makeover_tui/

piece.rs

//! The pieces every terminal app draws, drawn once.
//!
//! # Not `widget`
//!
//! `makeover-layout` owns that word for something else, and the two meanings do
//! not sit together. A `Region::Widget` there is host-agnostic: a named
//! assembly of primitives that every renderer draws its own way. What is in
//! this module is the opposite end, renderer-local, the answer to *what a meter
//! looks like in cells*, taking a description plus what only a terminal knows.
//! The style type is `PieceStyle`.
//!
//! A meter, a badge, a control, a figure and a form field are what a screen is
//! made of below the level [`table`](crate::table) works at. [`activity`] and
//! [`awaiting`] draw a wait, out of wiki `loading-and-progress-standard`.
//!
//! # What these take, and what they leave alone
//!
//! Each takes a `makeover-layout` description, a [`PieceStyle`], and whatever
//! the *host* knows that a description never carries. That last part is the
//! shape worth copying: [`field`] takes what is currently typed in the box as a
//! separate argument, because [`Field`] deliberately does not carry a value and
//! is not going to. `makeover-immediate` reached the same seam from the other
//! side with its `Filling`, and [`Held`] is that seam here.
//!
//! Focus is the other one. Nothing in a description says which control the user
//! is on, so every drawing here takes `focused` as an argument and the caller
//! is what counts. What focus *looks like* is this crate's answer and not the
//! caller's, which is the point of it being here: see
//! [`PieceStyle::focused`].
//!
//! # What they do not do
//!
//! No layout. Each answers rows for a width, or draws into the rect it is
//! given, top-aligned, and never below it. Nothing here measures twice and
//! nothing here places anything relative to anything else, because the moment
//! it did it would be a layout engine with one consumer's flow baked into it.

use makeover_layout::{
    Act, Awaiting, Bar, Chart, Field, FieldKind, Figure, Heading, Meter, ThemeVariant, Token, Tone,
};
use ratatui::buffer::Buffer;
use ratatui::layout::Rect;
use ratatui::style::{Modifier, Style};
use ratatui::text::{Line, Span};

use crate::text;
use std::time::Duration;

/// The colours and marks the drawings below use.
///
/// [`TableStyle`](crate::table::TableStyle)'s shape, for its reasons: an
/// ungated struct of styles with a [`Default`], plus a
/// [`from_theme`](Self::from_theme) that is what a consumer holding a loaded
/// theme should reach for first. A consumer painting bevels and nothing else
/// should not have to supply text tones it never uses, and gating the whole
/// module on `theme` would make these unreachable to anyone hand-picking
/// colours.
///
/// The default is the one that survives a terminal with no colour at all:
/// modifiers only, no foreground anywhere. That is not a placeholder. A
/// two-colour terminal is the case where a `Style` carrying a foreground is a
/// foreground that will not land, and bold-and-reversed is what is left.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct PieceStyle {
    /// Ordinary content, and what [`Tone::Neutral`] reads as.
    pub content: Style,
    /// Content one step back: a field's label, a quoted run.
    pub secondary: Style,
    /// Content two steps back: a caption, a hint, a meter's reading.
    pub muted: Style,
    /// Something worth knowing and nothing to do about it.
    pub info: Style,
    /// Something finished and it worked.
    pub success: Style,
    /// Something the user should look at.
    pub warning: Style,
    /// Something broken, or about to be destroyed.
    pub danger: Style,
    /// A page title.
    pub page: Style,
    /// A section title.
    pub section: Style,
    /// A subsection title.
    pub subsection: Style,
    /// Text that goes somewhere, and a control's label.
    pub action: Style,
    /// A control filled with the action colour, for the one on a screen that is
    /// the thing to press. A form's submit is the case that has it.
    pub filled: Style,
    /// A surface set back from the one it sits on, by colour and nothing else.
    /// What a code run takes, since every cell is monospace and the thing a
    /// webview says with a typeface cannot be said that way here.
    pub sunken: Style,
    /// What "you are on this one" adds to whatever it lands on.
    ///
    /// Reversed video by default, which is the affordance a cell has left once
    /// colour is spent on tone and bold on weight. A webview says it with an
    /// outline; a terminal has no outline that is not four more cells.
    pub focus: Modifier,
    /// How many cells [`meter`] spends on its bar.
    pub meter_cells: u16,
    /// The filled part of a bar.
    pub meter_full: char,
    /// The empty part of a bar.
    pub meter_empty: char,
    /// What marks a compulsory field, appended to its label.
    ///
    /// A knob for `makeover-immediate`'s reason: it is the one piece of *copy*
    /// here, and copy is not a renderer's call.
    pub required_marker: &'static str,
}

