nooise 2.5.3

//! The Tonal voice: melodic steps over a pentatonic scale, with an
//! evolving phrase and per-step randomness.

use super::*;

pub(crate) struct TonalEngine {
    pub(crate) sample_rate: f32,
    pub(crate) step_trigger: GridTrigger,
    pub(crate) step_index: usize,
    pub(crate) active_phrase: usize,
    pub(crate) last_cycle: Option<u64>,
    pub(crate) evolved_phrase: Vec<i32>,
    pub(crate) voices: Vec<TonalVoice>,
    pub(crate) low_cut_l: TonalLowCut,
    pub(crate) low_cut_r: TonalLowCut,
    pub(crate) rng: StdRng,
    evolution_seed: u64,
    evolution_count: u64,
    session_state: Option<LiveSession>,
}

/// The mutable melodic state a song snapshot needs to resume evolution.
/// Playback RNG stays separate because it only affects incidental random notes
/// and panning, not which future evolution mutation occurs.
#[derive(Clone, Debug, PartialEq, Eq)]
pub(crate) struct TonalSequenceState {
    pub(crate) phrase: usize,
    pub(crate) notes: Vec<i32>,
    pub(crate) evolution_seed: u64,
    pub(crate) evolution_count: u64,
}

impl TonalSequenceState {
    pub(crate) fn from_phrase(phrase: usize) -> Self {
        let phrase = phrase % TONAL_PHRASES.len();
        Self {
            phrase,
            notes: tonal_phrase(phrase).to_vec(),
            evolution_seed: rand::random(),
            evolution_count: 0,
        }
    }
}

