_display`].
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub pitch_accidentals: Vec<AccidentalDisplay>,
    /// Per-pitch parenthesized noteheads (ghost notes), parallel to `pitches`: MusicXML
    /// `<notehead parentheses="yes">`, MEI `@enclose="paren"`, MuseScore `<ghost>`, Guitar Pro
    /// ghost notes. Empty (the usual case) means none; pitches past the end are not
    /// parenthesized, and a vector longer than `pitches` is ignored.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub pitch_parentheses: Vec<bool>,
    /// Left-hand fingering per chord member, parallel to `pitches` (MusicXML `<fingering>` on
    /// each `<chord/>` note, MuseScore `<Fingering>` in each `<Note>`, Guitar Pro fingering on
    /// each string). Empty unless a chord's fingerings belong to particular notes;
    /// `fingering`/`fingerings` still hold them all for display.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub pitch_fingerings: Vec<Option<u8>>,
    pub beam: BeamState,
    pub articulations: Vec<Articulation>,
    pub dynamic: Option<Dynamic>,
    pub stem_up: Option<bool>,
    #[serde(default)]
    pub hairpin_start: Option<HairpinKind>,
    #[serde(default)]
    pub hairpin_end: bool,
    #[serde(default)]
    pub tuplet: Option<TupletInfo>,
    #[serde(default)]
    pub chord_symbol: Option<ChordSymbol>,
    #[serde(default)]
    pub is_grace: bool,
    /// Acciaccatura: true (slash through stem). Appoggiatura: false.
    #[serde(default)]
    pub grace_slash: bool,
    #[serde(default)]
    pub ottava_start: Option<OttavaKind>,
    #[serde(default)]
    pub ottava_end: bool,
    #[serde(default)]
    pub lyric: Option<Lyric>,
    /// Lyrics for verse 2 and later, in ascending verse order; verse 1 is [`lyric`](Self::lyric).
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub additional_lyrics: Vec<VerseLyric>,
    #[serde(default)]
    pub pedal_start: bool,
    #[serde(default)]
    pub pedal_end: bool,
    #[serde(default)]
    pub slur_start: bool,
    #[serde(default)]
    pub slur_end: bool,
    /// Arpeggiate direction: `Some(true)` = up, `Some(false)` = down, `None` = none.
    #[serde(default)]
    pub arpeggiate: Option<bool>,
    /// Technique/style instruction attached to this note ("pizz.", "arco", "con sord.", etc.).
    #[serde(default)]
    pub technique_text: Option<String>,
    #[serde(default)]
    pub glissando_start: bool,
    #[serde(default)]
    pub glissando_end: bool,
    #[serde(default)]
    pub cross_staff: Option<CrossStaff>,
    /// Left-hand fingering number (0 = open / thumb, 1–5 = fingers).
    #[serde(default)]
    pub fingering: Option<u8>,
    /// Alternate left-hand fingering candidates, in source order. The first
    /// entry mirrors `fingering` when present.
    #[serde(default)]
    pub fingerings: Vec<u8>,
    /// String number for plucked/bowed string instruments (1 = highest string).
    #[serde(default)]
    pub string_number: Option<u8>,
    #[serde(default)]
    pub note_head: NoteHead,
    /// Cue note (small-sized, does not count toward beat total).
    #[serde(default)]
    pub is_cue: bool,
    /// Not drawn (MusicXML `print-object="no"`, MEI `@visible="false"`, MuseScore
    /// `<visible>0</visible>`): the note or rest still takes its time and sounds, as a hidden
    /// rest in a second voice or a written-out trill does.
    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
    pub hidden: bool,
    /// Start of a multi-note trill line span.
    #[serde(default)]
    pub trill_line_start: bool,
    /// End of a multi-note trill line span.
    #[serde(default)]
    pub trill_line_end: bool,
    /// Guitar-specific playing technique (bend, slide, hammer-on, pull-off).
    #[serde(default)]
    pub guitar_technique: Option<GuitarTechnique>,
    /// MusicXML bend amount in cents when supplied by the source.
    #[serde(default)]
    pub guitar_bend_alter_cents: Option<i16>,
    /// Ordered bend curve points. Position is relative note time in per-mille (0..=1000).
    #[serde(default)]
    pub guitar_bend_curve: Vec<GuitarBendPoint>,
}

/// One point of an authored guitar bend curve.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub struct GuitarBendPoint {
    pub position_per_mille: u16,
    pub alter_cents: i16,
}

impl Note {
    /// Select one authored fingering candidate without changing the score.
    pub fn select_fingering(
        &self,
        policy: super::notation::FingeringSelectionPolicy,
    ) -> Option<u8> {
        let candidates = if self.fingerings.is_empty() {
            self.fingering.into_iter().collect::<Vec<_>>()
        } else {
            self.fingerings.clone()
        };
        match policy {
            super::notation::FingeringSelectionPolicy::SourceOrder => candidates.first().copied(),
            super::notation::FingeringSelectionPolicy::LowestNumber => {
                candidates.iter().copied().min()
            }
            super::notation::FingeringSelectionPolicy::HighestNumber => {
                candidates.iter().copied().max()
            }
        }
    }

    pub fn new(pitch: Pitch, duration: Duration) -> Self {
        Self {
            id: Uuid::new_v4().to_string(),
            is_rest: false,
            is_unpitched: false,
            instrument_id: None,
            offset_x: None,
            offset_y: None,
            relative_x: None,
            relative_y: None,
            pitches: vec![pitch],
            tab_position: None,
            tab_positions: Vec::new(),
            duration,
            dot_count: 0,
            tie_start: false,
            tie_end: false,
            pitch_tie_starts: Vec::new(),
            pitch_tie_ends: Vec::new(),
            pitch_accidentals: Vec::new(),
            pitch_parentheses: Vec::new(),
            pitch_fingerings: Vec::new(),
            beam: BeamState::None,
            articulations: Vec::new(),
            dynamic: None,
            stem_up: None,
            hairpin_start: None,
            hairpin_end: false,
            tuplet: None,
            chord_symbol: None,
            is_grace: false,
            grace_slash: false,
            ottava_start: None,
            ottava_end: false,
            lyric: None,
            additional_lyrics: Vec::new(),
            pedal_start: false,
            pedal_end: false,
            slur_start: false,
            slur_end: false,
            arpeggiate: None,
            technique_text: None,
            glissando_start: false,
            glissando_end: false,
            cross_staff: None,
            fingering: None,
            fingerings: Vec::new(),
            string_number: None,
            note_head: NoteHead::Normal,
            is_cue: false,
            hidden: false,
            trill_line_start: false,
            trill_line_end: false,
            guitar_technique: None,
            guitar_bend_alter_cents: None,
            guitar_bend_curve: Vec::new(),
        }
    }

    pub fn rest(duration: Duration) -> Self {
        Self {
            id: Uuid::new_v4().to_string(),
            is_rest: true,
            is_unpitched: false,
            instrument_id: None,
            offset_x: None,
            offset_y: None,
            relative_x: None,
            relative_y: None,
            pitches: Vec::new(),
            tab_position: None,
            tab_positions: Vec::new(),
            duration,
            dot_count: 0,
            tie_start: false,
            tie_end: false,
            pitch_tie_starts: Vec::new(),
            pitch_tie_ends: Vec::new(),
            pitch_accidentals: Vec::new(),
            pitch_parentheses: Vec::new(),
            pitch_fingerings: Vec::new(),
            beam: BeamState::None,
            articulations: Vec::new(),
            dynamic: None,
            stem_up: None,
            hairpin_start: None,
            hairpin_end: false,
            tuplet: None,
            chord_symbol: None,
            is_grace: false,
            grace_slash: false,
            ottava_start: None,
            ottava_end: false,
            lyric: None,
            additional_lyrics: Vec::new(),
            pedal_start: false,
            pedal_end: false,
            slur_start: false,
            slur_end: false,
            arpeggiate: None,
            technique_text: None,
            glissando_start: false,
            glissando_end: false,
            cross_staff: None,
            fingering: None,
            fingerings: Vec::new(),
            string_number: None,
            note_head: NoteHead::Normal,
            is_cue: false,
            hidden: false,
            trill_line_start: false,
            trill_line_end: false,
            guitar_technique: None,
            guitar_bend_alter_cents: None,
            guitar_bend_curve: Vec::new(),
        }
    }

    /// Copy for a repeated measure: a fresh id and the same sounding content, without ties,
    /// slurs, lines, lyrics, chord symbol, or dynamic, which belong to the written original.
    pub fn repeated_copy(&self) -> Note {
        let mut copy = self.clone();
        copy.id = Uuid::new_v4().to_string();
        copy.tie_start = false;
        copy.tie_end = false;
        copy.slur_start = false;
        copy.slur_end = false;
        copy.hairpin_start = None;
        copy.hairpin_end = false;
        copy.pedal_start = false;
        copy.pedal_end = false;
        copy.ottava_start = None;
        copy.ottava_end = false;
        copy.glissando_start = false;
        copy.glissando_end = false;
        copy.trill_line_start = false;
        copy.trill_line_end = false;
        copy.lyric = None;
        copy.additional_lyrics.clear();
        copy.chord_symbol = None;
        copy.dynamic = None;
        copy
    }

    /// Whether the pitch at `index` starts a tie: its own flag when per-pitch ties are recorded,
    /// otherwise the chord-level `tie_start`.
    pub fn pitch_tie_start(&self, index: usize) -> bool {
        per_pitch_flag(
            &self.pitch_tie_starts,
            self.pitches.len(),
            index,
            self.tie_start,
        )
    }

    /// Whether the pitch at `index` ends a tie; see [`Note::pitch_tie_start`].
    pub fn pitch_tie_end(&self, index: usize) -> bool {
        per_pitch_flag(
            &self.pitch_tie_ends,
            self.pitches.len(),
            index,
            self.tie_end,
        )
    }

    /// Record which pitches of this note start (`starts`) and end (`ends`) a tie. The chord-level
    /// flags become "any pitch", and per-pitch vectors are kept only when the pitches differ, so a
    /// uniformly tied chord stays in the plain form. Slices whose length is not the pitch count
    /// are ignored.
    pub fn set_pitch_ties(&mut self, starts: &[bool], ends: &[bool]) {
        let count = self.pitches.len();
        if starts.len() == count {
            self.tie_start = starts.iter().any(|tied| *tied);
            self.pitch_tie_starts = if starts.iter().all(|tied| *tied == self.tie_start) {
                Vec::new()
            } else {
                starts.to_vec()
            };
        }
        if ends.len() == count {
            self.tie_end = ends.iter().any(|tied| *tied);
            self.pitch_tie_ends = if ends.iter().all(|tied| *tied == self.tie_end) {
                Vec::new()
            } else {
                ends.to_vec()
            };
        }
    }

    /// How the accidental of the pitch at `index` is shown (`Auto` when not recorded).
    pub fn accidental_display(&self, index: usize) -> AccidentalDisplay {
        if self.pitch_accidentals.len() > self.pitches.len() {
            return AccidentalDisplay::Auto;
        }
        self.pitch_accidentals
            .get(index)
            .copied()
            .unwrap_or_default()
    }

    /// Set how the accidental of the pitch at `index` is shown. The vector is dropped again
    /// when every pitch is back to `Auto`.
    pub fn set_accidental_display(&mut self, index: usize, display: AccidentalDisplay) {
        if index >= self.pitches.len() {
            return;
        }
        if self.pitch_accidentals.len() > self.pitches.len() {
            self.pitch_accidentals.clear();
        }
        self.pitch_accidentals
            .resize(self.pitches.len(), AccidentalDisplay::Auto);
        self.pitch_accidentals[index] = display;
        if self
            .pitch_accidentals
            .iter()
            .all(|display| *display == AccidentalDisplay::Auto)
        {
            self.pitch_accidentals.clear();
        }
    }

    /// The fingering of the chord member at `index`, when fingerings are recorded per pitch.
    pub fn pitch_fingering(&self, index: usize) -> Option<u8> {
        if self.pitch_fingerings.len() > self.pitches.len() {
            return None;
        }
        self.pitch_fingerings.get(index).copied().flatten()
    }

    /// Record the fingering of the chord member at `index` (and add it to the displayed
    /// fingerings).
    pub fn set_pitch_fingering(&mut self, index: usize, fingering: u8) {
        if index >= self.pitches.len() {
            return;
        }
        if self.pitch_fingerings.len() > self.pitches.len() {
            self.pitch_fingerings.clear();
        }
        if self.pitch_fingerings.len() <= index {
            self.pitch_fingerings.resize(index + 1, None);
        }
        self.pitch_fingerings[index] = Some(fingering);
        if self.fingering.is_none() {
            self.fingering = Some(fingering);
        }
        self.fingerings.push(fingering);
    }

    /// Whether the notehead of the pitch at `index` is in parentheses (a ghost note).
    pub fn is_parenthesized(&self, index: usize) -> bool {
        self.pitch_parentheses.len() <= self.pitches.len()
            && self.pitch_parentheses.get(index).copied().unwrap_or(false)
    }

    /// Put the notehead of the pitch at `index` in parentheses or take it out. The vector is
    /// dropped again when no pitch is parenthesized.
    pub fn set_parenthesized(&mut self, index: usize, parenthesized: bool) {
        if index >= self.pitches.len() {
            return;
        }
        if self.pitch_parentheses.len() > self.pitches.len() {
            self.pitch_parentheses.clear();
        }
        self.pitch_parentheses.resize(self.pitches.len(), false);
        self.pitch_parentheses[index] = parenthesized;
        if !self.pitch_parentheses.contains(&true) {
            self.pitch_parentheses.clear();
        }
    }

    /// Per-pitch tie starts as a full vector (chord-level flag repeated when not recorded).
    pub fn pitch_tie_starts_or_uniform(&self) -> Vec<bool> {
        (0..self.pitches.len())
            .map(|index| self.pitch_tie_start(index))
            .collect()
    }

    /// Per-pitch tie ends as a full vector (chord-level flag repeated when not recorded).
    pub fn pitch_tie_ends_or_uniform(&self) -> Vec<bool> {
        (0..self.pitches.len())
            .map(|index| self.pitch_tie_end(index))
            .collect()
    }

    /// A plain whole rest, the form MusicXML `<rest measure="yes"/>` and MuseScore
    /// `durationType=measure` import to. Alone in a voice it is a measure rest; see
    /// [`voice_duration_beats`].
    pub fn is_plain_whole_rest(&self) -> bool {
        self.is_rest
            && matches!(self.duration, Duration::Whole)
            && self.dot_count == 0
            && self.tuplet.is_none()
            && !self.is_grace
            && !self.is_cue
    }

    pub fn beats(&self) -> f64 {
        if self.is_grace || self.is_cue {
            return 0.0;
        }
        let base = self.duration.beats(self.dot_count);
        if let Some(ref t) = self.tuplet {
            base * (t.normal_notes as f64) / (t.actual_notes as f64)
        } else {
            base
        }
    }
}

impl Duration {
    /// Returns the largest single duration that fills the given number of beats.
    pub fn whole_filling_beats(beats: f64) -> Duration {
        if beats >= 16.0 {
            Duration::Longa
        } else if beats >= 8.0 {
            Duration::Breve
        } else if beats >= 4.0 {
            Duration::Whole
        } else if beats >= 2.0 {
            Duration::Half
        } else if beats >= 1.0 {
            Duration::Quarter
        } else if beats >= 0.5 {
            Duration::Eighth
        } else if beats >= 0.25 {
            Duration::Sixteenth
        } else if beats >= 0.125 {
            Duration::ThirtySecond
        } else if beats >= 0.0625 {
            Duration::SixtyFourth
        } else {
            Duration::HundredTwentyEighth
        }
    }
}

// ── NoteAddr ──────────────────────────────────────────────────────────────────

/// Physical address of a note within a score.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct NoteAddr {
    pub part: usize,
    pub staff: usize,
    pub measure: usize,
    pub voice: usize,
    pub note: usize,
}

// ── diff ──────────────────────────────────────────────────────────────────────