impl Default for PieceStyle {
    /// Modifiers only, no foreground: what survives a terminal with two
    /// colours.
    fn default() -> Self {
        Self {
            content: Style::new(),
            secondary: Style::new(),
            muted: Style::new().add_modifier(Modifier::DIM),
            info: Style::new(),
            success: Style::new(),
            warning: Style::new(),
            danger: Style::new().add_modifier(Modifier::BOLD),
            page: Style::new().add_modifier(Modifier::BOLD),
            section: Style::new().add_modifier(Modifier::BOLD),
            subsection: Style::new(),
            action: Style::new().add_modifier(Modifier::UNDERLINED),
            filled: Style::new().add_modifier(Modifier::REVERSED),
            sunken: Style::new().add_modifier(Modifier::DIM),
            focus: Modifier::REVERSED,
            meter_cells: 10,
            meter_full: '#',
            meter_empty: '-',
            required_marker: "*",
        }
    }
}

impl PieceStyle {
    /// The house widgets, from a loaded theme.
    ///
    /// The lift this module exists for. `quasi-tui` carried every line of this
    /// as private methods on its own renderer; a second terminal app wanting a
    /// toned control had no way to reach them and would have picked its own
    /// colours for the same five tones.
    #[cfg(feature = "theme")]
    #[must_use]
    pub fn from_theme(theme: &crate::Theme) -> Self {
        Self {
            content: Style::new().fg(theme.content_primary),
            secondary: Style::new().fg(theme.content_secondary),
            muted: Style::new().fg(theme.content_muted),
            info: Style::new().fg(theme.status_info),
            success: Style::new().fg(theme.status_success),
            warning: Style::new().fg(theme.status_warning),
            danger: Style::new().fg(theme.status_danger),
            // Three depths and two of them are bold, which is the whole of what
            // a terminal has: there is no type scale in a grid of one cell
            // size. A page title takes bold and the accent, a section bold, a
            // subsection the secondary colour. That is the emphasis order a
            // webview's type scale says with size, said with the two axes a
            // cell has.
            page: Style::new()
                .fg(theme.action_primary)
                .add_modifier(Modifier::BOLD),
            section: Style::new()
                .fg(theme.content_primary)
                .add_modifier(Modifier::BOLD),
            subsection: Style::new().fg(theme.content_secondary),
            action: Style::new().fg(theme.action_primary),
            filled: Style::new().fg(theme.selection_on).bg(theme.action_primary),
            sunken: Style::new().bg(theme.surface_sunken),
            focus: Modifier::REVERSED,
            meter_cells: 10,
            meter_full: '#',
            meter_empty: '-',
            required_marker: "*",
        }
    }

    /// The style a tone reads as.
    ///
    /// [`Tone`] is closed and stays closed, so this is total and needs no
    /// fallback arm.
    #[must_use]
    pub const fn tone(&self, tone: Tone) -> Style {
        match tone {
            Tone::Neutral => self.content,
            Tone::Info => self.info,
            Tone::Success => self.success,
            Tone::Warning => self.warning,
            Tone::Danger => self.danger,
        }
    }

    /// The style a heading reads as.
    #[must_use]
    pub const fn heading(&self, level: Heading) -> Style {
        match level {
            Heading::Page => self.page,
            Heading::Section => self.section,
            Heading::Subsection => self.subsection,
        }
    }

    /// `style`, plus the mark that says the user is on this one.
    ///
    /// Takes the flag rather than being called behind an `if`, because every
    /// caller has a bool in hand and the branch is the part that gets forgotten.
    #[must_use]
    pub fn focused(&self, focused: bool, style: Style) -> Style {
        if focused {
            style.add_modifier(self.focus)
        } else {
            style
        }
    }
}

/// What a field currently holds, which a description never carries.
///
/// The terminal counterpart of `makeover_immediate::Filling`, and the same seam:
/// there the widget writes through a `&mut` as the value is edited, and here the
/// caller keeps an edit buffer and lends it out for the draw. Neither is
/// something [`Field`] could carry without becoming a form model.
///
/// An enum rather than a bag of options, for `Filling`'s reason: a checkbox
/// holding a string is unsayable here, where a struct would let it be said and
/// then have to cope.
#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
pub enum Held<'a> {
    /// Nothing typed and nothing chosen. The control draws empty.
    #[default]
    Absent,
    /// What is in the box, or the `value` of the chosen [`Choice`].
    ///
    /// [`Choice`]: makeover_layout::Choice
    Text(&'a str),
    /// A checkbox, on or off.
    On(bool),
    /// Both ends of a [`FieldKind::Interval`], lower first.
    ///
    /// Two values rather than one string with a separator, which is
    /// [`makeover_layout::Field::upper_name`]'s reason one level down: an
    /// interval is submitted under two names, so it is held as two values, and
    /// a delimiter this crate owned could appear inside either of them.
    ///
    /// Either end may be empty while the other stands. An open end is an
    /// answer -- "over 120 BPM" -- rather than a half-filled box.
    Between {
        /// What the lower box holds now.
        lower: &'a str,
        /// What the upper box holds now.
        upper: &'a str,
    },
}