pub(crate) const TONAL_LOW_CUT_HZ: f32 = 70.0;
/// Floor for the shared `decay` control (seconds). Held above zero so the amp
/// envelope always has a real fade to silence — a literal 0 would cut the note
/// at full amplitude in a single sample and click. Shared by tonal and arp.
pub(crate) const TONAL_DECAY_MIN: f32 = 0.01;
pub(crate) const TONAL_RATE_BEATS_MIN: f32 = 0.125;
pub(crate) const TONAL_RATE_BEATS_MAX: f32 = 4.0;
pub(crate) const TONAL_CYCLE_BEATS_MIN: f32 = TONAL_RATE_BEATS_MIN;
pub(crate) const TONAL_CYCLE_BEATS_MAX: f32 = 16.0;
pub(crate) const TONAL_MAX_LOOP_STEPS: usize = 64;
pub(crate) const TONAL_MAX_EVOLVE_NOTES: usize = 4;
pub(crate) const TONAL_SCALE_MIDI: [i32; 10] = [45, 48, 50, 52, 55, 57, 60, 62, 64, 67];
pub(crate) const TONAL_PIANO_HARMONIC_COUNT: usize = 16;
pub(crate) const TONAL_PIANO_PROFILE_COUNT: usize = 9;
pub(crate) const TONAL_PIANO_A_KEYFRAMES: [PianoKeyframe; 3] = [
    PianoKeyframe {
        midi: 36,
        decay_factor: 3.0,
        harmonics: [
            0.03703704, 0.07407408, 0.22222224, 0.15308644, 0.18024692, 0.21481483, 0.24691358,
            0.04938272, 0.03703704, 0.05679013, 0.11111112, 0.05432099, 0.22716051, 0.04938272,
            0.04938272, 0.03703704,
        ],
    },
    PianoKeyframe {
        midi: 48,
        decay_factor: 2.0,
        harmonics: [
            0.04368932,
            0.43689322,
            0.18786408,
            0.04368932,
            0.1485437,
            0.10048544,
            0.30582526,
            0.034951456,
            0.052427184,
            0.10048544,
            0.04805825,
            0.07427185,
            0.026213592,
            0.10048544,
            0.078640774,
            0.017475728,
        ],
    },
    PianoKeyframe {
        midi: 60,
        decay_factor: 1.0,
        harmonics: [
            0.57937425,
            0.17381229,
            0.06546929,
            0.052143686,
            0.024913093,
            0.052143686,
            0.035921205,
            0.0063731167,
            0.004634994,
            0.0011587485,
            0.0011587485,
            0.0011587485,
            0.00057937426,
            0.00028968713,
            0.00057937426,
            0.00028968713,
        ],
    },
];
pub(crate) const TONAL_MARIMBA_KEYFRAMES: [PianoKeyframe; 4] = [
    PianoKeyframe {
        midi: 36,
        decay_factor: 3.0,
        harmonics: [
            0.6043514,
            0.009669623,
            0.009669623,
            0.030217571,
            0.024174057,
            0.030217571,
            0.018130543,
            0.018130543,
            0.030217571,
            0.25987113,
            0.060435142,
            0.24174057,
            0.060435142,
            0.042304598,
            0.030217571,
            0.030217571,
        ],
    },
    PianoKeyframe {
        midi: 48,
        decay_factor: 2.0,
        harmonics: [
            0.38923132,
            0.011676939,
            0.038923133,
            0.17126179,
            0.02919235,
            0.015569253,
            0.011676939,
            0.0077846264,
            0.038923133,
            0.32695428,
            0.108984776,
            0.019461567,
            0.023353878,
            0.0031138507,
            0.002335388,
            0.0015569254,
        ],
    },
    PianoKeyframe {
        midi: 60,
        decay_factor: 1.0,
        harmonics: [
            0.6660065,
            0.0048003546,
            0.013320129,
            0.17499822,
            0.0066600647,
            0.0,
            0.002664026,
            0.00020980158,
            0.0005268287,
            0.13081412,
            0.0,
            0.0,
            0.0,
            0.0,
            0.0,
            0.0,
        ],
    },
    PianoKeyframe {
        midi: 84,
        decay_factor: 1.0,
        harmonics: [
            0.77432626,
            0.0034792372,
            0.00040290528,
            0.0,
            0.018717118,
            0.0030744278,
            0.0,
            0.0,
            0.0,
            0.0,
            0.0,
            0.0,
            0.0,
            0.0,
            0.0,
            0.0,
        ],
    },
];
// Electric-piano spectrum: fundamental-dominant with a soft "tine" bump
// around the 5th/6th partial and a fast upper rolloff. Warm, non-metallic —