/// A single change between two [`Score`] values as reported by [`diff`].
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum ScoreChange {
    ScoreViewsChanged {
        old: Vec<ScoreView>,
        new: Vec<ScoreView>,
    },
    ScoreTextChanged {
        old: Vec<StyledText>,
        new: Vec<StyledText>,
    },
    MeasureTextChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old: Vec<StyledText>,
        new: Vec<StyledText>,
    },
    FiguredBassChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old: Vec<FiguredBassFigure>,
        new: Vec<FiguredBassFigure>,
    },
    HarpPedalDiagramsChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old: Vec<HarpPedalDiagram>,
        new: Vec<HarpPedalDiagram>,
    },
    ChordDefinitionsChanged {
        old: Vec<ChordDefinition>,
        new: Vec<ChordDefinition>,
    },
    PartNamesChanged {
        part: usize,
        old_name: String,
        new_name: String,
        old_short_name: String,
        new_short_name: String,
    },
    PartMidiChanged {
        part: usize,
        old_channel: u8,
        new_channel: u8,
        old_program: u8,
        new_program: u8,
    },
    InstrumentDefinitionChanged {
        part: usize,
        old: Option<InstrumentDefinition>,
        new: Option<InstrumentDefinition>,
    },
    PartMidiAutomationChanged {
        part: usize,
        old_pitch_bends: Vec<MidiPitchBend>,
        new_pitch_bends: Vec<MidiPitchBend>,
        old_control_changes: Vec<MidiControlChange>,
        new_control_changes: Vec<MidiControlChange>,
        old_program_changes: Vec<MidiProgramChange>,
        new_program_changes: Vec<MidiProgramChange>,
        old_aftertouch: Vec<MidiAftertouch>,
        new_aftertouch: Vec<MidiAftertouch>,
    },
    StaffConfigurationChanged {
        part: usize,
        staff: usize,
        old_clef: Clef,
        new_clef: Clef,
        old_transpose_semitones: i8,
        new_transpose_semitones: i8,
    },
    StaffPresentationChanged {
        part: usize,
        staff: usize,
        old: StaffPresentation,
        new: StaffPresentation,
    },
    MeasurePresentationChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old_number: u32,
        new_number: u32,
        old_clef: Option<Clef>,
        new_clef: Option<Clef>,
        old_tempo_text: Option<String>,
        new_tempo_text: Option<String>,
        old_navigation: Option<String>,
        new_navigation: Option<String>,
        old_expression_text: Option<String>,
        new_expression_text: Option<String>,
        old_multi_rest_count: Option<u8>,
        new_multi_rest_count: Option<u8>,
        old_system_break: bool,
        new_system_break: bool,
        old_page_break: bool,
        new_page_break: bool,
        old_section_break: bool,
        new_section_break: bool,
    },
    TablatureConfigChanged {
        part: usize,
        staff: usize,
        old: Option<TablatureConfig>,
        new: Option<TablatureConfig>,
    },
    TablatureChangeChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old: Option<TablatureConfig>,
        new: Option<TablatureConfig>,
    },
    MidMeasureClefsChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old: Vec<MidMeasureClef>,
        new: Vec<MidMeasureClef>,
    },
    /// A semantic field changed without a dedicated positional diff variant.
    ///
    /// The stable path keeps compatibility reports honest while the complete score remains
    /// available through [`ScorePatch::ReplaceScore`].
    UnrepresentedFieldChanged {
        path: String,
    },
    MetadataChanged {
        field: String,
        old: String,
        new: String,
    },
    TempoChanged {
        old: u16,
        new: u16,
    },
    KeySignatureChanged {
        old: KeySignature,
        new: KeySignature,
    },
    PartAdded {
        part_index: usize,
    },
    PartRemoved {
        part_index: usize,
        name: String,
    },
    NoteAdded {
        part: usize,
        staff: usize,
        measure: usize,
        voice: usize,
        note_index: usize,
    },
    NoteRemoved {
        part: usize,
        staff: usize,
        measure: usize,
        voice: usize,
        note: Box<Note>,
    },
    NoteModified {
        part: usize,
        staff: usize,
        measure: usize,
        voice: usize,
        note_index: usize,
        old: Box<Note>,
        new: Box<Note>,
    },
    TimeSigChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old: Option<TimeSignature>,
        new: Option<TimeSignature>,
    },
    MeasureTempoChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old: Option<u16>,
        new: Option<u16>,
    },
    MeasureTempoRampChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old: Option<u16>,
        new: Option<u16>,
    },
    BarlineChanged {
        part: usize,
        staff: usize,
        measure: usize,
    },
    RehearsalMarkChanged {
        part: usize,
        staff: usize,
        measure: usize,
        old: Option<String>,
        new: Option<String>,
    },
    VoltaChanged {
        part: usize,
        staff: usize,
        measure: usize,
    },
}

/// Compare two scores and return a list of differences.
///
/// Parts, staves, measures, and voices are compared by position. Notes are compared by
/// position within each voice, ignoring their `id` field. Metadata fields are compared
/// individually.
pub fn diff(a: &Score, b: &Score) -> Vec<ScoreChange> {
    let mut changes: Vec<ScoreChange> = Vec::new();

    if a.views != b.views {
        changes.push(ScoreChange::ScoreViewsChanged {
            old: a.views.clone(),
            new: b.views.clone(),
        });
    }

    if a.texts != b.texts {
        changes.push(ScoreChange::ScoreTextChanged {
            old: a.texts.clone(),
            new: b.texts.clone(),
        });
    }
    if a.chord_definitions != b.chord_definitions {
        changes.push(ScoreChange::ChordDefinitionsChanged {
            old: a.chord_definitions.clone(),
            new: b.chord_definitions.clone(),
        });
    }
    if let Some(path) = first_unrepresented_field_change(a, b) {
        changes.push(ScoreChange::UnrepresentedFieldChanged { path });
    }

    macro_rules! meta {
        ($field:ident, $name:literal) => {
            if a.metadata.$field != b.metadata.$field {
                changes.push(ScoreChange::MetadataChanged {
                    field: $name.to_string(),
                    old: a.metadata.$field.clone(),
                    new: b.metadata.$field.clone(),
                });
            }
        };
    }
    meta!(title, "title");
    meta!(composer, "composer");
    meta!(lyricist, "lyricist");
    meta!(copyright, "copyright");
    meta!(work_number, "work_number");
    meta!(movement_title, "movement_title");

    if a.settings.tempo_bpm != b.settings.tempo_bpm {
        changes.push(ScoreChange::TempoChanged {
            old: a.settings.tempo_bpm,
            new: b.settings.tempo_bpm,
        });
    }
    if a.settings.key_signature != b.settings.key_signature {
        changes.push(ScoreChange::KeySignatureChanged {
            old: a.settings.key_signature.clone(),
            new: b.settings.key_signature.clone(),
        });
    }

    let a_len = a.parts.len();
    let b_len = b.parts.len();
    for i in b_len..a_len {
        changes.push(ScoreChange::PartRemoved {
            part_index: i,
            name: a.parts[i].name.clone(),
        });
    }
    for i in a_len..b_len {
        changes.push(ScoreChange::PartAdded { part_index: i });
    }

    for pi in 0..a_len.min(b_len) {
        let ap = &a.parts[pi];
        let bp = &b.parts[pi];
        if ap.name != bp.name || ap.short_name != bp.short_name {
            changes.push(ScoreChange::PartNamesChanged {
                part: pi,
                old_name: ap.name.clone(),
                new_name: bp.name.clone(),
                old_short_name: ap.short_name.clone(),
                new_short_name: bp.short_name.clone(),
            });
        }
        if ap.midi_channel != bp.midi_channel || ap.midi_program != bp.midi_program {
            changes.push(ScoreChange::PartMidiChanged {
                part: pi,
                old_channel: ap.midi_channel,
                new_channel: bp.midi_channel,
                old_program: ap.midi_program,
                new_program: bp.midi_program,
            });
        }
        if ap.instrument != bp.instrument {
            changes.push(ScoreChange::InstrumentDefinitionChanged {
                part: pi,
                old: ap.instrument.clone(),
                new: bp.instrument.clone(),
            });
        }
        if ap.midi_pitch_bends != bp.midi_pitch_bends
            || ap.midi_control_changes != bp.midi_control_changes
            || ap.midi_program_changes != bp.midi_program_changes
            || ap.midi_aftertouch != bp.midi_aftertouch
        {
            changes.push(ScoreChange::PartMidiAutomationChanged {
                part: pi,
                old_pitch_bends: ap.midi_pitch_bends.clone(),
                new_pitch_bends: bp.midi_pitch_bends.clone(),
                old_control_changes: ap.midi_control_changes.clone(),
                new_control_changes: bp.midi_control_changes.clone(),
                old_program_changes: ap.midi_program_changes.clone(),
                new_program_changes: bp.midi_program_changes.clone(),
                old_aftertouch: ap.midi_aftertouch.clone(),
                new_aftertouch: bp.midi_aftertouch.clone(),
            });
        }
        for si in 0..ap.staves.len().min(bp.staves.len()) {
            let a_staff = &ap.staves[si];
            let b_staff = &bp.staves[si];
            if a_staff.clef != b_staff.clef
                || a_staff.transpose_semitones != b_staff.transpose_semitones
            {
                changes.push(ScoreChange::StaffConfigurationChanged {
                    part: pi,
                    staff: si,
                    old_clef: a_staff.clef.clone(),
                    new_clef: b_staff.clef.clone(),
                    old_transpose_semitones: a_staff.transpose_semitones,
                    new_transpose_semitones: b_staff.transpose_semitones,
                });
            }
            if a_staff.tablature != b_staff.tablature {
                changes.push(ScoreChange::TablatureConfigChanged {
                    part: pi,
                    staff: si,
                    old: a_staff.tablature.clone(),
                    new: b_staff.tablature.clone(),
                });
            }
            if a_staff.presentation != b_staff.presentation {
                changes.push(ScoreChange::StaffPresentationChanged {
                    part: pi,
                    staff: si,
                    old: a_staff.presentation.clone(),
                    new: b_staff.presentation.clone(),
                });
            }
            for mi in 0..a_staff.measures.len().min(b_staff.measures.len()) {
                let am = &a_staff.measures[mi];
                let bm = &b_staff.measures[mi];
                if am.tablature_change != bm.tablature_change {
                    changes.push(ScoreChange::TablatureChangeChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old: am.tablature_change.clone(),
                        new: bm.tablature_change.clone(),
                    });
                }
                if am.mid_clefs != bm.mid_clefs {
                    changes.push(ScoreChange::MidMeasureClefsChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old: am.mid_clefs.clone(),
                        new: bm.mid_clefs.clone(),
                    });
                }
                if am.number != bm.number
                    || am.clef != bm.clef
                    || am.tempo_text != bm.tempo_text
                    || am.navigation != bm.navigation
                    || am.expression_text != bm.expression_text
                    || am.multi_rest_count != bm.multi_rest_count
                    || am.system_break != bm.system_break
                    || am.page_break != bm.page_break
                    || am.section_break != bm.section_break
                {
                    changes.push(ScoreChange::MeasurePresentationChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old_number: am.number,
                        new_number: bm.number,
                        old_clef: am.clef.clone(),
                        new_clef: bm.clef.clone(),
                        old_tempo_text: am.tempo_text.clone(),
                        new_tempo_text: bm.tempo_text.clone(),
                        old_navigation: am.navigation.clone(),
                        new_navigation: bm.navigation.clone(),
                        old_expression_text: am.expression_text.clone(),
                        new_expression_text: bm.expression_text.clone(),
                        old_multi_rest_count: am.multi_rest_count,
                        new_multi_rest_count: bm.multi_rest_count,
                        old_system_break: am.system_break,
                        new_system_break: bm.system_break,
                        old_page_break: am.page_break,
                        new_page_break: bm.page_break,
                        old_section_break: am.section_break,
                        new_section_break: bm.section_break,
                    });
                }
                for vi in 0..4usize {
                    let av = &am.voices[vi];
                    let bv = &bm.voices[vi];
                    for (ni, (a_note, b_note)) in av.iter().zip(bv.iter()).enumerate() {
                        if !note_content_eq(a_note, b_note) {
                            changes.push(ScoreChange::NoteModified {
                                part: pi,
                                staff: si,
                                measure: mi,
                                voice: vi,
                                note_index: ni,
                                old: Box::new(a_note.clone()),
                                new: Box::new(b_note.clone()),
                            });
                        }
                    }
                    for note in av.iter().skip(bv.len()) {
                        changes.push(ScoreChange::NoteRemoved {
                            part: pi,
                            staff: si,
                            measure: mi,
                            voice: vi,
                            note: Box::new(note.clone()),
                        });
                    }
                    for ni in av.len()..bv.len() {
                        changes.push(ScoreChange::NoteAdded {
                            part: pi,
                            staff: si,
                            measure: mi,
                            voice: vi,
                            note_index: ni,
                        });
                    }
                }
                if am.time_sig != bm.time_sig {
                    changes.push(ScoreChange::TimeSigChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old: am.time_sig.clone(),
                        new: bm.time_sig.clone(),
                    });
                }
                if am.tempo != bm.tempo {
                    changes.push(ScoreChange::MeasureTempoChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old: am.tempo,
                        new: bm.tempo,
                    });
                }
                if am.tempo_ramp_to != bm.tempo_ramp_to {
                    changes.push(ScoreChange::MeasureTempoRampChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old: am.tempo_ramp_to,
                        new: bm.tempo_ramp_to,
                    });
                }
                if am.barline_left != bm.barline_left || am.barline_right != bm.barline_right {
                    changes.push(ScoreChange::BarlineChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                    });
                }
                if am.rehearsal != bm.rehearsal {
                    changes.push(ScoreChange::RehearsalMarkChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old: am.rehearsal.clone(),
                        new: bm.rehearsal.clone(),
                    });
                }
                if am.volta != bm.volta {
                    changes.push(ScoreChange::VoltaChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                    });
                }
                if am.texts != bm.texts {
                    changes.push(ScoreChange::MeasureTextChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old: am.texts.clone(),
                        new: bm.texts.clone(),
                    });
                }
                if am.figured_bass != bm.figured_bass {
                    changes.push(ScoreChange::FiguredBassChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old: am.figured_bass.clone(),
                        new: bm.figured_bass.clone(),
                    });
                }
                if am.harp_pedal_diagrams != bm.harp_pedal_diagrams {
                    changes.push(ScoreChange::HarpPedalDiagramsChanged {
                        part: pi,
                        staff: si,
                        measure: mi,
                        old: am.harp_pedal_diagrams.clone(),
                        new: bm.harp_pedal_diagrams.clone(),
                    });
                }
            }
        }
    }

    changes
}

fn first_unrepresented_field_change(a: &Score, b: &Score) -> Option<String> {
    if a.settings.time_signature != b.settings.time_signature {
        return Some("settings.time_signature".to_string());
    }
    if a.part_groups.len() != b.part_groups.len()
        || a.part_groups.iter().zip(&b.part_groups).any(|(x, y)| {
            x.first_part != y.first_part
                || x.last_part != y.last_part
                || x.symbol != y.symbol
                || x.barlines_connect != y.barlines_connect
        })
    {
        return Some("part_groups".to_string());
    }
    a.parts
        .iter()
        .zip(&b.parts)
        .enumerate()
        .find_map(|(part_index, (ap, bp))| first_unrepresented_part_change(part_index, ap, bp))
}

fn first_unrepresented_part_change(part_index: usize, a: &Part, b: &Part) -> Option<String> {
    let prefix = format!("parts[{part_index}]");
    if a.percussion_instruments != b.percussion_instruments {
        return Some(format!("{prefix}.percussion_instruments"));
    }
    if a.staff_groups != b.staff_groups {
        return Some(format!("{prefix}.staff_groups"));
    }
    if a.staves.len() != b.staves.len() {
        return Some(format!("{prefix}.staves"));
    }
    a.staves
        .iter()
        .zip(&b.staves)
        .enumerate()
        .find_map(|(staff_index, (a, b))| {
            first_unrepresented_staff_change(&prefix, staff_index, a, b)
        })
}

fn first_unrepresented_staff_change(
    part_prefix: &str,
    staff_index: usize,
    a: &Staff,
    b: &Staff,
) -> Option<String> {
    let prefix = format!("{part_prefix}.staves[{staff_index}]");
    if a.measures.len() != b.measures.len() {
        return Some(format!("{prefix}.measures"));
    }
    a.measures
        .iter()
        .zip(&b.measures)
        .enumerate()
        .find_map(|(measure_index, (a, b))| {
            first_unrepresented_measure_change(&prefix, measure_index, a, b)
        })
}

fn first_unrepresented_measure_change(
    _staff_prefix: &str,
    _measure_index: usize,
    _a: &Measure,
    _b: &Measure,
) -> Option<String> {
    None
}

// ── ScorePatch ────────────────────────────────────────────────────────────────

/// An individually applicable patch operation produced by [`score_patch`].
///
/// Unlike [`ScoreChange`], every variant carries enough data to apply the change to a
/// [`Score`] without needing the original score. Use [`apply_patch`] to apply a list.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum ScorePatch {
    SetScoreViews {
        value: Vec<ScoreView>,
    },
    SetScoreTexts {
        value: Vec<StyledText>,
    },
    SetMeasureTexts {
        part: usize,
        staff: usize,
        measure: usize,
        value: Vec<StyledText>,
    },
    SetFiguredBass {
        part: usize,
        staff: usize,
        measure: usize,
        value: Vec<FiguredBassFigure>,
    },
    SetHarpPedalDiagrams {
        part: usize,
        staff: usize,
        measure: usize,
        value: Vec<HarpPedalDiagram>,
    },
    SetChordDefinitions {
        value: Vec<ChordDefinition>,
    },
    SetPartNames {
        part: usize,
        name: String,
        short_name: String,
    },
    SetPartMidi {
        part: usize,
        channel: u8,
        program: u8,
    },
    SetInstrumentDefinition {
        part: usize,
        value: Option<InstrumentDefinition>,
    },
    SetPartMidiAutomation {
        part: usize,
        pitch_bends: Vec<MidiPitchBend>,
        control_changes: Vec<MidiControlChange>,
        program_changes: Vec<MidiProgramChange>,
        aftertouch: Vec<MidiAftertouch>,
    },
    SetStaffConfiguration {
        part: usize,
        staff: usize,
        clef: Clef,
        transpose_semitones: i8,
    },
    SetStaffPresentation {
        part: usize,
        staff: usize,
        value: StaffPresentation,
    },
    SetMeasurePresentation {
        part: usize,
        staff: usize,
        measure: usize,
        number: u32,
        clef: Option<Clef>,
        tempo_text: Option<String>,
        navigation: Option<String>,
        expression_text: Option<String>,
        multi_rest_count: Option<u8>,
        system_break: bool,
        page_break: bool,
        #[serde(default)]
        section_break: bool,
    },
    SetTablatureConfig {
        part: usize,
        staff: usize,
        value: Option<TablatureConfig>,
    },
    SetMeasureTablatureChange {
        part: usize,
        staff: usize,
        measure: usize,
        value: Option<TablatureConfig>,
    },
    SetMeasureMidClefs {
        part: usize,
        staff: usize,
        measure: usize,
        value: Vec<MidMeasureClef>,
    },
    SetMetadata {
        field: String,
        value: String,
    },
    SetTempo {
        value: u16,
    },
    SetKeySignature {
        part: usize,
        staff: usize,
        measure: usize,
        value: Option<KeySignature>,
    },
    SetTimeSignature {
        part: usize,
        staff: usize,
        measure: usize,
        value: Option<TimeSignature>,
    },
    SetBarlines {
        part: usize,
        staff: usize,
        measure: usize,
        left: Barline,
        right: Barline,
    },
    SetRehearsal {
        part: usize,
        staff: usize,
        measure: usize,
        value: Option<String>,
    },
    SetVolta {
        part: usize,
        staff: usize,
        measure: usize,
        value: Option<VoltaBracket>,
    },
    /// Insert `note` at `note_index` in the given voice (existing notes shift right).
    AddNote {
        part: usize,
        staff: usize,
        measure: usize,
        voice: usize,
        /// Position for insertion. `usize::MAX` is the legacy append sentinel.
        #[serde(default = "legacy_append_index")]
        note_index: usize,
        note: Box<Note>,
    },
    RemoveNote {
        part: usize,
        staff: usize,
        measure: usize,
        voice: usize,
        note_index: usize,
    },
    /// Replace the note at `note_index` with `note`.
    ReplaceNote {
        part: usize,
        staff: usize,
        measure: usize,
        voice: usize,
        note_index: usize,
        note: Box<Note>,
    },
    SetMeasureTempo {
        part: usize,
        staff: usize,
        measure: usize,
        value: Option<u16>,
    },
    SetMeasureTempoRamp {
        part: usize,
        staff: usize,
        measure: usize,
        value: Option<u16>,
    },
    /// Replace the complete score when a change cannot be represented safely by
    /// positional operations (for example, a part or measure was added).
    ReplaceScore {
        score: Box<Score>,
    },
}

fn legacy_append_index() -> usize {
    usize::MAX
}

/// Return whether positional patches would lose score data. The patch format deliberately
/// keeps the common editing operations small; fields without a dedicated operation use the
/// complete-score fallback so an interchange round-trip never silently drops notation.
fn patch_requires_replace(a: &Score, b: &Score) -> bool {
    if a.settings.time_signature != b.settings.time_signature
        || a.settings.key_signature != b.settings.key_signature
        || a.parts.len() != b.parts.len()
        || a.part_groups.len() != b.part_groups.len()
    {
        return true;
    }
    if a.part_groups.iter().zip(&b.part_groups).any(|(x, y)| {
        x.first_part != y.first_part
            || x.last_part != y.last_part
            || x.symbol != y.symbol
            || x.barlines_connect != y.barlines_connect
    }) {
        return true;
    }
    for (ap, bp) in a.parts.iter().zip(&b.parts) {
        if ap.percussion_instruments != bp.percussion_instruments
            || ap.staff_groups != bp.staff_groups
            || ap.staves.len() != bp.staves.len()
        {
            return true;
        }
        for (as_, bs) in ap.staves.iter().zip(&bp.staves) {
            if as_.measures.len() != bs.measures.len() {
                return true;
            }
        }
    }
    false
}

/// Compare two scores and return a list of [`ScorePatch`] operations.
///
/// Applying the patches to `a` via [`apply_patch`] produces a score structurally
/// equivalent to `b` (same parts, staves, measures, and note content).
pub fn score_patch(a: &Score, b: &Score) -> Vec<ScorePatch> {
    let mut patches: Vec<ScorePatch> = Vec::new();

    if patch_requires_replace(a, b) {
        return vec![ScorePatch::ReplaceScore {
            score: Box::new(b.clone()),
        }];
    }

    if a.views != b.views {
        patches.push(ScorePatch::SetScoreViews {
            value: b.views.clone(),
        });
    }

    if a.texts != b.texts {
        patches.push(ScorePatch::SetScoreTexts {
            value: b.texts.clone(),
        });
    }
    if a.chord_definitions != b.chord_definitions {
        patches.push(ScorePatch::SetChordDefinitions {
            value: b.chord_definitions.clone(),
        });
    }

    macro_rules! meta {
        ($field:ident, $name:literal) => {
            if a.metadata.$field != b.metadata.$field {
                patches.push(ScorePatch::SetMetadata {
                    field: $name.to_string(),
                    value: b.metadata.$field.clone(),
                });
            }
        };
    }
    meta!(title, "title");
    meta!(composer, "composer");
    meta!(lyricist, "lyricist");
    meta!(copyright, "copyright");
    meta!(work_number, "work_number");
    meta!(movement_title, "movement_title");

    if a.settings.tempo_bpm != b.settings.tempo_bpm {
        patches.push(ScorePatch::SetTempo {
            value: b.settings.tempo_bpm,
        });
    }

    for pi in 0..a.parts.len().min(b.parts.len()) {
        let ap = &a.parts[pi];
        let bp = &b.parts[pi];
        if ap.name != bp.name || ap.short_name != bp.short_name {
            patches.push(ScorePatch::SetPartNames {
                part: pi,
                name: bp.name.clone(),
                short_name: bp.short_name.clone(),
            });
        }
        if ap.midi_channel != bp.midi_channel || ap.midi_program != bp.midi_program {
            patches.push(ScorePatch::SetPartMidi {
                part: pi,
                channel: bp.midi_channel,
                program: bp.midi_program,
            });
        }
        if ap.instrument != bp.instrument {
            patches.push(ScorePatch::SetInstrumentDefinition {
                part: pi,
                value: bp.instrument.clone(),
            });
        }
        if ap.midi_pitch_bends != bp.midi_pitch_bends
            || ap.midi_control_changes != bp.midi_control_changes
            || ap.midi_program_changes != bp.midi_program_changes
            || ap.midi_aftertouch != bp.midi_aftertouch
        {
            patches.push(ScorePatch::SetPartMidiAutomation {
                part: pi,
                pitch_bends: bp.midi_pitch_bends.clone(),
                control_changes: bp.midi_control_changes.clone(),
                program_changes: bp.midi_program_changes.clone(),
                aftertouch: bp.midi_aftertouch.clone(),
            });
        }
        for si in 0..ap.staves.len().min(bp.staves.len()) {
            let a_staff = &ap.staves[si];
            let b_staff = &bp.staves[si];
            if a_staff.clef != b_staff.clef
                || a_staff.transpose_semitones != b_staff.transpose_semitones
            {
                patches.push(ScorePatch::SetStaffConfiguration {
                    part: pi,
                    staff: si,
                    clef: b_staff.clef.clone(),
                    transpose_semitones: b_staff.transpose_semitones,
                });
            }
            if a_staff.tablature != b_staff.tablature {
                patches.push(ScorePatch::SetTablatureConfig {
                    part: pi,
                    staff: si,
                    value: b_staff.tablature.clone(),
                });
            }
            if a_staff.presentation != b_staff.presentation {
                patches.push(ScorePatch::SetStaffPresentation {
                    part: pi,
                    staff: si,
                    value: b_staff.presentation.clone(),
                });
            }
            for mi in 0..a_staff.measures.len().min(b_staff.measures.len()) {
                let am = &a_staff.measures[mi];
                let bm = &b_staff.measures[mi];

                if am.tablature_change != bm.tablature_change {
                    patches.push(ScorePatch::SetMeasureTablatureChange {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.tablature_change.clone(),
                    });
                }

                if am.mid_clefs != bm.mid_clefs {
                    patches.push(ScorePatch::SetMeasureMidClefs {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.mid_clefs.clone(),
                    });
                }

                if am.number != bm.number
                    || am.clef != bm.clef
                    || am.tempo_text != bm.tempo_text
                    || am.navigation != bm.navigation
                    || am.expression_text != bm.expression_text
                    || am.multi_rest_count != bm.multi_rest_count
                    || am.system_break != bm.system_break
                    || am.page_break != bm.page_break
                    || am.section_break != bm.section_break
                {
                    patches.push(ScorePatch::SetMeasurePresentation {
                        part: pi,
                        staff: si,
                        measure: mi,
                        number: bm.number,
                        clef: bm.clef.clone(),
                        tempo_text: bm.tempo_text.clone(),
                        navigation: bm.navigation.clone(),
                        expression_text: bm.expression_text.clone(),
                        multi_rest_count: bm.multi_rest_count,
                        system_break: bm.system_break,
                        page_break: bm.page_break,
                        section_break: bm.section_break,
                    });
                }
                if am.key_sig != bm.key_sig {
                    patches.push(ScorePatch::SetKeySignature {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.key_sig.clone(),
                    });
                }
                if am.time_sig != bm.time_sig {
                    patches.push(ScorePatch::SetTimeSignature {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.time_sig.clone(),
                    });
                }
                if am.barline_left != bm.barline_left || am.barline_right != bm.barline_right {
                    patches.push(ScorePatch::SetBarlines {
                        part: pi,
                        staff: si,
                        measure: mi,
                        left: bm.barline_left.clone(),
                        right: bm.barline_right.clone(),
                    });
                }
                if am.rehearsal != bm.rehearsal {
                    patches.push(ScorePatch::SetRehearsal {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.rehearsal.clone(),
                    });
                }
                if am.volta != bm.volta {
                    patches.push(ScorePatch::SetVolta {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.volta.clone(),
                    });
                }
                if am.tempo != bm.tempo {
                    patches.push(ScorePatch::SetMeasureTempo {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.tempo,
                    });
                }
                if am.tempo_ramp_to != bm.tempo_ramp_to {
                    patches.push(ScorePatch::SetMeasureTempoRamp {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.tempo_ramp_to,
                    });
                }
                if am.texts != bm.texts {
                    patches.push(ScorePatch::SetMeasureTexts {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.texts.clone(),
                    });
                }
                if am.figured_bass != bm.figured_bass {
                    patches.push(ScorePatch::SetFiguredBass {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.figured_bass.clone(),
                    });
                }
                if am.harp_pedal_diagrams != bm.harp_pedal_diagrams {
                    patches.push(ScorePatch::SetHarpPedalDiagrams {
                        part: pi,
                        staff: si,
                        measure: mi,
                        value: bm.harp_pedal_diagrams.clone(),
                    });
                }

                for vi in 0..4usize {
                    let av = &am.voices[vi];
                    let bv = &bm.voices[vi];
                    for (ni, (a_note, b_note)) in av.iter().zip(bv.iter()).enumerate() {
                        if !note_content_eq(a_note, b_note) {
                            patches.push(ScorePatch::ReplaceNote {
                                part: pi,
                                staff: si,
                                measure: mi,
                                voice: vi,
                                note_index: ni,
                                note: Box::new(b_note.clone()),
                            });
                        }
                    }
                    // Notes in `a` beyond `b` — remove in reverse order to preserve indices.
                    for ni in (bv.len()..av.len()).rev() {
                        patches.push(ScorePatch::RemoveNote {
                            part: pi,
                            staff: si,
                            measure: mi,
                            voice: vi,
                            note_index: ni,
                        });
                    }
                    // Notes in `b` beyond `a` — append.
                    for (offset, note) in bv.iter().skip(av.len()).enumerate() {
                        patches.push(ScorePatch::AddNote {
                            part: pi,
                            staff: si,
                            measure: mi,
                            voice: vi,
                            note_index: av.len() + offset,
                            note: Box::new(note.clone()),
                        });
                    }
                }
            }
        }
    }

    patches
}

/// Apply a list of [`ScorePatch`] operations to a cloned copy of `score`.
///
/// Returns `Err(Error::InvalidPatch)` if any patch references an out-of-bounds index.
/// The returned score is an independent clone — `score` is not modified.
pub fn apply_patch(score: &Score, patches: &[ScorePatch]) -> Result<Score, Error> {
    let mut s = score.clone();
    for patch in patches {
        match patch {
            ScorePatch::ReplaceScore { score } => {
                s = (**score).clone();
            }
            ScorePatch::SetScoreViews { value } => {
                s.views = value.clone();
            }
            ScorePatch::SetScoreTexts { value } => {
                s.texts = value.clone();
            }
            ScorePatch::SetMeasureTexts {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .texts = value.clone();
            }
            ScorePatch::SetFiguredBass {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .figured_bass = value.clone();
            }
            ScorePatch::SetHarpPedalDiagrams {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .harp_pedal_diagrams = value.clone();
            }
            ScorePatch::SetChordDefinitions { value } => {
                s.chord_definitions = value.clone();
            }
            ScorePatch::SetPartNames {
                part,
                name,
                short_name,
            } => {
                let target = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?;
                target.name = name.clone();
                target.short_name = short_name.clone();
            }
            ScorePatch::SetPartMidi {
                part,
                channel,
                program,
            } => {
                let target = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?;
                target.midi_channel = *channel;
                target.midi_program = *program;
            }
            ScorePatch::SetInstrumentDefinition { part, value } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .instrument = value.clone();
            }
            ScorePatch::SetPartMidiAutomation {
                part,
                pitch_bends,
                control_changes,
                program_changes,
                aftertouch,
            } => {
                let target = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?;
                target.midi_pitch_bends = pitch_bends.clone();
                target.midi_control_changes = control_changes.clone();
                target.midi_program_changes = program_changes.clone();
                target.midi_aftertouch = aftertouch.clone();
            }
            ScorePatch::SetStaffConfiguration {
                part,
                staff,
                clef,
                transpose_semitones,
            } => {
                let target = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?;
                target.clef = clef.clone();
                target.transpose_semitones = *transpose_semitones;
            }
            ScorePatch::SetStaffPresentation { part, staff, value } => {
                let target = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?;
                target.presentation = value.clone();
            }
            ScorePatch::SetMeasurePresentation {
                part,
                staff,
                measure,
                number,
                clef,
                tempo_text,
                navigation,
                expression_text,
                multi_rest_count,
                system_break,
                page_break,
                section_break,
            } => {
                let target = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| {
                        Error::InvalidPatch(format!("measure {measure} out of range"))
                    })?;
                target.number = *number;
                target.clef = clef.clone();
                target.tempo_text = tempo_text.clone();
                target.navigation = navigation.clone();
                target.expression_text = expression_text.clone();
                target.multi_rest_count = *multi_rest_count;
                target.system_break = *system_break;
                target.page_break = *page_break;
                target.section_break = *section_break;
            }
            ScorePatch::SetTablatureConfig { part, staff, value } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .tablature = value.clone();
            }
            ScorePatch::SetMeasureTablatureChange {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .tablature_change = value.clone();
            }
            ScorePatch::SetMeasureMidClefs {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .mid_clefs = value.clone();
            }
            ScorePatch::SetMetadata { field, value } => match field.as_str() {
                "title" => s.metadata.title = value.clone(),
                "composer" => s.metadata.composer = value.clone(),
                "lyricist" => s.metadata.lyricist = value.clone(),
                "copyright" => s.metadata.copyright = value.clone(),
                "work_number" => s.metadata.work_number = value.clone(),
                "movement_title" => s.metadata.movement_title = value.clone(),
                other => {
                    return Err(Error::InvalidPatch(format!(
                        "unknown metadata field: {other}"
                    )));
                }
            },
            ScorePatch::SetTempo { value } => {
                s.settings.tempo_bpm = *value;
            }
            ScorePatch::SetKeySignature {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .key_sig = value.clone();
            }
            ScorePatch::SetTimeSignature {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .time_sig = value.clone();
            }
            ScorePatch::SetBarlines {
                part,
                staff,
                measure,
                left,
                right,
            } => {
                let m = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| {
                        Error::InvalidPatch(format!("measure {measure} out of range"))
                    })?;
                m.barline_left = left.clone();
                m.barline_right = right.clone();
            }
            ScorePatch::SetRehearsal {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .rehearsal = value.clone();
            }
            ScorePatch::SetVolta {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .volta = value.clone();
            }
            ScorePatch::AddNote {
                part,
                staff,
                measure,
                voice,
                note_index,
                note,
            } => {
                let v = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .voices
                    .get_mut(*voice)
                    .ok_or_else(|| Error::InvalidPatch(format!("voice {voice} out of range")))?;
                let insert_at = if *note_index == usize::MAX {
                    v.len()
                } else {
                    *note_index
                };
                if insert_at > v.len() {
                    return Err(Error::InvalidPatch(format!(
                        "note_index {note_index} out of range"
                    )));
                }
                v.insert(insert_at, *note.clone());
            }
            ScorePatch::RemoveNote {
                part,
                staff,
                measure,
                voice,
                note_index,
            } => {
                let v = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .voices
                    .get_mut(*voice)
                    .ok_or_else(|| Error::InvalidPatch(format!("voice {voice} out of range")))?;
                if *note_index >= v.len() {
                    return Err(Error::InvalidPatch(format!(
                        "note_index {note_index} out of range"
                    )));
                }
                v.remove(*note_index);
            }
            ScorePatch::ReplaceNote {
                part,
                staff,
                measure,
                voice,
                note_index,
                note,
            } => {
                let v = s
                    .parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .voices
                    .get_mut(*voice)
                    .ok_or_else(|| Error::InvalidPatch(format!("voice {voice} out of range")))?;
                if *note_index >= v.len() {
                    return Err(Error::InvalidPatch(format!(
                        "note_index {note_index} out of range"
                    )));
                }
                v[*note_index] = *note.clone();
            }
            ScorePatch::SetMeasureTempo {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .tempo = *value;
            }
            ScorePatch::SetMeasureTempoRamp {
                part,
                staff,
                measure,
                value,
            } => {
                s.parts
                    .get_mut(*part)
                    .ok_or_else(|| Error::InvalidPatch(format!("part {part} out of range")))?
                    .staves
                    .get_mut(*staff)
                    .ok_or_else(|| Error::InvalidPatch(format!("staff {staff} out of range")))?
                    .measures
                    .get_mut(*measure)
                    .ok_or_else(|| Error::InvalidPatch(format!("measure {measure} out of range")))?
                    .tempo_ramp_to = *value;
            }
        }
    }
    if !super::validate::validate(&s).is_valid() {
        return Err(Error::InvalidScore);
    }
    Ok(s)
}