// the reeds fade quickly so nothing rings out bright.
pub(crate) const TONAL_EP_KEYFRAMES: [PianoKeyframe; 3] = [
    PianoKeyframe {
        midi: 36,
        decay_factor: 2.6,
        harmonics: [
            0.6, 0.168, 0.072, 0.036, 0.084, 0.06, 0.024, 0.012, 0.009, 0.006, 0.0048, 0.003,
            0.0024, 0.0018, 0.0012, 0.0006,
        ],
    },
    PianoKeyframe {
        midi: 48,
        decay_factor: 1.8,
        harmonics: [
            0.6, 0.132, 0.054, 0.03, 0.06, 0.036, 0.018, 0.009, 0.006, 0.0036, 0.0024, 0.0018,
            0.0012, 0.0009, 0.0006, 0.00048,
        ],
    },
    PianoKeyframe {
        midi: 60,
        decay_factor: 1.0,
        harmonics: [
            0.6, 0.09, 0.036, 0.018, 0.03, 0.018, 0.009, 0.0048, 0.003, 0.0018, 0.0012, 0.0006,
            0.00048, 0.0003, 0.00024, 0.00018,
        ],
    },
];
// Types 1-9 (profile index = type - 1). Type 8 / profile[7] is Cloud Keys,
// the keeper, left exactly as tuned. The rest are warm, non-metallic keys
// voiced for ambient techno: soft attacks, unhurried decays, gentle tops.
pub(crate) const TONAL_PIANO_PROFILES: [PianoProfile; TONAL_PIANO_PROFILE_COUNT] = [
    // Rhodes: warm electric piano, quick bell-tine attack, mellow sustain.
    PianoProfile {
        keyframes: &TONAL_EP_KEYFRAMES,
        amplitude: 0.40,
        body_power: 0.35,
        harmonic_tilt: -0.70,
        decay_low: 0.70,
        decay_high: 4.2,
        decay_scale: 0.60,
    },
    // Wurli: reedier electric piano, a touch more bark and shorter tail.
    PianoProfile {
        keyframes: &TONAL_EP_KEYFRAMES,
        amplitude: 0.44,
        body_power: 0.45,
        harmonic_tilt: -0.85,
        decay_low: 0.50,
        decay_high: 3.6,
        decay_scale: 0.50,
    },
    // Felt: muted upright with the soft attack of a felt-covered hammer.
    PianoProfile {
        keyframes: &TONAL_PIANO_A_KEYFRAMES,
        amplitude: 0.36,
        body_power: 0.30,
        harmonic_tilt: -1.05,
        decay_low: 0.45,
        decay_high: 3.4,
        decay_scale: 0.50,
    },
    // Marimba: wooden mallet, percussive body, rounded overtones.
    PianoProfile {
        keyframes: &TONAL_MARIMBA_KEYFRAMES,
        amplitude: 0.30,
        body_power: 0.78,
        harmonic_tilt: -0.95,
        decay_low: 1.0,
        decay_high: 5.8,
        decay_scale: 0.62,
    },
    // Kalimba: plucked lamellophone, fundamental-heavy, gentle ring.
    PianoProfile {
        keyframes: &TONAL_EP_KEYFRAMES,
        amplitude: 0.34,
        body_power: 0.70,
        harmonic_tilt: -0.60,
        decay_low: 1.1,
        decay_high: 6.5,
        decay_scale: 0.50,
    },
    // Pluck: short, dry, staccato key stab for rhythmic ambient patterns.
    PianoProfile {
        keyframes: &TONAL_EP_KEYFRAMES,
        amplitude: 0.36,
        body_power: 0.85,
        harmonic_tilt: -0.70,
        decay_low: 1.2,
        decay_high: 6.0,
        decay_scale: 0.45,
    },
    // Dulcet: clear, sweet upright with a little more shimmer than Felt.
    PianoProfile {
        keyframes: &TONAL_PIANO_A_KEYFRAMES,
        amplitude: 0.38,
        body_power: 0.40,
        harmonic_tilt: -0.70,
        decay_low: 0.70,
        decay_high: 5.0,
        decay_scale: 0.68,
    },
    // Cloud Keys: the keeper. Airy, dark, slow-blooming pad piano.
    PianoProfile {
        keyframes: &TONAL_PIANO_A_KEYFRAMES,
        amplitude: 0.34,
        body_power: 0.18,
        harmonic_tilt: -1.20,
        decay_low: 0.28,
        decay_high: 2.4,
        decay_scale: 0.34,
    },
    // Haze: an even softer, slower sibling of Cloud — a breath of a key.
    PianoProfile {
        keyframes: &TONAL_PIANO_A_KEYFRAMES,
        amplitude: 0.32,
        body_power: 0.16,
        harmonic_tilt: -1.15,
        decay_low: 0.30,
        decay_high: 2.8,
        decay_scale: 0.38,
    },
];
pub(crate) const TONAL_PHRASES: [&[i32]; 8] = [
    &[45, 50, 55, 48, 52, 57, 50, 55],
    &[45, 52, 57, 60, 57, 52, 50, 48, 50, 55, 52, 45],
    &[57, 60, 64, 62, 60, 57, 52, 55],
    &[45, 48, 52, 55, 60, 57, 55, 52, 50, 52, 55, 48],
    &[52, 55, 60, 64, 67, 64, 60, 55],
    &[
        45, 50, 52, 55, 57, 55, 52, 50, 48, 50, 52, 45, 43, 45, 48, 50,
    ],
    &[60, 57, 55, 52, 50, 52, 55, 57],
    &[
        45, 48, 50, 55, 52, 57, 55, 60, 57, 64, 60, 67, 64, 60, 55, 52,
    ],
];