/// Beats a voice occupies in a measure lasting `measure_beats`. A voice holding only one plain
/// whole rest is a measure rest and lasts exactly the measure in any time signature (as in
/// MusicXML and MuseScore); otherwise the voice lasts the sum of its notes.
pub fn voice_duration_beats(voice: &[Note], measure_beats: f64) -> f64 {
    match voice {
        [only] if only.is_plain_whole_rest() => measure_beats,
        _ => voice.iter().map(Note::beats).sum(),
    }
}

/// Respell all pitches in the score to prefer flats or sharps.
///
/// Applies [`Pitch::respell`] to every note in every part, staff, measure, and voice.
pub fn respell_score(score: &mut Score, prefer_flat: bool) {
    for part in &mut score.parts {
        for staff in &mut part.staves {
            for measure in &mut staff.measures {
                for voice in &mut measure.voices {
                    for note in voice.iter_mut() {
                        for pitch in &mut note.pitches {
                            *pitch = pitch.respell(prefer_flat);
                        }
                    }
                }
            }
        }
    }
}

/// Spelling policy for [`respell_staff_region`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum RespellPolicy {
    /// Spell black-key pitches with flats.
    Flat,
    /// Spell black-key pitches with sharps.
    Sharp,
    /// Follow the key signature in effect at each measure: flat keys use flats, others sharps.
    Key,
}

/// Respell the pitched notes of one staff in the measure range `start_measure..end_measure`
/// (end exclusive), the selection form of [`respell_score`].
///
/// With [`RespellPolicy::Key`], each measure uses its own key change, then the part's first-staff
/// key change, then the score key. Rests and unpitched notes are left unchanged, because an
/// unpitched note's pitch is its staff position. Sounding pitch and microtones never change.
///
/// A tie never joins two spellings: a tied chain takes the spelling of its first note inside the
/// range, including chain members before or after the range. Returns the inclusive measure span
/// that changed, which is wider than the range when a tie crosses its boundary.
pub fn respell_staff_region(
    score: &mut Score,
    part_index: usize,
    staff_index: usize,
    start_measure: usize,
    end_measure: usize,
    policy: RespellPolicy,
) -> Result<(usize, usize), Error> {
    let score_key_flat = score.settings.key_signature.fifths < 0;
    let part = score
        .parts
        .get_mut(part_index)
        .ok_or(Error::PartNotFound(part_index))?;
    let staff_count = part.staves.len();
    if staff_index >= staff_count {
        return Err(Error::StaffNotFound(staff_index));
    }
    let measure_count = part.staves[staff_index].measures.len();
    if start_measure >= end_measure || end_measure > measure_count {
        return Err(Error::InvalidCommand(format!(
            "invalid measure range {start_measure}..{end_measure}"
        )));
    }
    let mut prefer_flat = Vec::with_capacity(end_measure);
    let mut running_flat = score_key_flat;
    for index in 0..end_measure {
        let key = part.staves[staff_index].measures[index]
            .key_sig
            .as_ref()
            .or_else(|| {
                part.staves[0]
                    .measures
                    .get(index)
                    .and_then(|measure| measure.key_sig.as_ref())
            });
        if let Some(key) = key {
            running_flat = key.fifths < 0;
        }
        prefer_flat.push(match policy {
            RespellPolicy::Flat => true,
            RespellPolicy::Sharp => false,
            RespellPolicy::Key => running_flat,
        });
    }

    let measures = &mut part.staves[staff_index].measures;
    for (index, measure) in measures
        .iter_mut()
        .enumerate()
        .take(end_measure)
        .skip(start_measure)
    {
        for voice in &mut measure.voices {
            for note in voice
                .iter_mut()
                .filter(|note| !note.is_rest && !note.is_unpitched)
            {
                for pitch in &mut note.pitches {
                    *pitch = pitch.respell(prefer_flat[index]);
                }
            }
        }
    }

    let mut changed = (start_measure, end_measure - 1);
    for voice in 0..4 {
        for measure in start_measure..end_measure {
            for note in 0..measures[measure].voices[voice].len() {
                if measures[measure].voices[voice][note].tie_start {
                    let last = propagate_tied_spelling(measures, voice, (measure, note), true);
                    changed.1 = changed.1.max(last);
                }
            }
        }
        if !measures[start_measure].voices[voice].is_empty() {
            let first = propagate_tied_spelling(measures, voice, (start_measure, 0), false);
            changed.0 = changed.0.min(first);
        }
    }
    Ok(changed)
}

/// Copy one note's spelling along its tie chain (forward through `tie_start`, or backward through
/// `tie_end`), matching chord members by sounding pitch. Returns the last measure reached.
fn propagate_tied_spelling(
    measures: &mut [Measure],
    voice: usize,
    from: (usize, usize),
    forward: bool,
) -> usize {
    let mut current = from;
    loop {
        let note = &measures[current.0].voices[voice][current.1];
        if !(if forward {
            note.tie_start
        } else {
            note.tie_end
        }) {
            return current.0;
        }
        let neighbor = if forward {
            if current.1 + 1 < measures[current.0].voices[voice].len() {
                Some((current.0, current.1 + 1))
            } else {
                measures
                    .get(current.0 + 1)
                    .filter(|measure| !measure.voices[voice].is_empty())
                    .map(|_| (current.0 + 1, 0))
            }
        } else if current.1 > 0 {
            Some((current.0, current.1 - 1))
        } else {
            current.0.checked_sub(1).and_then(|previous| {
                measures[previous].voices[voice]
                    .len()
                    .checked_sub(1)
                    .map(|last| (previous, last))
            })
        };
        let Some(next) = neighbor else {
            return current.0;
        };
        let next_note = &measures[next.0].voices[voice][next.1];
        if !(if forward {
            next_note.tie_end
        } else {
            next_note.tie_start
        }) {
            return current.0;
        }
        let source = measures[current.0].voices[voice][current.1].pitches.clone();
        for pitch in &mut measures[next.0].voices[voice][next.1].pitches {
            if let Some(spelled) = source.iter().find(|candidate| {
                candidate.to_midi() == pitch.to_midi()
                    && candidate.microtone_cents == pitch.microtone_cents
            }) {
                *pitch = spelled.clone();
            }
        }
        current = next;
    }
}

/// Respell all pitches to match the score's key signature spelling convention.
///
/// Flat-key signatures (fifths < 0) use flat spellings; sharp-key and C major use sharps.
pub fn respell_score_to_key(score: &mut Score) {
    let prefer_flat = score.settings.key_signature.fifths < 0;
    respell_score(score, prefer_flat);
}

/// Compute total playback duration in seconds.
///
/// Uses `measure_sequence` for correct repeat handling. Lighter than generating
/// full playback events — suitable for progress bars and UI display.
pub fn score_duration_secs(score: &Score) -> f64 {
    if score.settings.tempo_bpm == 0 {
        return 0.0;
    }
    let seq = measure_sequence(score);
    let mut total_secs = 0.0f64;
    let mut current_bpm = score.settings.tempo_bpm as f64;
    if let Some(staff) = score.parts.first().and_then(|p| p.staves.first()) {
        for &idx in &seq {
            if let Some(m) = staff.measures.get(idx) {
                if let Some(b) = m.tempo {
                    current_bpm = b as f64;
                }
                if current_bpm == 0.0 {
                    continue;
                }
                let beats = voice_duration_beats(
                    &m.voices[0],
                    staff.measure_beats(idx, &score.settings.time_signature),
                );
                total_secs += tempo_ramp_duration_secs(current_bpm, m.tempo_ramp_to, beats);
                if let Some(target) = m.tempo_ramp_to.filter(|target| *target > 0) {
                    current_bpm = f64::from(target);
                }
            }
        }
    }
    total_secs
}

/// Compute playback duration in seconds for a specific measure range (inclusive).
///
/// `region` is `(start_measure, end_measure)`, both 0-based. Measures outside the range
/// are excluded. Uses `measure_sequence` for correct repeat handling.
pub fn score_duration_secs_region(score: &Score, region: (usize, usize)) -> f64 {
    if score.settings.tempo_bpm == 0 {
        return 0.0;
    }
    let seq: Vec<usize> = measure_sequence(score)
        .into_iter()
        .filter(|&idx| idx >= region.0 && idx <= region.1)
        .collect();
    let mut total_secs = 0.0f64;
    let mut current_bpm = score.settings.tempo_bpm as f64;
    if let Some(staff) = score.parts.first().and_then(|p| p.staves.first()) {
        for &idx in &seq {
            if let Some(m) = staff.measures.get(idx) {
                if let Some(b) = m.tempo {
                    current_bpm = b as f64;
                }
                if current_bpm == 0.0 {
                    continue;
                }
                let beats = voice_duration_beats(
                    &m.voices[0],
                    staff.measure_beats(idx, &score.settings.time_signature),
                );
                total_secs += tempo_ramp_duration_secs(current_bpm, m.tempo_ramp_to, beats);
                if let Some(target) = m.tempo_ramp_to.filter(|target| *target > 0) {
                    current_bpm = f64::from(target);
                }
            }
        }
    }
    total_secs
}

fn tempo_ramp_duration_secs(start_bpm: f64, target_bpm: Option<u16>, beats: f64) -> f64 {
    let Some(target_bpm) = target_bpm.filter(|target| *target > 0) else {
        return beats / start_bpm * 60.0;
    };
    let end_bpm = f64::from(target_bpm);
    let delta = end_bpm - start_bpm;
    if delta.abs() < f64::EPSILON {
        return beats / start_bpm * 60.0;
    }
    60.0 * beats / delta * (end_bpm / start_bpm).ln()
}

/// Return the number of beats available in a voice before it is full.
///
/// Uses [`Note::beats`] which correctly handles tuplet scaling.
/// Returns `Ok(0.0)` when the voice is already full or over-full.
pub fn measure_beats_remaining(
    score: &Score,
    part_index: usize,
    staff_index: usize,
    measure_index: usize,
    voice_index: usize,
) -> Result<f64, Error> {
    let part = score
        .parts
        .get(part_index)
        .ok_or(Error::PartNotFound(part_index))?;
    let staff = part
        .staves
        .get(staff_index)
        .ok_or(Error::StaffNotFound(staff_index))?;
    let measure = staff
        .measures
        .get(measure_index)
        .ok_or(Error::MeasureNotFound(measure_index))?;
    let voice = measure
        .voices
        .get(voice_index)
        .ok_or(Error::VoiceOutOfRange(voice_index))?;
    let capacity = staff.measure_beats(measure_index, &score.settings.time_signature);
    Ok((capacity - voice_duration_beats(voice, capacity)).max(0.0))
}

/// Suggest whether the stem should point up for the given pitches and clef.
///
/// Conventional rule: if the average MIDI pitch of the chord is below the staff
/// middle line, the stem points up; at or above, it points down.
/// For empty pitch lists (rests), returns `true` by convention.
pub fn suggested_stem_up(pitches: &[Pitch], clef: &Clef) -> bool {
    if pitches.is_empty() {
        return true;
    }
    let avg = pitches.iter().map(|p| p.to_midi() as f64).sum::<f64>() / pitches.len() as f64;
    avg < clef.middle_line_midi() as f64
}

fn beam_beat_size(ts: &TimeSignature) -> f64 {
    if ts.numerator.is_multiple_of(3) && ts.numerator >= 6 && ts.denominator >= 8 {
        3.0 * 4.0 / ts.denominator as f64
    } else {
        4.0 / ts.denominator as f64
    }
}

/// Compute recommended [`BeamState`] values for a voice's notes.
///
/// Groups beamable notes (eighth or shorter, non-rest) within beat boundaries.
/// Returns a `Vec` the same length as `notes`.
pub fn compute_beams(notes: &[Note], time_sig: &TimeSignature) -> Vec<BeamState> {
    let beat_size = beam_beat_size(time_sig);
    let n = notes.len();
    let mut result = vec![BeamState::None; n];

    let is_beamable = |note: &Note| -> bool {
        !note.is_rest
            && matches!(
                note.duration,
                Duration::Eighth
                    | Duration::Sixteenth
                    | Duration::ThirtySecond
                    | Duration::SixtyFourth
                    | Duration::HundredTwentyEighth
            )
    };

    // Compute beat start positions
    let mut starts = Vec::with_capacity(n);
    let mut pos = 0.0f64;
    for note in notes {
        starts.push(pos);
        pos += note.beats();
    }

    // A tuplet can end exactly on a beat while the accumulated f64 start is a
    // few ulps below it (15 copies of 1/15, for example). Snap only starts
    // within a much smaller interval than any supported note value.
    let group_id = |i: usize| -> i64 {
        let beat = starts[i] / beat_size;
        let nearest = beat.round();
        if (beat - nearest).abs() <= 1e-9 {
            nearest as i64
        } else {
            beat.floor() as i64
        }
    };

    let mut i = 0;
    while i < n {
        if !is_beamable(&notes[i]) {
            i += 1;
            continue;
        }
        let g = group_id(i);
        // Find the run of beamable notes in the same beat group
        let mut j = i;
        while j < n && is_beamable(&notes[j]) && group_id(j) == g {
            j += 1;
        }
        let run = j - i;
        if run == 1 {
            result[i] = BeamState::None;
        } else {
            result[i] = BeamState::Begin;
            result[i + 1..j - 1].fill(BeamState::Continue);
            result[j - 1] = BeamState::End;
        }
        i = j;
    }
    result
}

fn note_content_eq(a: &Note, b: &Note) -> bool {
    a.is_rest == b.is_rest
        && a.is_unpitched == b.is_unpitched
        && a.instrument_id == b.instrument_id
        && a.offset_x == b.offset_x
        && a.offset_y == b.offset_y
        && a.relative_x == b.relative_x
        && a.relative_y == b.relative_y
        && a.pitches == b.pitches
        && a.duration == b.duration
        && a.dot_count == b.dot_count
        && a.tie_start == b.tie_start
        && a.tie_end == b.tie_end
        && a.beam == b.beam
        && a.articulations == b.articulations
        && a.dynamic == b.dynamic
        && a.stem_up == b.stem_up
        && a.hairpin_start == b.hairpin_start
        && a.hairpin_end == b.hairpin_end
        && a.tuplet == b.tuplet
        && a.chord_symbol == b.chord_symbol
        && a.is_grace == b.is_grace
        && a.grace_slash == b.grace_slash
        && a.ottava_start == b.ottava_start
        && a.ottava_end == b.ottava_end
        && a.lyric == b.lyric
        && a.additional_lyrics == b.additional_lyrics
        && a.pedal_start == b.pedal_start
        && a.pedal_end == b.pedal_end
        && a.slur_start == b.slur_start
        && a.slur_end == b.slur_end
        && a.arpeggiate == b.arpeggiate
        && a.tab_position == b.tab_position
        && a.tab_positions == b.tab_positions
        && a.guitar_technique == b.guitar_technique
        && a.guitar_bend_alter_cents == b.guitar_bend_alter_cents
        && a.guitar_bend_curve == b.guitar_bend_curve
}

fn per_pitch_flag(flags: &[bool], pitch_count: usize, index: usize, chord: bool) -> bool {
    if flags.len() == pitch_count {
        flags.get(index).copied().unwrap_or(chord)
    } else {
        chord
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::model::{
        notation::{FingeringSelectionPolicy, TextStyle},
        pitch::Step,
    };

    #[test]
    fn fingering_selection_policy_is_deterministic_and_non_mutating() {
        let mut note = Note::new(Pitch::new(Step::C, 4), Duration::Quarter);
        note.fingerings = vec![3, 1, 4];
        note.fingering = Some(3);
        assert_eq!(
            note.select_fingering(FingeringSelectionPolicy::SourceOrder),
            Some(3)
        );
        assert_eq!(
            note.select_fingering(FingeringSelectionPolicy::LowestNumber),
            Some(1)
        );
        assert_eq!(
            note.select_fingering(FingeringSelectionPolicy::HighestNumber),
            Some(4)
        );
        assert_eq!(note.fingerings, vec![3, 1, 4]);
        assert_eq!(note.fingering, Some(3));
    }

    #[test]
    fn default_score_has_one_part_four_measures() {
        let score = Score::default();
        assert_eq!(score.parts.len(), 1);
        assert_eq!(score.parts[0].staves.len(), 1);
        assert_eq!(score.parts[0].staves[0].measures.len(), 4);
    }

    #[test]
    fn assign_tablature_positions_is_capo_aware_and_preserves_explicit_positions() {
        let mut score = Score::new("Guitar", 120, 4, 4, 0, 1);
        score.parts[0].staves[0].tablature = Some(TablatureConfig {
            lines: 6,
            tuning_midi: vec![64, 59, 55, 50, 45, 40],
            capo: 2,
        });
        score.parts[0].staves[0].measures[0].voices[0].push(Note::new(
            Pitch::with_alter(Step::F, 4, 1),
            Duration::Quarter,
        ));
        score.parts[0].staves[0].measures[0].voices[0]
            .push(Note::new(Pitch::new(Step::G, 3), Duration::Quarter));
        score.parts[0].staves[0].measures[0].voices[0][2].tab_position =
            Some(TabPosition { string: 6, fret: 7 });

        assert_eq!(assign_tablature_positions(&mut score), 1);
        let notes = &score.parts[0].staves[0].measures[0].voices[0];
        assert_eq!(
            notes[1].tab_position,
            Some(TabPosition { string: 1, fret: 0 })
        );
        assert_eq!(notes[1].string_number, Some(1));
        assert_eq!(
            notes[2].tab_position,
            Some(TabPosition { string: 6, fret: 7 })
        );
    }

    #[test]
    fn assign_tablature_positions_uses_measure_local_capo_change() {
        let mut score = Score::new("Guitar", 120, 4, 4, 0, 2);
        score.parts[0].staves[0].tablature = Some(TablatureConfig {
            lines: 6,
            tuning_midi: vec![40, 45, 50, 55, 59, 64],
            capo: 0,
        });
        score.parts[0].staves[0].measures[1].tablature_change = Some(TablatureConfig {
            lines: 6,
            tuning_midi: vec![40, 45, 50, 55, 59, 64],
            capo: 2,
        });
        score.parts[0].staves[0].measures[1].voices[0]
            .push(Note::new(Pitch::new(Step::E, 4), Duration::Quarter));

        assert_eq!(assign_tablature_positions(&mut score), 1);
        assert_eq!(
            score.parts[0].staves[0].measures[1].voices[0][1].tab_position,
            Some(TabPosition { string: 5, fret: 3 })
        );
    }

    #[test]
    fn assign_tablature_positions_optimizes_chord_strings_and_fret_span() {
        let mut score = Score::new("Guitar", 120, 4, 4, 0, 1);
        score.parts[0].staves[0].tablature = Some(TablatureConfig {
            lines: 6,
            tuning_midi: vec![64, 59, 55, 50, 45, 40],
            capo: 0,
        });
        let mut chord = Note::new(Pitch::new(Step::E, 4), Duration::Quarter);
        chord.pitches.push(Pitch::new(Step::G, 4));
        score.parts[0].staves[0].measures[0].voices[0].push(chord);

        assert_eq!(assign_tablature_positions(&mut score), 1);
        let positions = &score.parts[0].staves[0].measures[0].voices[0][1].tab_positions;
        assert_eq!(
            positions,
            &vec![
                TabPosition { string: 2, fret: 5 },
                TabPosition { string: 1, fret: 3 },
            ]
        );
    }

    #[test]
    fn new_score_measure_count() {
        let score = Score::new("Test", 120, 4, 4, 0, 8);
        assert_eq!(score.measure_count(), 8);
    }

    #[test]
    fn note_beats_quarter() {
        let note = Note::new(Pitch::new(Step::C, 4), Duration::Quarter);
        assert!((note.beats() - 1.0).abs() < 1e-9);
    }

    #[test]
    fn note_beats_dotted_quarter() {
        let mut note = Note::new(Pitch::new(Step::C, 4), Duration::Quarter);
        note.dot_count = 1;
        assert!((note.beats() - 1.5).abs() < 1e-9);
    }

    #[test]
    fn grace_note_beats_zero() {
        let mut note = Note::new(Pitch::new(Step::C, 4), Duration::Eighth);
        note.is_grace = true;
        assert_eq!(note.beats(), 0.0);
    }

    #[test]
    fn measure_empty_4_4_fills_four_beats() {
        let m = Measure::empty(4, 4);
        let total: f64 = m.voices[0].iter().map(|n| n.beats()).sum();
        assert!((total - 4.0).abs() < 1e-9);
    }

    #[test]
    fn measure_empty_3_4_fills_three_beats() {
        let m = Measure::empty(3, 4);
        let total: f64 = m.voices[0].iter().map(|n| n.beats()).sum();
        assert!((total - 3.0).abs() < 1e-9);
    }

    #[test]
    fn whole_filling_beats() {
        assert_eq!(Duration::whole_filling_beats(16.0), Duration::Longa);
        assert_eq!(Duration::whole_filling_beats(8.0), Duration::Breve);
        assert_eq!(Duration::whole_filling_beats(4.0), Duration::Whole);
        assert_eq!(Duration::whole_filling_beats(2.0), Duration::Half);
        assert_eq!(Duration::whole_filling_beats(1.0), Duration::Quarter);
    }

    // ── ScoreStats ────────────────────────────────────────────────────────────

    #[test]
    fn statistics_default_score_all_rests() {
        let score = Score::default();
        let s = score.statistics();
        assert_eq!(s.part_count, 1);
        assert_eq!(s.measure_count, 4);
        assert_eq!(s.note_count, 0);
        assert!(s.rest_count > 0);
    }

    #[test]
    fn statistics_duration_estimate() {
        // 4/4, 120 BPM, 1 measure → 4 beats → 2.0 s
        let score = Score::new("T", 120, 4, 4, 0, 1);
        let s = score.statistics();
        assert!((s.estimated_duration_secs - 2.0).abs() < 0.01);
    }

    #[test]
    fn score_duration_secs_matches_statistics() {
        use super::score_duration_secs;
        let score = Score::new("T", 120, 4, 4, 0, 4);
        let secs = score_duration_secs(&score);
        // 4/4, 120 BPM, 4 measures → 16 beats → 8.0 s
        assert!((secs - 8.0).abs() < 0.01, "expected ~8.0 s, got {secs}");
    }

    #[test]
    fn score_duration_secs_integrates_measure_tempo_ramp() {
        use super::score_duration_secs;
        let mut score = Score::new("Ramp", 120, 4, 4, 0, 1);
        score.parts[0].staves[0].measures[0].tempo_ramp_to = Some(60);
        let expected = 4.0 * 60.0 / (60.0 - 120.0) * (60.0f64 / 120.0).ln();
        assert!((score_duration_secs(&score) - expected).abs() < 1e-9);
    }

    #[test]
    fn score_duration_secs_zero_bpm_returns_zero() {
        use super::score_duration_secs;
        let mut score = Score::new("T", 120, 4, 4, 0, 1);
        score.settings.tempo_bpm = 0;
        assert_eq!(score_duration_secs(&score), 0.0);
    }

    #[test]
    fn score_duration_secs_per_measure_tempo() {
        use super::score_duration_secs;
        // 2 measures: measure 0 at 120 BPM (2.0 s), measure 1 at 60 BPM (4.0 s)
        let mut score = Score::new("T", 120, 4, 4, 0, 2);
        score.parts[0].staves[0].measures[1].tempo = Some(60);
        let secs = score_duration_secs(&score);
        assert!((secs - 6.0).abs() < 0.01, "expected ~6.0 s, got {secs}");
    }

    // ── extract_part ──────────────────────────────────────────────────────────

    #[test]
    fn extract_part_returns_single_part_score() {
        let mut score = Score::default();
        let mut p2 = Part::new("Violin", "Vln.");
        p2.staves.push(Staff::new(Clef::Treble));
        score.parts.push(p2);
        let ex = score.extract_part(0).unwrap();
        assert_eq!(ex.parts.len(), 1);
        assert_ne!(ex.id, score.id);
        assert_eq!(ex.metadata.title, score.metadata.title);
    }

    #[test]
    fn extract_part_out_of_range_is_none() {
        let score = Score::default();
        assert!(score.extract_part(99).is_none());
    }

    #[test]
    fn extract_and_merge_remap_typed_spanner_part_addresses() {
        let mut left = Score::template(ScoreTemplate::StringQuartet);
        let address = NoteAddr {
            part: 1,
            staff: 0,
            measure: 0,
            voice: 0,
            note: 0,
        };
        left.spanners.push(NotationSpanner {
            id: "left-span".to_string(),
            kind: NotationSpannerKind::Slur,
            start: address.clone(),
            end: address,
            number: Some(1),
            line_type: None,
            text: None,
            placement: None,
            ottava_size: None,
            ottava_type: None,
        });
        let extracted = left.extract_part_checked(1).expect("valid extracted part");
        assert_eq!(extracted.spanners[0].start.part, 0);
        assert_eq!(extracted.spanners[0].end.part, 0);

        let mut right = Score::new("R", 120, 4, 4, 0, 1);
        let right_address = NoteAddr {
            part: 0,
            staff: 0,
            measure: 0,
            voice: 0,
            note: 0,
        };
        right.spanners.push(NotationSpanner {
            id: "right-span".to_string(),
            kind: NotationSpannerKind::Pedal,
            start: right_address.clone(),
            end: right_address,
            number: Some(1),
            line_type: None,
            text: None,
            placement: None,
            ottava_size: None,
            ottava_type: None,
        });
        let merged = left.merge_checked(&right).expect("valid merged score");
        let right_span = merged
            .spanners
            .iter()
            .find(|spanner| spanner.id == "right-span")
            .expect("merged right span");
        assert_eq!(right_span.start.part, left.parts.len());
        assert_eq!(right_span.end.part, left.parts.len());
    }

    // ── transpose ─────────────────────────────────────────────────────────────

    #[test]
    fn transpose_zero_is_clone() {
        let score = Score::new("T", 120, 4, 4, 0, 1);
        let t = transpose(&score, 0);
        assert_eq!(t.settings.key_signature.fifths, 0);
    }

    #[test]
    fn transpose_staff_region_rewrites_only_selected_written_measures() {
        let mut score = Score::new("T", 120, 4, 4, 0, 2);
        for measure in &mut score.parts[0].staves[0].measures {
            measure.voices[0] = vec![Note::new(Pitch::new(Step::C, 4), Duration::Whole)];
        }
        let transformed = transpose_staff_region_checked(
            &score,
            0,
            0,
            1,
            2,
            2,
            RegionalTranspositionTarget::Written,
        )
        .expect("region should transpose");
        assert_eq!(
            transformed.parts[0].staves[0].measures[0].voices[0][0].pitches[0],
            Pitch::new(Step::C, 4)
        );
        assert_eq!(
            transformed.parts[0].staves[0].measures[1].voices[0][0].pitches[0],
            Pitch::new(Step::D, 4)
        );
        assert_eq!(
            score.parts[0].staves[0].measures[1].voices[0][0].pitches[0],
            Pitch::new(Step::C, 4)
        );
    }

    #[test]
    fn regional_concert_transposition_requires_full_staff() {
        let score = Score::new("T", 120, 4, 4, 0, 2);
        assert!(
            transpose_staff_region_checked(
                &score,
                0,
                0,
                1,
                2,
                -2,
                RegionalTranspositionTarget::Concert,
            )
            .is_err()
        );
    }

    #[test]
    fn transpose_c_major_up_2_to_d_major() {
        let score = Score::new("T", 120, 4, 4, 0, 1);
        assert_eq!(transpose(&score, 2).settings.key_signature.fifths, 2);
    }

    #[test]
    fn transpose_d_major_up_5_to_g_major() {
        let score = Score::new("T", 120, 4, 4, 2, 1);
        assert_eq!(transpose(&score, 5).settings.key_signature.fifths, 1);
    }

    #[test]
    fn transpose_c4_up_1_to_csharp4() {
        let p = transpose_pitch(&Pitch::new(Step::C, 4), 1);
        assert_eq!(p.to_midi(), 61);
        assert_eq!(p.step, Step::C);
        assert_eq!(p.alter, 1);
    }

    #[test]
    fn transpose_c4_down_1_to_b3() {
        let p = transpose_pitch(&Pitch::new(Step::C, 4), -1);
        assert_eq!(p.to_midi(), 59);
        assert_eq!(p.step, Step::B);
        assert_eq!(p.alter, 0);
    }

    #[test]
    fn transpose_up_octave_keeps_step() {
        let p = transpose_pitch(&Pitch::new(Step::A, 4), 12);
        assert_eq!(p.to_midi(), 81);
        assert_eq!(p.step, Step::A);
        assert_eq!(p.octave, 5);
    }

    #[test]
    fn statistics_with_repeat_doubles_duration() {
        // 4/4, 120 BPM, 2 measures with RepeatStart+RepeatEnd → plays twice → 4 measures worth
        let mut score = Score::new("T", 120, 4, 4, 0, 2);
        score.parts[0].staves[0].measures[0].barline_left =
            crate::model::notation::Barline::RepeatStart;
        score.parts[0].staves[0].measures[1].barline_right =
            crate::model::notation::Barline::RepeatEnd;
        let s = score.statistics();
        // 4 beats × 4 measures (2 physical × 2 passes) ÷ 120 BPM × 60 = 8.0 s
        assert!((s.estimated_duration_secs - 8.0).abs() < 0.01);
    }

    #[test]
    fn transpose_octave_boundary_b4_to_c5() {
        // B4 (midi=71) + 1 semitone = C5 (midi=72)
        let p = transpose_pitch(&Pitch::new(Step::B, 4), 1);
        assert_eq!(p.to_midi(), 72);
        assert_eq!(p.step, Step::C);
        assert_eq!(p.octave, 5);
    }

    #[test]
    fn transpose_clamp_at_midi_127() {
        // G9 (midi=127) + 3 semitones → clamped to 127
        let p = transpose_pitch(&Pitch::new(Step::G, 9), 3);
        assert_eq!(p.to_midi(), 127);
    }

    // ── merge ─────────────────────────────────────────────────────────────────

    #[test]
    fn merge_combines_parts() {
        let mut a = Score::new("A", 120, 4, 4, 0, 2);
        let b = Score::new("B", 120, 4, 4, 0, 2);
        // Add a second part to score a
        let mut p2 = Part::new("Violin", "Vln.");
        p2.staves.push(Staff::new(Clef::Treble));
        for i in 0..2usize {
            let mut m = Measure::empty(4, 4);
            m.number = i as u32 + 1;
            p2.staves[0].measures.push(m);
        }
        a.parts.push(p2);
        let merged = a.merge(&b);
        // a has 2 parts, b has 1 part → merged has 3 parts
        assert_eq!(merged.parts.len(), 3);
    }

    #[test]
    fn merge_pads_shorter_score() {
        let a = Score::new("A", 120, 4, 4, 0, 4);
        let b = Score::new("B", 120, 4, 4, 0, 2);
        let merged = a.merge(&b);
        // Both parts should have 4 measures
        assert_eq!(merged.parts[0].staves[0].measures.len(), 4);
        assert_eq!(merged.parts[1].staves[0].measures.len(), 4);
    }

    #[test]
    fn merge_uses_self_metadata() {
        let mut a = Score::new("Title A", 120, 4, 4, 0, 2);
        a.metadata.composer = "Composer A".to_string();
        let b = Score::new("Title B", 120, 4, 4, 0, 2);
        let merged = a.merge(&b);
        assert_eq!(merged.metadata.title, "Title A");
        assert_eq!(merged.metadata.composer, "Composer A");
    }

    #[test]
    fn merge_new_id_differs_from_both() {
        let a = Score::new("A", 120, 4, 4, 0, 2);
        let b = Score::new("B", 120, 4, 4, 0, 2);
        let merged = a.merge(&b);
        assert_ne!(merged.id, a.id);
        assert_ne!(merged.id, b.id);
    }

    // ── Staff.transpose_semitones ─────────────────────────────────────────────

    #[test]
    fn staff_default_transpose_is_zero() {
        let s = Staff::new(Clef::Treble);
        assert_eq!(s.transpose_semitones, 0);
    }

    #[test]
    fn staff_presentation_defaults_and_tracks_percussion_clef() {
        let standard = Staff::new(Clef::Treble);
        assert_eq!(standard.presentation, StaffPresentation::default());

        let percussion = Staff::new(Clef::Percussion);
        assert_eq!(percussion.presentation.kind, StaffKind::Percussion);
        assert_eq!(percussion.presentation.lines, 5);
        assert!(percussion.presentation.visible);
    }

    // ── schema_version ────────────────────────────────────────────────────────

    #[test]
    fn score_default_has_schema_version_1() {
        let score = Score::default();
        assert_eq!(score.schema_version, 1);
    }

    #[test]
    fn score_new_has_schema_version_1() {
        let score = Score::new("T", 120, 4, 4, 0, 4);
        assert_eq!(score.schema_version, 1);
    }

    #[test]
    fn score_without_schema_version_deserializes_to_zero() {
        let json = r#"{"id":"abc","metadata":{"title":"T","composer":"","lyricist":"","copyright":"","work_number":"","movement_title":""},"settings":{"tempo_bpm":120,"time_signature":{"numerator":4,"denominator":4},"key_signature":{"fifths":0,"mode":"major"}},"parts":[]}"#;
        let score: Score = serde_json::from_str(json).unwrap();
        assert_eq!(score.schema_version, 0);
    }

    #[test]
    fn legacy_score_json_defaults_typed_spanners() {
        let score = Score::new("Legacy", 120, 4, 4, 0, 1);
        let mut value = serde_json::to_value(score).expect("score serializes");
        value
            .as_object_mut()
            .expect("score is an object")
            .remove("spanners");
        let restored: Score = serde_json::from_value(value).expect("legacy score deserializes");
        assert!(restored.spanners.is_empty());
    }

    #[test]
    fn legacy_staff_json_defaults_presentation() {
        let score = Score::new("Legacy", 120, 4, 4, 0, 1);
        let mut value = serde_json::to_value(score).expect("score serializes");
        value["parts"][0]["staves"][0]
            .as_object_mut()
            .expect("staff is an object")
            .remove("presentation");

        let restored: Score = serde_json::from_value(value).expect("legacy score deserializes");
        assert_eq!(
            restored.parts[0].staves[0].presentation,
            StaffPresentation::default()
        );
    }

    #[test]
    fn legacy_part_json_defaults_instrument_definition() {
        let score = Score::new("Legacy", 120, 4, 4, 0, 1);
        let mut value = serde_json::to_value(score).expect("score serializes");
        value["parts"][0]
            .as_object_mut()
            .expect("part is an object")
            .remove("instrument");

        let restored: Score = serde_json::from_value(value).expect("legacy score deserializes");
        assert!(restored.parts[0].instrument.is_none());
    }