impl TonalEngine {
    #[cfg(test)]
    pub(crate) fn new(sample_rate: f32) -> Self {
        Self::new_with_session_state(sample_rate, None)
    }

    pub(crate) fn new_with_session_state(
        sample_rate: f32,
        session_state: Option<LiveSession>,
    ) -> Self {
        let state = session_state
            .as_ref()
            .map(|state| state.load().tonal_sequence.clone())
            .unwrap_or_else(|| TonalSequenceState::from_phrase(0));
        Self {
            sample_rate,
            step_trigger: GridTrigger::new(),
            step_index: 0,
            active_phrase: state.phrase,
            last_cycle: None,
            evolved_phrase: state.notes,
            voices: Vec::with_capacity(8),
            low_cut_l: TonalLowCut::new(sample_rate, TONAL_LOW_CUT_HZ),
            low_cut_r: TonalLowCut::new(sample_rate, TONAL_LOW_CUT_HZ),
            rng: StdRng::from_entropy(),
            evolution_seed: state.evolution_seed,
            evolution_count: state.evolution_count,
            session_state,
        }
    }

    pub(crate) fn next(
        &mut self,
        c: &TonalControls,
        tune: f32,
        timing: TimingContext,
    ) -> (f32, f32) {
        let phrase = wrapped_index(c.phrase, TONAL_PHRASES.len());
        self.sync_phrase(phrase);

        if self
            .step_trigger
            .pop_swung(timing, c.rate_beats, 0.0, c.swing)
        {
            let cycle = tonal_cycle_index(timing.beat, c.step_interval_beats);
            if self.last_cycle.is_some_and(|last| last != cycle) {
                self.evolve_phrase(c.evolve_rate);
            }
            self.last_cycle = Some(cycle);

            let loop_len = tonal_loop_len(c.step_interval_beats, c.rate_beats);
            self.step_index = tonal_cycle_step(timing.beat, c.step_interval_beats, c.rate_beats)
                % loop_len
                + tonal_offset_step(c.offset_beats, c.rate_beats);
            let note = if self.rng.gen_range(0.0f32..1.0) < c.randomness {
                TONAL_SCALE_MIDI[self.rng.gen_range(0..TONAL_SCALE_MIDI.len())]
            } else {
                self.evolved_phrase[self.step_index % self.evolved_phrase.len()]
            } + (c.octave.round() as i32) * 12;
            let hz = note_hz(note, tune);
            let pan = self.rng.gen_range(-0.5f32..0.5);
            // A silent layer still triggers nothing: skipping keeps a Level
            // of exactly 0 from accumulating inaudible voices. Every RNG draw
            // above still happens, keeping seeded renders byte-identical.
            if c.level != 0.0 {
                self.voices.push(TonalVoice::new(
                    wrapped_index(c.synth_type, TONAL_SYNTH_TYPES.len()),
                    TonalNote {
                        midi: note,
                        hz,
                        pan,
                        sample_rate: self.sample_rate,
                        attack_time: c.attack,
                        decay_time: c.decay,
                    },
                ));
            }
        }

        let (dry_l, dry_r) =
            mix_and_retain(&mut self.voices, TonalVoice::next, TonalVoice::is_done);

        // Level is applied here, to the summed voices, rather than captured
        // into each note at trigger time: a note that has already started
        // must still answer the fader. `c.level` arrives pre-smoothed from
        // `GainSmoothers`, so this stays click-free.
        //
        // It scales the low cut's *output*, never its input. The cut is a
        // high pass, so feeding it an abruptly silenced signal discharges its
        // state as a decaying thump — the filter must keep seeing the voices
        // at full level and never learn that the fader moved.
        (
            self.low_cut_l.process(dry_l) * c.level,
            self.low_cut_r.process(dry_r) * c.level,
        )
    }

    pub(crate) fn sync_phrase(&mut self, phrase: usize) {
        if phrase != self.active_phrase {
            self.active_phrase = phrase;
            self.evolved_phrase = tonal_phrase(phrase).to_vec();
            self.step_index = 0;
            self.last_cycle = None;
            self.evolution_seed = rand::random();
            self.evolution_count = 0;
            self.publish_session_state();
        }
    }

    pub(crate) fn evolve_phrase(&mut self, rate: f32) {
        let count = tonal_evolve_note_count(rate, self.evolved_phrase.len());
        if count == 0 {
            return;
        }
        let mut changed_positions = [usize::MAX; TONAL_MAX_EVOLVE_NOTES];
        for changed in 0..count {
            let mut pos = evolve_random(self.evolution_seed, self.evolution_count, changed as u64)
                as usize
                % self.evolved_phrase.len();
            while changed_positions[..changed].contains(&pos) {
                pos = (pos + 1) % self.evolved_phrase.len();
            }
            changed_positions[changed] = pos;