    #[test]
    fn resolve_view_projects_linked_part_without_mutating_source_score() {
        let mut score = Score::template(ScoreTemplate::StringQuartet);
        let mut view = ScoreView::linked_part("violin-2", "Violin II", 1);
        view.layout.measures_per_row = Some(2);
        score.views.push(view);

        let projected = score.resolve_view("violin-2").expect("view resolves");
        assert_eq!(projected.parts.len(), 1);
        assert_eq!(projected.parts[0].name, "Violin II");
        assert_eq!(projected.views.len(), 1);
        assert_eq!(projected.views[0].parts, vec![0]);
        assert_eq!(score.parts.len(), 4);
        assert_eq!(score.views[0].parts, vec![1]);
    }

    #[test]
    fn resolve_view_applies_linked_standard_and_tablature_presentations_non_destructively() {
        let mut score = Score::new("Guitar", 120, 4, 4, 0, 1);
        score.parts[0].staves[0].tablature = Some(TablatureConfig {
            lines: 6,
            tuning_midi: vec![40, 45, 50, 55, 59, 64],
            capo: 0,
        });
        score.parts[0].staves[0].presentation.kind = StaffKind::Standard;
        score.views.push(ScoreView::linked_tablature_staff(
            "guitar-tab",
            "Guitar Tab",
            0,
            0,
        ));

        let projected = score.resolve_view("guitar-tab").expect("view resolves");
        assert_eq!(
            projected.parts[0].staves[0].presentation.kind,
            StaffKind::Tablature
        );
        assert_eq!(
            projected.views[0].staff_kind_overrides[0].staff,
            ViewStaffRef { part: 0, staff: 0 }
        );
        assert_eq!(
            score.parts[0].staves[0].presentation.kind,
            StaffKind::Standard
        );
    }

    #[test]
    fn legacy_score_view_json_defaults_staff_kind_overrides() {
        let mut score = Score::new("Legacy", 120, 4, 4, 0, 1);
        score.views.push(ScoreView::linked_part("part", "Part", 0));
        let mut value = serde_json::to_value(score).expect("score serializes");
        value["views"][0]
            .as_object_mut()
            .expect("view is an object")
            .remove("staff_kind_overrides");

        let restored: Score = serde_json::from_value(value).expect("legacy score deserializes");
        assert!(restored.views[0].staff_kind_overrides.is_empty());
    }

    #[test]
    fn typed_view_style_overrides_are_ordered_and_json_compatible() {
        let mut view = ScoreView::linked_part("part", "Part", 0);
        view.layout.typed_style_overrides = vec![
            ViewStyleOverride {
                property: ViewStyleProperty::TextScale,
                value: 0.9,
            },
            ViewStyleOverride {
                property: ViewStyleProperty::TextScale,
                value: 1.1,
            },
        ];
        assert_eq!(
            view.layout.style_value(ViewStyleProperty::TextScale),
            Some(1.1)
        );
        let restored: ScoreView =
            serde_json::from_str(&serde_json::to_string(&view).unwrap()).unwrap();
        assert_eq!(
            restored.layout.typed_style_overrides,
            view.layout.typed_style_overrides
        );
        assert_eq!(view.layout.resolved_style().text_scale, 1.1);
        assert_eq!(view.layout.resolved_style().system_gap, 2.0);
    }

    #[test]
    fn score_style_defaults_are_inherited_then_overridden_by_view() {
        let mut score = Score::new("Style", 120, 4, 4, 0, 1);
        score.style_overrides = vec![
            ViewStyleOverride {
                property: ViewStyleProperty::StaffSpace,
                value: 1.2,
            },
            ViewStyleOverride {
                property: ViewStyleProperty::TextScale,
                value: 0.9,
            },
        ];
        let mut view = ScoreView::linked_part("part", "Part", 0);
        view.layout.typed_style_overrides.push(ViewStyleOverride {
            property: ViewStyleProperty::TextScale,
            value: 1.1,
        });
        let style = score.resolved_view_style(&view.layout);
        assert_eq!(style.staff_space, 1.2);
        assert_eq!(style.text_scale, 1.1);
        let restored: Score =
            serde_json::from_str(&serde_json::to_string(&score).unwrap()).unwrap();
        assert_eq!(restored.style_overrides, score.style_overrides);
    }

    #[test]
    fn legacy_measure_json_defaults_source_voice_numbers() {
        let score = Score::new("Legacy", 120, 4, 4, 0, 1);
        let mut value = serde_json::to_value(&score).expect("score serializes");
        value["parts"][0]["staves"][0]["measures"][0]
            .as_object_mut()
            .expect("measure is an object")
            .remove("source_voice_numbers");

        let restored: Score = serde_json::from_value(value).expect("legacy score deserializes");
        assert_eq!(
            restored.parts[0].staves[0].measures[0].source_voice_numbers,
            [None; 4]
        );
    }

    #[test]
    fn legacy_measure_json_defaults_tempo_ramp() {
        let measure: Measure = serde_json::from_str(
            r#"{"number":1,"time_sig":null,"key_sig":null,"clef":null,"tempo":120,"barline_left":"Normal","barline_right":"Normal","voices":[[],[],[],[]]}"#,
        )
        .expect("legacy measure deserializes");
        assert_eq!(measure.tempo_ramp_to, None);
    }

    #[test]
    fn note_without_new_percussion_fields_uses_serde_defaults() {
        let note = Note::new(Pitch::new(Step::C, 4), Duration::Quarter);
        let mut value = serde_json::to_value(note).unwrap();
        let object = value.as_object_mut().unwrap();
        object.remove("is_unpitched");
        object.remove("instrument_id");
        let restored: Note = serde_json::from_value(value).unwrap();
        assert!(!restored.is_unpitched);
        assert_eq!(restored.instrument_id, None);
    }

    #[test]
    fn percussion_instrument_resolution_prefers_id_then_display_key() {
        let mut part = Part::new("Drums", "Dr.");
        part.percussion_instruments = vec![
            PercussionInstrument {
                id: "snare".to_string(),
                name: Some("Acoustic Snare".to_string()),
                midi_unpitched: Some(38),
                staff_position: None,
                notehead: None,
                preferred_voice: None,
                techniques: Vec::new(),
            },
            PercussionInstrument {
                id: "rim".to_string(),
                name: Some("Side Stick".to_string()),
                midi_unpitched: Some(37),
                staff_position: None,
                notehead: None,
                preferred_voice: None,
                techniques: Vec::new(),
            },
        ];
        let mut note = Note::new(Pitch::from_midi(38, false), Duration::Quarter);
        note.is_unpitched = true;
        assert_eq!(
            part.percussion_instrument_for_note(&note)
                .map(|instrument| instrument.id.as_str()),
            Some("snare")
        );
        note.instrument_id = Some("rim".to_string());
        assert_eq!(
            part.percussion_instrument_for_note(&note)
                .map(|instrument| instrument.id.as_str()),
            Some("rim")
        );
        note.instrument_id = Some("missing".to_string());
        assert!(part.percussion_instrument_for_note(&note).is_none());
        note.instrument_id = None;
        note.is_unpitched = false;
        assert!(part.percussion_instrument_for_note(&note).is_none());
    }

    #[test]
    fn percussion_kit_extensions_are_json_backward_compatible() {
        let mut instrument = PercussionInstrument {
            id: "snare".to_string(),
            name: Some("Acoustic Snare".to_string()),
            midi_unpitched: Some(38),
            staff_position: Some(0),
            notehead: Some(NoteHead::Cross),
            preferred_voice: Some(1),
            techniques: vec!["rim-shot".to_string()],
        };
        let mut value = serde_json::to_value(&instrument).expect("instrument serializes");
        let object = value
            .as_object_mut()
            .expect("percussion instrument is an object");
        object.remove("staff_position");
        object.remove("notehead");
        object.remove("preferred_voice");
        object.remove("techniques");
        instrument = serde_json::from_value(value).expect("legacy instrument deserializes");
        assert_eq!(instrument.staff_position, None);
        assert_eq!(instrument.notehead, None);
        assert_eq!(instrument.preferred_voice, None);
        assert!(instrument.techniques.is_empty());
    }

    // ── ScoreTemplate ─────────────────────────────────────────────────────────

    #[test]
    fn score_template_solo_has_one_part_treble() {
        let score = Score::template(ScoreTemplate::Solo);
        assert_eq!(score.parts.len(), 1);
        assert_eq!(score.parts[0].staves.len(), 1);
        assert_eq!(score.parts[0].staves[0].clef, Clef::Treble);
        assert_eq!(score.parts[0].midi_program, 0);
    }

    #[test]
    fn score_template_piano_has_two_staves() {
        let score = Score::template(ScoreTemplate::Piano);
        assert_eq!(score.parts.len(), 1);
        assert_eq!(score.parts[0].staves.len(), 2);
        assert_eq!(score.parts[0].staves[0].clef, Clef::Treble);
        assert_eq!(score.parts[0].staves[1].clef, Clef::Bass);
    }

    #[test]
    fn score_template_string_quartet_has_four_parts() {
        let score = Score::template(ScoreTemplate::StringQuartet);
        assert_eq!(score.parts.len(), 4);
        assert_eq!(score.parts[2].staves[0].clef, Clef::Alto); // Viola
        assert_eq!(score.parts[3].staves[0].clef, Clef::Bass); // Cello
        assert_eq!(score.parts[0].midi_program, 40);
        assert_eq!(score.parts[3].midi_program, 42);
    }

    #[test]
    fn score_template_string_orchestra_has_five_parts() {
        let score = Score::template(ScoreTemplate::StringOrchestra);
        assert_eq!(score.parts.len(), 5);
        assert_eq!(score.parts[4].midi_program, 43); // Contrabass
    }

    #[test]
    fn score_template_brass_quintet_has_five_parts() {
        let score = Score::template(ScoreTemplate::BrassQuintet);
        assert_eq!(score.parts.len(), 5);
        assert_eq!(score.parts[2].midi_program, 60); // French Horn
    }

    #[test]
    fn score_template_default_measures_are_four() {
        let score = Score::template(ScoreTemplate::StringQuartet);
        for part in &score.parts {
            for staff in &part.staves {
                assert_eq!(staff.measures.len(), 4);
            }
        }
    }

    // ── system_break / page_break ─────────────────────────────────────────────

    #[test]
    fn measure_empty_has_no_breaks() {
        let m = Measure::empty(4, 4);
        assert!(!m.system_break);
        assert!(!m.page_break);
        assert!(!m.section_break);
    }

    #[test]
    fn section_range_uses_semantic_boundaries_not_layout_breaks() {
        let mut score = Score::new("sections", 120, 4, 4, 0, 6);
        score.parts[0].staves[0].measures[0].section_break = true;
        score.parts[0].staves[0].measures[2].section_break = true;
        score.parts[0].staves[0].measures[4].section_break = true;
        score.parts[0].staves[0].measures[5].section_break = true;
        score.parts[0].staves[0].measures[1].system_break = true;
        score.parts[0].staves[0].measures[3].page_break = true;
        assert_eq!(score.section_range(0).unwrap(), 0..=1);
        assert_eq!(score.section_range(3).unwrap(), 2..=3);
        assert_eq!(score.section_range(4).unwrap(), 4..=4);
        assert_eq!(score.section_range(5).unwrap(), 5..=5);
        assert!(score.section_range(6).is_err());
    }

    #[test]
    fn system_break_survives_json_roundtrip() {
        let mut m = Measure::empty(4, 4);
        m.system_break = true;
        let json = serde_json::to_string(&m).unwrap();
        let m2: Measure = serde_json::from_str(&json).unwrap();
        assert!(m2.system_break);
        assert!(!m2.page_break);
    }

    // ── diff ──────────────────────────────────────────────────────────────────

    #[test]
    fn diff_identical_scores_is_empty() {
        let s = Score::new("T", 120, 4, 4, 0, 2);
        assert!(diff(&s, &s).is_empty());
    }

    #[test]
    fn score_patch_covers_measure_semantics_and_note_insert_index() {
        let mut a = Score::new("T", 120, 4, 4, 0, 1);
        a.parts[0].staves[0].measures[0].voices[0].clear();
        let mut b = a.clone();
        let measure = &mut b.parts[0].staves[0].measures[0];
        measure.key_sig = Some(KeySignature {
            fifths: -2,
            mode: "major".to_string(),
        });
        measure.time_sig = Some(TimeSignature {
            numerator: 3,
            denominator: 4,
        });
        measure.barline_left = Barline::RepeatStart;
        measure.barline_right = Barline::RepeatEnd;
        measure.rehearsal = Some("A".to_string());
        measure.volta = Some(VoltaBracket {
            number: 1,
            kind: "begin_end".to_string(),
            numbers: Vec::new(),
        });
        measure.texts.push(StyledText {
            style: TextStyle::RehearsalMark,
            text: "A".to_string(),
            placement: None,
            offset_x: None,
            offset_y: None,
            relative_x: None,
            relative_y: None,
        });
        measure.figured_bass.push(FiguredBassFigure {
            number: "6".to_string(),
            alter: None,
            prefix: None,
            suffix: None,
            extender: false,
        });
        measure.harp_pedal_diagrams.push(HarpPedalDiagram {
            positions: [
                HarpPedalPosition::Flat,
                HarpPedalPosition::Natural,
                HarpPedalPosition::Sharp,
                HarpPedalPosition::Natural,
                HarpPedalPosition::Flat,
                HarpPedalPosition::Sharp,
                HarpPedalPosition::Natural,
            ],
            placement: Some("above".to_string()),
        });
        measure.voices[0].insert(0, Note::new(Pitch::new(Step::C, 4), Duration::Quarter));
        let expected = b.parts[0].staves[0].measures[0].clone();

        let patches = score_patch(&a, &b);
        assert!(
            patches
                .iter()
                .any(|p| matches!(p, ScorePatch::SetTimeSignature { .. }))
        );
        assert!(
            patches
                .iter()
                .any(|p| matches!(p, ScorePatch::SetBarlines { .. }))
        );
        assert!(
            patches
                .iter()
                .any(|p| matches!(p, ScorePatch::SetRehearsal { .. }))
        );
        assert!(
            patches
                .iter()
                .any(|p| matches!(p, ScorePatch::SetVolta { .. }))
        );
        assert!(
            patches
                .iter()
                .any(|p| matches!(p, ScorePatch::SetMeasureTexts { .. }))
        );
        assert!(
            patches
                .iter()
                .any(|p| matches!(p, ScorePatch::SetFiguredBass { .. }))
        );
        assert!(
            patches
                .iter()
                .any(|p| matches!(p, ScorePatch::SetHarpPedalDiagrams { .. }))
        );
        let result = apply_patch(&a, &patches).expect("patch application failed");
        let result_measure = &result.parts[0].staves[0].measures[0];
        assert_eq!(result_measure.key_sig, expected.key_sig);
        assert_eq!(result_measure.time_sig, expected.time_sig);
        assert_eq!(result_measure.barline_left, expected.barline_left);
        assert_eq!(result_measure.barline_right, expected.barline_right);
        assert_eq!(result_measure.rehearsal, expected.rehearsal);
        assert_eq!(result_measure.volta, expected.volta);
        assert_eq!(result_measure.texts, expected.texts);
        assert_eq!(result_measure.figured_bass, expected.figured_bass);
        assert_eq!(
            result_measure.harp_pedal_diagrams,
            expected.harp_pedal_diagrams
        );
        assert_eq!(result_measure.voices[0].len(), expected.voices[0].len());
    }

    #[test]
    fn diff_and_patch_preserve_score_level_texts() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.texts.push(StyledText {
            style: TextStyle::Expression,
            text: "Prelude".to_string(),
            placement: Some("above".to_string()),
            offset_x: Some(12.0),
            offset_y: Some(-8.0),
            relative_x: None,
            relative_y: None,
        });

        let changes = diff(&a, &b);
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::ScoreTextChanged { old, new }
                if old.is_empty() && new == &b.texts
        )));

        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetScoreTexts { value } if value == &b.texts
        )));
        let result = apply_patch(&a, &patches).expect("score text patch failed");
        assert_eq!(result.texts, b.texts);
    }

    #[test]
    fn measure_presentation_changes_use_typed_diff_and_local_patch() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        let measure = &mut b.parts[0].staves[0].measures[0];
        measure.number = 8;
        measure.clef = Some(Clef::Bass);
        measure.tempo_text = Some("Allegro".to_string());
        measure.navigation = Some("D.S.".to_string());
        measure.expression_text = Some("espressivo".to_string());
        measure.multi_rest_count = Some(3);
        measure.system_break = true;
        measure.page_break = true;

        let changes = diff(&a, &b);
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::MeasurePresentationChanged {
                part: 0,
                staff: 0,
                measure: 0,
                old_number: 1,
                new_number: 8,
                old_clef: None,
                new_clef: Some(Clef::Bass),
                new_tempo_text: Some(text),
                new_navigation: Some(navigation),
                new_expression_text: Some(expression),
                new_multi_rest_count: Some(3),
                old_system_break: false,
                new_system_break: true,
                old_page_break: false,
                new_page_break: true,
                ..
            } if text == "Allegro" && navigation == "D.S." && expression == "espressivo"
        )));
        assert!(!changes.iter().any(|change| matches!(
            change,
            ScoreChange::UnrepresentedFieldChanged { path }
                if path == "parts[0].staves[0].measures[0].number"
        )));