            let old = self.evolved_phrase[pos];
            let mut next = old;
            for attempt in 0..8 {
                next = TONAL_SCALE_MIDI[evolve_random(
                    self.evolution_seed,
                    self.evolution_count,
                    TONAL_MAX_EVOLVE_NOTES as u64 + changed as u64 * 8 + attempt,
                ) as usize
                    % TONAL_SCALE_MIDI.len()];
                if next != old {
                    break;
                }
            }
            self.evolved_phrase[pos] = next;
        }
        self.evolution_count = self.evolution_count.wrapping_add(1);
        self.publish_session_state();
    }

    fn publish_session_state(&self) {
        let Some(session_state) = &self.session_state else {
            return;
        };
        session_state.update(|snapshot| {
            snapshot.tonal_sequence = TonalSequenceState {
                phrase: self.active_phrase,
                notes: self.evolved_phrase.clone(),
                evolution_seed: self.evolution_seed,
                evolution_count: self.evolution_count,
            };
        });
    }
}

fn evolve_random(seed: u64, evolution_count: u64, draw: u64) -> u64 {
    splitmix64_mix(
        seed ^ evolution_count.wrapping_mul(0x9E37_79B9_7F4A_7C15)
            ^ draw.wrapping_mul(0xBF58_476D_1CE4_E5B9),
    )
}

pub(crate) fn tonal_phrase(phrase: usize) -> &'static [i32] {
    TONAL_PHRASES[phrase % TONAL_PHRASES.len()]
}

pub(crate) fn tonal_loop_len(cycle_beats: f32, rate_beats: f32) -> usize {
    (cycle_beats / tonal_rate_beats(rate_beats))
        .round()
        .clamp(1.0, TONAL_MAX_LOOP_STEPS as f32) as usize
}

pub(crate) fn tonal_cycle_index(beat: f64, cycle_beats: f32) -> u64 {
    let cycle = f64::from(tonal_cycle_beats(cycle_beats));
    (beat.max(0.0) / cycle).floor() as u64
}

pub(crate) fn tonal_cycle_step(beat: f64, cycle_beats: f32, rate_beats: f32) -> usize {
    let cycle = f64::from(tonal_cycle_beats(cycle_beats));
    let local = beat.rem_euclid(cycle);
    (local / f64::from(tonal_rate_beats(rate_beats))).floor() as usize
}

pub(crate) fn tonal_offset_step(offset_beats: f32, rate_beats: f32) -> usize {
    (offset_beats.max(0.0) / tonal_rate_beats(rate_beats)).floor() as usize
}

pub(crate) fn tonal_rate_beats(rate_beats: f32) -> f32 {
    rate_beats.clamp(TONAL_RATE_BEATS_MIN, TONAL_RATE_BEATS_MAX)
}

pub(crate) fn tonal_cycle_beats(cycle_beats: f32) -> f32 {
    cycle_beats.clamp(TONAL_CYCLE_BEATS_MIN, TONAL_CYCLE_BEATS_MAX)
}

pub(crate) fn tonal_evolve_note_count(rate: f32, phrase_len: usize) -> usize {
    if phrase_len == 0 || rate <= 0.0 {
        return 0;
    }
    (rate.clamp(0.0, 1.0) * TONAL_MAX_EVOLVE_NOTES as f32)
        .ceil()
        .min(phrase_len as f32) as usize
}

pub(crate) struct TonalLowCut {
    pub(crate) alpha: f32,
    pub(crate) last_input: f32,
    pub(crate) last_output: f32,
}

impl TonalLowCut {
    pub(crate) fn new(sample_rate: f32, cutoff_hz: f32) -> Self {
        let sample_rate = sample_rate.max(1.0);
        let cutoff_hz = cutoff_hz.max(1.0);
        let dt = 1.0 / sample_rate;
        let rc = 1.0 / (TAU * cutoff_hz);
        Self {
            alpha: rc / (rc + dt),
            last_input: 0.0,
            last_output: 0.0,
        }
    }

    pub(crate) fn process(&mut self, input: f32) -> f32 {
        let output = self.alpha * (self.last_output + input - self.last_input);
        self.last_input = input;
        self.last_output = output;
        output
    }
}

/// One note's trigger-time parameters, captured when its voice is created:
/// the pitch, where it sits in the stereo field, how loud it was triggered,
/// and the attack/decay that decide how long it sounds. Every synth type takes
/// exactly this set, so `synth_type` alone selects the character.
#[derive(Clone, Copy)]
pub(crate) struct TonalNote {
    /// MIDI note number. Piano profiles scale harmonics and decay with
    /// register from it; the sine voice has no register-dependent behavior and
    /// ignores it.
    pub(crate) midi: i32,
    pub(crate) hz: f32,
    pub(crate) pan: f32,
    pub(crate) sample_rate: f32,
    pub(crate) attack_time: f32,
    pub(crate) decay_time: f32,
}

pub(crate) enum TonalVoice {
    Sine(SineTonalVoice),
    Piano(Box<PianoTonalVoice>),
}

impl TonalVoice {
    /// A voice's whole life is `attack + decay` seconds: the amplitude ramps
    /// in over `attack`, then falls from the peak to silence over `decay`. The
    /// step grid only decides *when* the next note triggers, never how long
    /// this one sounds, so notes overlap freely when `decay` outlasts the step.
    pub(crate) fn new(synth_type: usize, note: TonalNote) -> Self {
        match synth_type {
            0 => Self::Sine(SineTonalVoice::new(note)),
            _ => Self::Piano(Box::new(PianoTonalVoice::new(
                piano_profile(synth_type),
                note,
            ))),
        }
    }

    pub(crate) fn next(&mut self) -> (f32, f32) {
        match self {
            Self::Sine(voice) => voice.next(),
            Self::Piano(voice) => voice.next(),
        }
    }

    pub(crate) fn is_done(&self) -> bool {
        match self {
            Self::Sine(voice) => voice.is_done(),
            Self::Piano(voice) => voice.is_done(),
        }
    }
}

/// Shape of the sine voice's decay taper: `sqrt(1 - t)`, i.e. a decay curve
/// exponent of 0.5.
const TONAL_SINE_DECAY_POWER: f32 = 0.5;

/// Attack + decay envelope shared by every tonal synth type — the one
/// foundational note shape. `elapsed`, `attack`, and `decay` are seconds:
/// the gain ramps 0->1 across the first `attack` seconds, then falls from the
/// peak back to 0 across the following `decay` seconds. A note's whole
/// sounding life is therefore `attack + decay`; the gain reaches exactly 0 at
/// that point, so a voice killed there ends in silence with no click. `power`
/// is the decay curve's shape exponent — the one piece of "harmonic
/// character" each voice keeps (the piano profile's `body_power`, or the sine
/// voice's fixed sqrt taper).
///
/// A control of exactly 0 means "instant": an attack of 0 reaches full volume
/// on the first sample, and a decay of 0 collapses the note to nothing. (The
/// registry floors `decay` above 0 so the UI can never request the hard,
/// clicking cut a literal 0 would produce.)
pub(crate) fn attack_decay_gain(elapsed: f32, attack: f32, decay: f32, power: f32) -> f32 {
    let attack_gain = if attack <= 0.0 {
        1.0
    } else {
        (elapsed / attack).clamp(0.0, 1.0)
    };

    let decay_gain = if decay <= 0.0 {
        0.0
    } else {
        let into_decay = (elapsed - attack).max(0.0);
        (1.0 - (into_decay / decay).clamp(0.0, 1.0)).powf(power)
    };

    attack_gain * decay_gain
}

/// The part of a tonal/arp note that is the same whatever synthesizes it:
/// its attack + decay lifetime clock, the shared `attack_decay_gain` envelope
/// at the voice's own decay `power`, and its pan. A voice keeps only its
/// oscillators next to one of these.
pub(crate) struct TonalNoteLife {
    samples_elapsed: u64,
    total_samples: u64,
    total_duration: f32,
    attack_time: f32,
    decay_time: f32,
    power: f32,
    pan_gains: (f32, f32),
}

impl TonalNoteLife {
    pub(crate) fn new(note: &TonalNote, power: f32) -> Self {
        let sample_rate = note.sample_rate.max(1.0);
        // The note's whole life is attack + decay; the envelope reaches zero
        // exactly at that point, so this length ends the voice in silence.
        let total = (((note.attack_time + note.decay_time) * sample_rate).round() as u64).max(1);
        Self {
            samples_elapsed: 0,
            total_samples: total,
            total_duration: total as f32 / sample_rate,
            attack_time: note.attack_time,
            decay_time: note.decay_time,
            power,
            pan_gains: StereoPanner::gains(note.pan),
        }
    }