        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetMeasurePresentation {
                part: 0,
                staff: 0,
                measure: 0,
                number: 8,
                clef: Some(Clef::Bass),
                tempo_text: Some(text),
                navigation: Some(navigation),
                expression_text: Some(expression),
                multi_rest_count: Some(3),
                system_break: true,
                page_break: true,
                section_break: false,
            } if text == "Allegro" && navigation == "D.S." && expression == "espressivo"
        )));
        assert!(
            !patches
                .iter()
                .any(|patch| matches!(patch, ScorePatch::ReplaceScore { .. }))
        );
        let json = serde_json::to_string(&patches).expect("measure presentation patch JSON");
        let decoded: Vec<ScorePatch> =
            serde_json::from_str(&json).expect("measure presentation patch should decode");
        let mut legacy_json: serde_json::Value =
            serde_json::from_str(&json).expect("patch JSON value");
        for patch in legacy_json.as_array_mut().expect("patch JSON array") {
            patch
                .as_object_mut()
                .expect("patch JSON object")
                .remove("section_break");
        }
        let legacy: Vec<ScorePatch> =
            serde_json::from_value(legacy_json).expect("legacy patch should decode");
        assert!(matches!(
            legacy.first(),
            Some(ScorePatch::SetMeasurePresentation {
                section_break: false,
                ..
            })
        ));
        let result = apply_patch(&a, &decoded).expect("measure presentation patch failed");
        assert_eq!(result.parts[0].staves[0].measures[0].number, 8);
        assert_eq!(result.parts[0].staves[0].measures[0].clef, Some(Clef::Bass));
        assert_eq!(
            serde_json::to_value(&result).expect("patched score JSON"),
            serde_json::to_value(&b).expect("expected score JSON")
        );
    }

    #[test]
    fn chord_definition_changes_use_typed_diff_and_local_patch() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.chord_definitions.push(ChordDefinition {
            id: Some("c-major".to_string()),
            label: Some("C".to_string()),
            kind: Some("major".to_string()),
            fret_position: Some(0),
            tab_strings: Some("x32010".to_string()),
            tab_courses: None,
            members: Vec::new(),
            barres: Vec::new(),
        });

        let changes = diff(&a, &b);
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::ChordDefinitionsChanged { old, new }
                if old.is_empty() && new == &b.chord_definitions
        )));
        assert!(!changes.iter().any(|change| matches!(
            change,
            ScoreChange::UnrepresentedFieldChanged { path }
                if path == "chord_definitions"
        )));

        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetChordDefinitions { value } if value == &b.chord_definitions
        )));
        assert!(
            !patches
                .iter()
                .any(|patch| matches!(patch, ScorePatch::ReplaceScore { .. }))
        );
        let json = serde_json::to_string(&patches).expect("chord definition patch JSON");
        let decoded: Vec<ScorePatch> =
            serde_json::from_str(&json).expect("chord definition patch should decode");
        let result = apply_patch(&a, &decoded).expect("chord definition patch failed");
        assert_eq!(result.chord_definitions, b.chord_definitions);
    }

    #[test]
    fn part_name_changes_use_typed_diff_and_local_patch() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.parts[0].name = "Violin".to_string();
        b.parts[0].short_name = "Vln.".to_string();
        b.parts[0].midi_channel = 4;
        b.parts[0].midi_program = 40;
        b.parts[0].midi_pitch_bends.push(MidiPitchBend {
            tick: 120,
            channel: 4,
            value: 2048,
        });
        b.parts[0].midi_control_changes.push(MidiControlChange {
            tick: 240,
            channel: 4,
            controller: 64,
            value: 127,
        });
        b.parts[0].midi_program_changes.push(MidiProgramChange {
            tick: 0,
            channel: 4,
            program: 40,
        });
        b.parts[0].midi_aftertouch.push(MidiAftertouch {
            tick: 360,
            channel: 4,
            key: Some(64),
            value: 80,
        });
        b.parts[0].staves[0].clef = Clef::Bass;
        b.parts[0].staves[0].transpose_semitones = -2;

        let changes = diff(&a, &b);
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::PartNamesChanged {
                part: 0,
                old_name,
                new_name,
                old_short_name,
                new_short_name,
            } if old_name == "Piano"
                && new_name == "Violin"
                && old_short_name == "Pno."
                && new_short_name == "Vln."
        )));
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::PartMidiChanged {
                part: 0,
                old_channel: 0,
                new_channel: 4,
                old_program: 0,
                new_program: 40,
            }
        )));
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::PartMidiAutomationChanged {
                part: 0,
                new_pitch_bends,
                new_control_changes,
                new_program_changes,
                new_aftertouch,
                ..
            } if new_pitch_bends == &b.parts[0].midi_pitch_bends
                && new_control_changes == &b.parts[0].midi_control_changes
                && new_program_changes == &b.parts[0].midi_program_changes
                && new_aftertouch == &b.parts[0].midi_aftertouch
        )));
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::StaffConfigurationChanged {
                part: 0,
                staff: 0,
                old_clef: Clef::Treble,
                new_clef: Clef::Bass,
                old_transpose_semitones: 0,
                new_transpose_semitones: -2,
            }
        )));
        assert!(!changes.iter().any(|change| matches!(
            change,
            ScoreChange::UnrepresentedFieldChanged { path }
                if path == "parts[0].name"
        )));

        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetPartNames {
                part: 0,
                name,
                short_name,
            } if name == "Violin" && short_name == "Vln."
        )));
        assert!(
            !patches
                .iter()
                .any(|patch| matches!(patch, ScorePatch::ReplaceScore { .. }))
        );
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetPartMidi {
                part: 0,
                channel: 4,
                program: 40,
            }
        )));
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetPartMidiAutomation {
                part: 0,
                pitch_bends,
                control_changes,
                program_changes,
                aftertouch,
            } if pitch_bends == &b.parts[0].midi_pitch_bends
                && control_changes == &b.parts[0].midi_control_changes
                && program_changes == &b.parts[0].midi_program_changes
                && aftertouch == &b.parts[0].midi_aftertouch
        )));
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetStaffConfiguration {
                part: 0,
                staff: 0,
                clef: Clef::Bass,
                transpose_semitones: -2,
            }
        )));
        let result = apply_patch(&a, &patches).expect("part name patch failed");
        assert_eq!(result.parts[0].name, b.parts[0].name);
        assert_eq!(result.parts[0].short_name, b.parts[0].short_name);
        assert_eq!(result.parts[0].midi_channel, b.parts[0].midi_channel);
        assert_eq!(result.parts[0].midi_program, b.parts[0].midi_program);
        assert_eq!(
            result.parts[0].midi_pitch_bends,
            b.parts[0].midi_pitch_bends
        );
        assert_eq!(
            result.parts[0].midi_control_changes,
            b.parts[0].midi_control_changes
        );
        assert_eq!(
            result.parts[0].midi_program_changes,
            b.parts[0].midi_program_changes
        );
        assert_eq!(result.parts[0].midi_aftertouch, b.parts[0].midi_aftertouch);
        assert_eq!(result.parts[0].staves[0].clef, b.parts[0].staves[0].clef);
        assert_eq!(
            result.parts[0].staves[0].transpose_semitones,
            b.parts[0].staves[0].transpose_semitones
        );
    }

    #[test]
    fn diff_reports_measure_text_and_figured_bass_changes() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        let measure = &mut b.parts[0].staves[0].measures[0];
        measure.texts.push(StyledText {
            style: TextStyle::Lyrics,
            text: "la".to_string(),
            placement: None,
            offset_x: None,
            offset_y: None,
            relative_x: None,
            relative_y: None,
        });
        measure.figured_bass.push(FiguredBassFigure {
            number: "6".to_string(),
            alter: None,
            prefix: None,
            suffix: None,
            extender: false,
        });

        let changes = diff(&a, &b);
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::MeasureTextChanged { part: 0, staff: 0, measure: 0, old, new }
                if old.is_empty() && new.len() == 1
        )));
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::FiguredBassChanged { part: 0, staff: 0, measure: 0, old, new }
                if old.is_empty() && new.len() == 1
        )));
    }

    #[test]
    fn diff_reports_tablature_changes_and_patches_them_locally() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.parts[0].staves[0].tablature = Some(TablatureConfig {
            lines: 6,
            tuning_midi: vec![40, 45, 50, 55, 59, 64],
            capo: 2,
        });

        let changes = diff(&a, &b);
        assert!(!changes.iter().any(|change| matches!(
            change,
            ScoreChange::UnrepresentedFieldChanged { path }
                if path == "parts[0].staves[0].tablature"
        )));
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::TablatureConfigChanged { part: 0, staff: 0, old: None, new: Some(config) }
                if config.lines == 6 && config.capo == 2
        )));
        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetTablatureConfig { part: 0, staff: 0, value: Some(config) }
                if config.lines == 6 && config.capo == 2
        )));
        assert_eq!(
            apply_patch(&a, &patches).unwrap().parts[0].staves[0].tablature,
            b.parts[0].staves[0].tablature
        );
    }

    #[test]
    fn diff_reports_measure_tablature_changes_and_patches_them_locally() {
        let mut a = Score::new("T", 120, 4, 4, 0, 2);
        a.parts[0].staves[0].tablature = Some(TablatureConfig {
            lines: 6,
            tuning_midi: vec![40, 45, 50, 55, 59, 64],
            capo: 0,
        });
        let mut b = a.clone();
        b.parts[0].staves[0].measures[1].tablature_change = Some(TablatureConfig {
            lines: 6,
            tuning_midi: vec![40, 45, 50, 55, 59, 64],
            capo: 3,
        });

        let changes = diff(&a, &b);
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::TablatureChangeChanged {
                part: 0,
                staff: 0,
                measure: 1,
                old: None,
                new: Some(config),
            } if config.capo == 3
        )));
        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetMeasureTablatureChange {
                part: 0,
                staff: 0,
                measure: 1,
                value: Some(config),
            } if config.capo == 3
        )));
        assert_eq!(
            apply_patch(&a, &patches).unwrap().parts[0].staves[0].measures[1].tablature_change,
            b.parts[0].staves[0].measures[1].tablature_change
        );
    }

    #[test]
    fn diff_reports_measure_tempo_ramps_and_patches_them_locally() {
        let a = Score::new("Ramp", 120, 4, 4, 0, 2);
        let mut b = a.clone();
        b.parts[0].staves[0].measures[1].tempo_ramp_to = Some(72);

        assert!(diff(&a, &b).iter().any(|change| matches!(
            change,
            ScoreChange::MeasureTempoRampChanged {
                part: 0,
                staff: 0,
                measure: 1,
                old: None,
                new: Some(72),
            }
        )));
        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetMeasureTempoRamp {
                part: 0,
                staff: 0,
                measure: 1,
                value: Some(72),
            }
        )));
        assert_eq!(
            apply_patch(&a, &patches).expect("patch applies").parts[0].staves[0].measures[1]
                .tempo_ramp_to,
            b.parts[0].staves[0].measures[1].tempo_ramp_to
        );
    }

    #[test]
    fn diff_reports_staff_presentation_changes_and_patches_them_locally() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.parts[0].staves[0].presentation = StaffPresentation {
            kind: StaffKind::Percussion,
            lines: 1,
            line_distance: 1.5,
            small: true,
            cutaway: true,
            visible: false,
            notehead_scheme: StaffNoteheadScheme::PitchNames,
            tablature_rhythm_display: TablatureRhythmDisplay::FretOnly,
            tablature_fret_mark_style: TablatureFretMarkStyle::Arabic,
        };

        let changes = diff(&a, &b);
        assert!(changes.iter().any(|change| matches!(
            change,
            ScoreChange::StaffPresentationChanged { part: 0, staff: 0, new, .. }
                if new == &b.parts[0].staves[0].presentation
        )));
        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetStaffPresentation { part: 0, staff: 0, value }
                if value == &b.parts[0].staves[0].presentation
        )));
        assert!(
            !patches
                .iter()
                .any(|patch| matches!(patch, ScorePatch::ReplaceScore { .. }))
        );
        assert_eq!(
            apply_patch(&a, &patches).unwrap().parts[0].staves[0].presentation,
            b.parts[0].staves[0].presentation
        );
    }

    #[test]
    fn score_patch_uses_local_presentation_patch_for_display_fields() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.parts[0].name = "Piano".to_string();
        b.parts[0].staves[0].measures[0].expression_text = Some("dolce".to_string());
        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetMeasurePresentation {
                part: 0,
                staff: 0,
                measure: 0,
                expression_text: Some(text),
                ..
            } if text == "dolce"
        )));
        assert!(
            !patches
                .iter()
                .any(|patch| matches!(patch, ScorePatch::ReplaceScore { .. }))
        );
        let result = apply_patch(&a, &patches).expect("measure presentation patch failed");
        assert_eq!(result.parts[0].name, "Piano");
        assert_eq!(
            result.parts[0].staves[0].measures[0].expression_text,
            Some("dolce".to_string())
        );
    }

    #[test]
    fn diff_detects_tempo_change() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.settings.tempo_bpm = 90;
        let changes = diff(&a, &b);
        assert_eq!(changes.len(), 1);
        assert!(matches!(
            changes[0],
            ScoreChange::TempoChanged { old: 120, new: 90 }
        ));
    }

    #[test]
    fn diff_detects_title_change() {
        let a = Score::new("Old Title", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.metadata.title = "New Title".to_string();
        let changes = diff(&a, &b);
        assert!(
            changes.iter().any(
                |c| matches!(c, ScoreChange::MetadataChanged { field, .. } if field == "title")
            )
        );
    }

    #[test]
    fn diff_detects_note_modification() {
        let mut a = Score::new("T", 120, 4, 4, 0, 1);
        a.parts[0].staves[0].measures[0].voices[0] =
            vec![Note::new(Pitch::new(Step::C, 4), Duration::Quarter)];
        let mut b = a.clone();
        b.parts[0].staves[0].measures[0].voices[0][0] =
            Note::new(Pitch::new(Step::D, 4), Duration::Quarter);
        let changes = diff(&a, &b);
        assert!(
            changes
                .iter()
                .any(|c| matches!(c, ScoreChange::NoteModified { .. }))
        );
    }

    #[test]
    fn diff_detects_part_added() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        let mut p = Part::new("Violin", "Vln.");
        p.staves.push(Staff::new(Clef::Treble));
        b.parts.push(p);
        let changes = diff(&a, &b);
        assert!(
            changes
                .iter()
                .any(|c| matches!(c, ScoreChange::PartAdded { part_index: 1 }))
        );
    }

    #[test]
    fn diff_detects_measure_tempo_change() {
        let a = Score::new("T", 120, 4, 4, 0, 2);
        let mut b = a.clone();
        b.parts[0].staves[0].measures[1].tempo = Some(60);
        let changes = diff(&a, &b);
        assert!(changes.iter().any(|c| matches!(
            c,
            ScoreChange::MeasureTempoChanged {
                measure: 1,
                old: None,
                new: Some(60),
                ..
            }
        )));
    }

    #[test]
    fn diff_detects_barline_change() {
        use crate::model::notation::Barline;
        let a = Score::new("T", 120, 4, 4, 0, 2);
        let mut b = a.clone();
        b.parts[0].staves[0].measures[0].barline_left = Barline::RepeatStart;
        let changes = diff(&a, &b);
        assert!(
            changes
                .iter()
                .any(|c| matches!(c, ScoreChange::BarlineChanged { measure: 0, .. }))
        );
    }

    #[test]
    fn diff_detects_rehearsal_change() {
        let a = Score::new("T", 120, 4, 4, 0, 2);
        let mut b = a.clone();
        b.parts[0].staves[0].measures[0].rehearsal = Some("A".to_string());
        let changes = diff(&a, &b);
        assert!(
            changes
                .iter()
                .any(|c| matches!(c, ScoreChange::RehearsalMarkChanged { measure: 0, .. }))
        );
    }

    #[test]
    fn diff_detects_volta_change() {
        use super::VoltaBracket;
        let a = Score::new("T", 120, 4, 4, 0, 2);
        let mut b = a.clone();
        b.parts[0].staves[0].measures[0].volta = Some(VoltaBracket {
            number: 1,
            kind: "begin_end".into(),
            numbers: Vec::new(),
        });
        let changes = diff(&a, &b);
        assert!(
            changes
                .iter()
                .any(|c| matches!(c, ScoreChange::VoltaChanged { measure: 0, .. }))
        );
    }

    #[test]
    fn diff_detects_key_signature_change() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.settings.key_signature.fifths = 2; // C major → D major
        let changes = diff(&a, &b);
        assert!(
            changes
                .iter()
                .any(|c| matches!(c, ScoreChange::KeySignatureChanged { .. }))
        );
    }

    #[test]
    fn measure_key_signature_uses_typed_local_patch() {
        let a = Score::new("T", 120, 4, 4, 0, 1);
        let mut b = a.clone();
        b.parts[0].staves[0].measures[0].key_sig = Some(KeySignature {
            fifths: 2,
            mode: "major".to_string(),
        });
        let changes = diff(&a, &b);
        assert!(!changes.iter().any(|change| matches!(
            change,
            ScoreChange::UnrepresentedFieldChanged { path }
                if path == "parts[0].staves[0].measures[0].key_sig"
        )));
        let patches = score_patch(&a, &b);
        assert!(patches.iter().any(|patch| matches!(
            patch,
            ScorePatch::SetKeySignature {
                part: 0,
                staff: 0,
                measure: 0,
                value: Some(KeySignature { fifths: 2, .. }),
            }
        )));
        assert!(
            !patches
                .iter()
                .any(|patch| matches!(patch, ScorePatch::ReplaceScore { .. }))
        );
    }

    #[test]
    fn diff_same_key_signature_no_change() {
        let a = Score::new("T", 120, 4, 4, 2, 1);
        let changes = diff(&a, &a);
        assert!(changes.is_empty());
    }

    #[test]
    fn score_duration_secs_region_partial() {
        use super::score_duration_secs_region;
        // 4/4, 120 BPM, 4 measures → each measure = 2.0 s; region [1,2] = 4.0 s
        let score = Score::new("T", 120, 4, 4, 0, 4);
        let secs = score_duration_secs_region(&score, (1, 2));
        assert!((secs - 4.0).abs() < 0.01, "expected ~4.0 s, got {secs}");
    }