    /// This sample's envelope gain, advancing the clock; `None` once the note
    /// has lived out its attack + decay.
    pub(crate) fn next_gain(&mut self) -> Option<f32> {
        if self.is_done() {
            return None;
        }
        let elapsed = self.samples_elapsed as f32 / self.total_samples as f32 * self.total_duration;
        self.samples_elapsed += 1;
        Some(attack_decay_gain(
            elapsed,
            self.attack_time,
            self.decay_time,
            self.power,
        ))
    }

    pub(crate) fn is_done(&self) -> bool {
        self.samples_elapsed >= self.total_samples
    }

    pub(crate) fn pan(&self, s: f32) -> (f32, f32) {
        (s * self.pan_gains.0, s * self.pan_gains.1)
    }
}

pub(crate) struct SineTonalVoice {
    pub(crate) primary: SineOscillator,
    pub(crate) detuned: SineOscillator,
    pub(crate) life: TonalNoteLife,
}

impl SineTonalVoice {
    pub(crate) fn new(note: TonalNote) -> Self {
        let sample_rate = note.sample_rate.max(1.0);
        Self {
            primary: SineOscillator::new(note.hz, sample_rate),
            detuned: SineOscillator::new(note.hz * 1.004, sample_rate),
            life: TonalNoteLife::new(&note, TONAL_SINE_DECAY_POWER),
        }
    }
    pub(crate) fn next(&mut self) -> (f32, f32) {
        let Some(gain) = self.life.next_gain() else {
            return (0.0, 0.0);
        };
        let s = soft_clip((self.primary.next() + self.detuned.next() * 0.3) * 0.4) * gain;
        self.life.pan(s)
    }
    pub(crate) fn is_done(&self) -> bool {
        self.life.is_done()
    }
}

pub(crate) struct PianoKeyframe {
    pub(crate) midi: i32,
    pub(crate) decay_factor: f32,
    pub(crate) harmonics: [f32; TONAL_PIANO_HARMONIC_COUNT],
}

#[derive(Clone, Copy)]
pub(crate) struct PianoProfile {
    pub(crate) keyframes: &'static [PianoKeyframe],
    pub(crate) amplitude: f32,
    pub(crate) body_power: f32,
    pub(crate) harmonic_tilt: f32,
    pub(crate) decay_low: f32,
    pub(crate) decay_high: f32,
    pub(crate) decay_scale: f32,
}

pub(crate) struct PianoTonalVoice {
    pub(crate) oscillators: [SineOscillator; TONAL_PIANO_HARMONIC_COUNT],
    pub(crate) profile: PianoProfile,
    pub(crate) harmonic_amplitudes: [f32; TONAL_PIANO_HARMONIC_COUNT],
    /// Per-sample multiplicative decay: `exp(-rate / total_samples)`, so
    /// running `harmonic_decay_state *= harmonic_decay_steps` each sample
    /// reproduces `exp(-t * rate)` without an `exp()` call per sample.
    pub(crate) harmonic_decay_steps: [f32; TONAL_PIANO_HARMONIC_COUNT],
    pub(crate) harmonic_decay_state: [f32; TONAL_PIANO_HARMONIC_COUNT],
    pub(crate) life: TonalNoteLife,
}

impl PianoTonalVoice {
    pub(crate) fn new(profile: PianoProfile, note: TonalNote) -> Self {
        let sample_rate = note.sample_rate.max(1.0);
        // The piano's natural per-harmonic rolloff normalizes to the decay
        // time alone, so `decay` sets how long the note rings and `attack`
        // never stretches (and slows) the timbre.
        let decay_samples = (((note.decay_time * sample_rate).round()) as u64).max(1);
        let harmonic_decay_rates = piano_harmonic_decay_rates(profile, note.midi, note.hz);
        Self {
            oscillators: std::array::from_fn(|index| {
                SineOscillator::new(note.hz * (index + 1) as f32, sample_rate)
            }),
            profile,
            harmonic_amplitudes: piano_harmonic_amplitudes(profile, note.midi),
            harmonic_decay_steps: harmonic_decay_rates
                .map(|rate| (-rate / decay_samples as f32).exp()),
            harmonic_decay_state: [1.0; TONAL_PIANO_HARMONIC_COUNT],
            life: TonalNoteLife::new(&note, profile.body_power),
        }
    }

    pub(crate) fn next(&mut self) -> (f32, f32) {
        let Some(envelope) = self.life.next_gain() else {
            return (0.0, 0.0);
        };

        let mut sample = 0.0f32;
        for index in 0..TONAL_PIANO_HARMONIC_COUNT {
            let harmonic = self.oscillators[index].next();
            let decay = self.harmonic_decay_state[index];
            self.harmonic_decay_state[index] *= self.harmonic_decay_steps[index];
            sample += harmonic * self.harmonic_amplitudes[index] * decay;
        }

        let s = soft_clip(sample * self.profile.amplitude) * envelope;
        self.life.pan(s)
    }

    pub(crate) fn is_done(&self) -> bool {
        self.life.is_done()
    }
}

pub(crate) fn piano_profile(synth_type: usize) -> PianoProfile {
    TONAL_PIANO_PROFILES[(synth_type.saturating_sub(1)) % TONAL_PIANO_PROFILES.len()]
}

pub(crate) fn piano_harmonic_amplitudes(
    profile: PianoProfile,
    midi_note: i32,
) -> [f32; TONAL_PIANO_HARMONIC_COUNT] {
    let (low, high) = piano_keyframe_pair(profile, midi_note);
    let t = ease_in_out(lerp_t(low.midi as f32, high.midi as f32, midi_note as f32));
    std::array::from_fn(|index| {
        let harmonic = (index + 1) as f32;
        let tilt = harmonic.powf(profile.harmonic_tilt);
        lerp(low.harmonics[index], high.harmonics[index], t) * tilt
    })
}

pub(crate) fn piano_harmonic_decay_rates(
    profile: PianoProfile,
    midi_note: i32,
    fundamental_hz: f32,
) -> [f32; TONAL_PIANO_HARMONIC_COUNT] {
    let (low, high) = piano_keyframe_pair(profile, midi_note);
    let t = ease_in_out(lerp_t(low.midi as f32, high.midi as f32, midi_note as f32));
    let frame_decay = lerp(low.decay_factor, high.decay_factor, t).max(0.25);
    std::array::from_fn(|index| {
        let harmonic_hz = fundamental_hz * (index + 1) as f32;
        let pitch_decay = lerp_t(80.0, 6_000.0, harmonic_hz);
        lerp(profile.decay_low, profile.decay_high, pitch_decay) * profile.decay_scale / frame_decay
    })
}

fn piano_keyframe_pair(
    profile: PianoProfile,
    midi_note: i32,
) -> (&'static PianoKeyframe, &'static PianoKeyframe) {
    let mut low = &profile.keyframes[0];
    let mut high = &profile.keyframes[profile.keyframes.len() - 1];

    for keyframe in profile.keyframes {
        if keyframe.midi <= midi_note && keyframe.midi >= low.midi {
            low = keyframe;
        }
        if keyframe.midi >= midi_note && keyframe.midi <= high.midi {
            high = keyframe;
        }
    }

    (low, high)
}

fn lerp_t(min: f32, max: f32, value: f32) -> f32 {
    if (max - min).abs() <= f32::EPSILON {
        0.0
    } else {
        ((value - min) / (max - min)).clamp(0.0, 1.0)
    }
}

fn lerp(a: f32, b: f32, t: f32) -> f32 {
    a + (b - a) * t
}

fn ease_in_out(t: f32) -> f32 {
    if t < 0.5 {
        2.0 * t * t
    } else {
        1.0 - (-2.0 * t + 2.0).powi(2) * 0.5
    }
}