    #[test]
    fn score_duration_secs_region_single_measure() {
        use super::score_duration_secs_region;
        // 4/4, 120 BPM → 1 measure = 2.0 s
        let score = Score::new("T", 120, 4, 4, 0, 4);
        let secs = score_duration_secs_region(&score, (0, 0));
        assert!((secs - 2.0).abs() < 0.01, "expected ~2.0 s, got {secs}");
    }

    // ── measure_beats_remaining ───────────────────────────────────────────────

    #[test]
    fn measure_beats_remaining_empty_voice_returns_full() {
        use super::measure_beats_remaining;
        let mut score = Score::new("T", 120, 4, 4, 0, 1);
        score.parts[0].staves[0].measures[0].voices[0].clear();
        let rem = measure_beats_remaining(&score, 0, 0, 0, 0).unwrap();
        assert!(
            (rem - 4.0).abs() < 1e-9,
            "expected 4.0 remaining, got {rem}"
        );
    }

    #[test]
    fn measure_beats_remaining_half_full_returns_half() {
        use super::measure_beats_remaining;
        use crate::model::pitch::Step;
        let mut score = Score::new("T", 120, 4, 4, 0, 1);
        score.parts[0].staves[0].measures[0].voices[0] = vec![
            Note::new(Pitch::new(Step::C, 4), Duration::Quarter),
            Note::new(Pitch::new(Step::D, 4), Duration::Quarter),
        ];
        let rem = measure_beats_remaining(&score, 0, 0, 0, 0).unwrap();
        assert!(
            (rem - 2.0).abs() < 1e-9,
            "expected 2.0 remaining, got {rem}"
        );
    }

    #[test]
    fn measure_beats_remaining_full_voice_returns_zero() {
        use super::measure_beats_remaining;
        use crate::model::pitch::Step;
        let mut score = Score::new("T", 120, 4, 4, 0, 1);
        score.parts[0].staves[0].measures[0].voices[0] =
            vec![Note::new(Pitch::new(Step::C, 4), Duration::Whole)];
        let rem = measure_beats_remaining(&score, 0, 0, 0, 0).unwrap();
        assert!((rem).abs() < 1e-9, "expected 0.0 remaining, got {rem}");
    }

    #[test]
    fn measure_beats_remaining_tuplet_accounting() {
        use super::measure_beats_remaining;
        use crate::model::notation::TupletInfo;
        use crate::model::pitch::Step;
        // 3 quarter-note triplets each take 2/3 of a beat → total 2.0 beats used → 2.0 remaining
        let mut score = Score::new("T", 120, 4, 4, 0, 1);
        let tuplet = TupletInfo {
            actual_notes: 3,
            normal_notes: 2,
        };
        let mk = |step| {
            let mut n = Note::new(Pitch::new(step, 4), Duration::Quarter);
            n.tuplet = Some(tuplet.clone());
            n
        };
        score.parts[0].staves[0].measures[0].voices[0] =
            vec![mk(Step::C), mk(Step::D), mk(Step::E)];
        let rem = measure_beats_remaining(&score, 0, 0, 0, 0).unwrap();
        assert!(
            (rem - 2.0).abs() < 1e-9,
            "expected 2.0 remaining (triplets used 2.0), got {rem}"
        );
    }

    #[test]
    fn measure_beats_remaining_out_of_range_returns_err() {
        use super::measure_beats_remaining;
        let score = Score::new("T", 120, 4, 4, 0, 1);
        assert!(measure_beats_remaining(&score, 99, 0, 0, 0).is_err());
        assert!(measure_beats_remaining(&score, 0, 99, 0, 0).is_err());
        assert!(measure_beats_remaining(&score, 0, 0, 99, 0).is_err());
        assert!(measure_beats_remaining(&score, 0, 0, 0, 4).is_err());
    }

    #[test]
    fn note_content_eq_ignores_id() {
        use crate::model::pitch::Step;
        let mut a = Note::new(Pitch::new(Step::C, 4), Duration::Quarter);
        let mut b = a.clone();
        b.id = "different-id".to_string();
        assert!(note_content_eq(&a, &b));
        // Actual pitch change should differ
        b.pitches[0] = Pitch::new(Step::D, 4);
        assert!(!note_content_eq(&a, &b));
        // stem_up difference
        let mut c = a.clone();
        a.stem_up = Some(true);
        c.stem_up = Some(false);
        assert!(!note_content_eq(&a, &c));
    }

    #[test]
    fn suggested_stem_up_below_middle() {
        use crate::model::notation::Clef;
        // C4 = MIDI 60, Treble middle = B4 = 71 → stem up
        let pitches = vec![Pitch::new(Step::C, 4)];
        assert!(suggested_stem_up(&pitches, &Clef::Treble));
    }

    #[test]
    fn suggested_stem_up_above_middle() {
        use crate::model::notation::Clef;
        // G5 = MIDI 79, Treble middle = 71 → stem down
        let pitches = vec![Pitch::new(Step::G, 5)];
        assert!(!suggested_stem_up(&pitches, &Clef::Treble));
    }

    #[test]
    fn suggested_stem_up_at_middle_line() {
        use crate::model::notation::Clef;
        // B4 = MIDI 71, Treble middle = 71 → stem down (avg >= middle)
        let pitches = vec![Pitch::new(Step::B, 4)];
        assert!(!suggested_stem_up(&pitches, &Clef::Treble));
    }

    #[test]
    fn suggested_stem_up_chord() {
        use crate::model::notation::Clef;
        // [C4=60, G4=67] avg=63.5 < 71 → stem up
        let pitches = vec![Pitch::new(Step::C, 4), Pitch::new(Step::G, 4)];
        assert!(suggested_stem_up(&pitches, &Clef::Treble));
    }

    #[test]
    fn suggested_stem_up_bass_clef() {
        use crate::model::notation::Clef;
        // D3=50 is exactly at Bass middle line → stem down
        let pitches = vec![Pitch::new(Step::D, 3)];
        assert!(!suggested_stem_up(&pitches, &Clef::Bass));
        // C3=48 < 50 → stem up
        let pitches2 = vec![Pitch::new(Step::C, 3)];
        assert!(suggested_stem_up(&pitches2, &Clef::Bass));
    }

    #[test]
    fn suggested_stem_up_empty_pitches() {
        use crate::model::notation::Clef;
        assert!(suggested_stem_up(&[], &Clef::Treble));
    }

    fn eighth(pitch: Pitch) -> Note {
        Note::new(pitch, Duration::Eighth)
    }
    fn quarter(pitch: Pitch) -> Note {
        Note::new(pitch, Duration::Quarter)
    }
    fn rest_eighth() -> Note {
        Note::rest(Duration::Eighth)
    }

    #[test]
    fn compute_beams_4_4_four_eighths() {
        use crate::model::notation::{Clef, TimeSignature};
        let _ = Clef::Treble; // suppress unused import warning
        let ts = TimeSignature {
            numerator: 4,
            denominator: 4,
        };
        let c4 = Pitch::new(Step::C, 4);
        let notes = vec![
            eighth(c4.clone()),
            eighth(c4.clone()),
            eighth(c4.clone()),
            eighth(c4.clone()),
        ];
        let beams = compute_beams(&notes, &ts);
        // 4 eighths in 4/4: beat size=1.0, two groups of 2 each
        assert_eq!(beams[0], BeamState::Begin);
        assert_eq!(beams[1], BeamState::End);
        assert_eq!(beams[2], BeamState::Begin);
        assert_eq!(beams[3], BeamState::End);
    }

    #[test]
    fn compute_beams_4_4_all_eighth_one_group() {
        use crate::model::notation::TimeSignature;
        let ts = TimeSignature {
            numerator: 4,
            denominator: 4,
        };
        let c4 = Pitch::new(Step::C, 4);
        // 2 eighths in a beat → group of 2
        let notes = vec![eighth(c4.clone()), eighth(c4.clone())];
        let beams = compute_beams(&notes, &ts);
        assert_eq!(beams[0], BeamState::Begin);
        assert_eq!(beams[1], BeamState::End);
    }

    #[test]
    fn compute_beams_quarter_not_beamed() {
        use crate::model::notation::TimeSignature;
        let ts = TimeSignature {
            numerator: 4,
            denominator: 4,
        };
        let c4 = Pitch::new(Step::C, 4);
        let notes = vec![quarter(c4.clone()), quarter(c4.clone())];
        let beams = compute_beams(&notes, &ts);
        assert_eq!(beams[0], BeamState::None);
        assert_eq!(beams[1], BeamState::None);
    }

    #[test]
    fn compute_beams_rest_breaks_beam() {
        use crate::model::notation::TimeSignature;
        let ts = TimeSignature {
            numerator: 4,
            denominator: 4,
        };
        let c4 = Pitch::new(Step::C, 4);
        let notes = vec![eighth(c4.clone()), rest_eighth(), eighth(c4.clone())];
        let beams = compute_beams(&notes, &ts);
        // rest breaks beam group
        assert_eq!(beams[0], BeamState::None);
        assert_eq!(beams[1], BeamState::None);
        assert_eq!(beams[2], BeamState::None);
    }

    #[test]
    fn compute_beams_6_8_compound() {
        use crate::model::notation::TimeSignature;
        let ts = TimeSignature {
            numerator: 6,
            denominator: 8,
        };
        let c4 = Pitch::new(Step::C, 4);
        // 6 eighths in 6/8 compound → two groups of 3 (beam size=1.5 beats)
        let notes: Vec<Note> = (0..6).map(|_| eighth(c4.clone())).collect();
        let beams = compute_beams(&notes, &ts);
        assert_eq!(beams[0], BeamState::Begin);
        assert_eq!(beams[1], BeamState::Continue);
        assert_eq!(beams[2], BeamState::End);
        assert_eq!(beams[3], BeamState::Begin);
        assert_eq!(beams[4], BeamState::Continue);
        assert_eq!(beams[5], BeamState::End);
    }

    #[test]
    fn compute_beams_single_eighth() {
        use crate::model::notation::TimeSignature;
        let ts = TimeSignature {
            numerator: 4,
            denominator: 4,
        };
        let c4 = Pitch::new(Step::C, 4);
        let notes = vec![eighth(c4.clone())];
        let beams = compute_beams(&notes, &ts);
        assert_eq!(beams[0], BeamState::None);
    }

    #[test]
    fn compute_beams_stops_fifteen_in_eight_tuplet_at_the_beat_boundary() {
        let ts = TimeSignature {
            numerator: 2,
            denominator: 4,
        };
        let pitch = Pitch::new(Step::C, 4);
        let mut tuplet_note = Note::new(pitch.clone(), Duration::ThirtySecond);
        tuplet_note.tuplet = Some(TupletInfo {
            actual_notes: 15,
            normal_notes: 8,
        });
        let mut notes = vec![tuplet_note; 15];
        notes.extend([eighth(pitch.clone()), eighth(pitch)]);
        let original = serde_json::to_value(&notes).unwrap();

        let beams = compute_beams(&notes, &ts);
        let mut expected = vec![BeamState::Begin];
        expected.extend([BeamState::Continue; 13]);
        expected.extend([BeamState::End, BeamState::Begin, BeamState::End]);
        assert_eq!(beams, expected);
        assert_eq!(
            serde_json::to_value(&notes).unwrap(),
            original,
            "beam inference must not change notation or timing"
        );
        assert!((notes[..15].iter().map(Note::beats).sum::<f64>() - 1.0).abs() < 1e-12);
    }
}

#[cfg(test)]
mod mid_clef_tests {
    use super::*;
    use crate::{Command, JoinMeasuresCmd, ScoreEngine, SetMidMeasureClefsCmd, SplitMeasureCmd};

    fn quarter_notes() -> Vec<Note> {
        [Step::C, Step::D, Step::E, Step::F]
            .into_iter()
            .map(|step| Note::new(Pitch::new(step, 4), Duration::Quarter))
            .collect()
    }

    fn change(beats: f64, clef: Clef) -> MidMeasureClef {
        MidMeasureClef {
            offset: MeasureLength::from_beats(beats).unwrap(),
            clef,
        }
    }

    #[test]
    fn measure_length_from_beats_is_exact_for_tuplet_subdivisions() {
        let third = MeasureLength::from_beats(1.0 / 3.0).unwrap();
        assert_eq!((third.numerator, third.denominator), (1, 12));
        let two = MeasureLength::from_beats(2.0).unwrap();
        assert_eq!((two.numerator, two.denominator), (1, 2));
        assert!(MeasureLength::from_beats(0.0).is_none());
    }

    #[test]
    fn clef_at_follows_mid_bar_changes_and_json_omits_an_empty_list() {
        let mut measure = Measure::empty(4, 4);
        let json = serde_json::to_string(&measure).unwrap();
        assert!(!json.contains("mid_clefs"));
        measure.mid_clefs = vec![change(2.0, Clef::Bass)];
        assert_eq!(measure.clef_at(&Clef::Treble, 1.0), Clef::Treble);
        assert_eq!(measure.clef_at(&Clef::Treble, 2.0), Clef::Bass);
        let restored: Measure =
            serde_json::from_str(&serde_json::to_string(&measure).unwrap()).unwrap();
        assert_eq!(restored.mid_clefs, measure.mid_clefs);
    }

    #[test]
    fn validation_rejects_mid_bar_clefs_outside_the_bar_or_out_of_order() {
        let mut score = Score::new("clefs", 120, 4, 4, 0, 1);
        score.parts[0].staves[0].measures[0].voices[0] = quarter_notes();
        score.parts[0].staves[0].measures[0].mid_clefs =
            vec![change(2.0, Clef::Bass), change(1.0, Clef::Treble)];
        let errors = crate::validate(&score).errors;
        assert!(errors.iter().any(|error| matches!(
            error,
            crate::ValidationError::InvalidMidMeasureClef { index: 1, .. }
        )));
        score.parts[0].staves[0].measures[0].mid_clefs = vec![change(4.0, Clef::Bass)];
        assert!(!crate::validate(&score).errors.is_empty());
    }

    #[test]
    fn command_split_join_diff_and_patch_keep_mid_bar_clefs() {
        let mut engine = ScoreEngine::new();
        engine.score.parts[0].staves[0].measures[0].voices[0] = quarter_notes();
        engine
            .apply(Command::SetMidMeasureClefs(SetMidMeasureClefsCmd {
                part_index: 0,
                staff_index: 0,
                measure_index: 0,
                clefs: vec![change(1.0, Clef::Bass), change(3.0, Clef::Alto)],
            }))
            .unwrap();
        let with_clefs = engine.score.clone();
        let plain = {
            let mut score = with_clefs.clone();
            score.parts[0].staves[0].measures[0].mid_clefs.clear();
            score
        };
        assert!(diff(&plain, &with_clefs).iter().any(|change| matches!(
            change,
            ScoreChange::MidMeasureClefsChanged { measure: 0, .. }
        )));
        let patched = apply_patch(&plain, &score_patch(&plain, &with_clefs)).unwrap();
        assert_eq!(
            patched.parts[0].staves[0].measures[0].mid_clefs,
            with_clefs.parts[0].staves[0].measures[0].mid_clefs
        );

        engine
            .apply(Command::SplitMeasure(SplitMeasureCmd {
                measure_index: 0,
                split_at_beats: 1.0,
            }))
            .unwrap();
        let measures = &engine.score.parts[0].staves[0].measures;
        assert!(measures[0].mid_clefs.is_empty());
        assert_eq!(measures[1].clef, Some(Clef::Bass));
        assert_eq!(measures[1].mid_clefs, vec![change(2.0, Clef::Alto)]);

        engine
            .apply(Command::JoinMeasures(JoinMeasuresCmd { measure_index: 0 }))
            .unwrap();
        let measure = &engine.score.parts[0].staves[0].measures[0];
        assert_eq!(
            measure.mid_clefs,
            vec![change(1.0, Clef::Bass), change(3.0, Clef::Alto)]
        );

        let invalid = engine.apply(Command::SetMidMeasureClefs(SetMidMeasureClefsCmd {
            part_index: 0,
            staff_index: 0,
            measure_index: 0,
            clefs: vec![change(0.0 + 5.0, Clef::Bass)],
        }));
        assert!(invalid.is_err());
    }
}

#[cfg(test)]
mod percussion_key_tests {
    use super::*;

    #[test]
    fn unpitched_chord_members_sound_their_kit_keys_by_display_position() {
        let mut part = Part::new("Drums", "Dr.");
        part.midi_channel = 9;
        let kit = |id: &str, key: u8, display: Pitch| PercussionInstrument {
            id: id.into(),
            name: None,
            midi_unpitched: Some(key),
            staff_position: Some(PercussionInstrument::display_position(&display)),
            notehead: None,
            preferred_voice: None,
            techniques: Vec::new(),
        };
        part.percussion_instruments = vec![
            kit("kick", 35, Pitch::new(Step::F, 4)),
            kit("snare", 38, Pitch::new(Step::C, 5)),
        ];
        let mut note = Note::new(Pitch::new(Step::C, 5), Duration::Quarter);
        note.pitches.push(Pitch::new(Step::F, 4));
        note.is_unpitched = true;
        note.instrument_id = Some("snare".into());
        assert_eq!(part.percussion_key(&note, 0), Some(38));
        assert_eq!(part.percussion_key(&note, 1), Some(35));
        note.is_unpitched = false;
        assert_eq!(part.percussion_key(&note, 0), None);
        assert_eq!(
            PercussionInstrument::display_position(&Pitch::new(Step::B, 4)),
            0
        );
    }
}