impl<'a> Held<'a> {
    /// What is typed, as a string. A checkbox has no text and answers empty.
    #[must_use]
    pub const fn text(self) -> &'a str {
        match self {
            Self::Text(text) | Self::Between { lower: text, .. } => text,
            Self::Absent | Self::On(_) => "",
        }
    }

    /// The upper end, for the one variant that has one.
    #[must_use]
    pub const fn upper(self) -> &'a str {
        match self {
            Self::Between { upper, .. } => upper,
            Self::Absent | Self::Text(_) | Self::On(_) => "",
        }
    }

    /// Whether a checkbox is ticked.
    #[must_use]
    pub const fn on(self) -> bool {
        matches!(self, Self::On(true))
    }
}

/// What a host can see about a wait that is running.
///
/// Neither half is derivable from a description, which is why both are here and
/// not on [`Awaiting`]. That type says how big the payload is; how much of it
/// has landed is a fact about a transfer in flight, and only whoever is running
/// the transfer knows it.
///
/// The same shape `makeover-immediate` carries, deliberately: a wait is one
/// reading on every surface and the two renderers should not disagree about
/// what a host owes them.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub struct Progress {
    /// How much has arrived, in whatever unit the description counted.
    pub delivered: Option<u64>,
    /// How long the wait has lasted so far.
    ///
    /// The one time value a wait may show. See [`awaiting`] for the three it
    /// may not.
    pub elapsed: Option<Duration>,
}

/// The activity mark: one cell, lit or dark.
///
/// Rule 2 of wiki `loading-and-progress-standard`, and the surface the metaphor
/// came from. A hard-disk light is one cell that blinks, and a terminal draws
/// that with no metaphor in the way — where a webview needs a keyframe and egui
/// needs a repaint schedule, this is a character.
///
/// The two glyphs are [`PieceStyle::meter_full`] and
/// [`PieceStyle::meter_empty`], not a third pair. A bar's filled cell and a lit
/// mark are the same statement in the same alphabet, and a terminal that had to
/// render two vocabularies of "on" would be saying there are two kinds of on.
///
/// **Dark, not absent.** A mark that is drawn half the time is a hole in the
/// line, and the line reflows around it or the reader loses where to look. It
/// occupies its cell either way.
///
/// `lit` is the caller's: this module holds no clock. [`crate::activity_lit`]
/// is the one place the phase is worked out from the cadence, so a caller
/// should reach for that rather than dividing by 500 itself.
#[must_use]
pub fn activity(style: &PieceStyle, lit: bool) -> Span<'static> {
    if lit {
        Span::styled(style.meter_full.to_string(), style.action)
    } else {
        Span::styled(style.meter_empty.to_string(), style.muted)
    }
}

/// A wait as one line, drawn from what is actually known about it.
///
/// [`Awaiting::is_determinate`] is the first branch and there is a second the
/// description cannot answer: whether anything is watching the transfer. A bar
/// wants a total and a numerator both, so a described amount with no
/// [`Progress::delivered`] beside it draws the mark and the size it is waiting
/// on, rather than an empty trough implying somebody is counting.
///
/// So three drawings for three states, which is the point:
///
/// ```text
/// unmeasured                       #            a blinking cell
/// measured, nothing watching       # 41943040   the cell, and how much there is
/// measured and observed            ####------ 17825792/41943040  4s
/// ```
///
/// **What the bar may not do**, from rule 1 of the standard and from
/// [`Awaiting`]'s own docs: what is done over what there is, plus the time it
/// has taken. Never a remaining time, an arrival time, or a rate extrapolated
/// forward. A prediction is wrong the moment the transfer stalls, and being
/// confidently wrong is worse than being honestly indeterminate.
///
/// The numbers are raw. The unit is the app's — bytes for an upload, rows for
/// an import — and a renderer that formatted one as a file size would be
/// dressing up a quantity it was deliberately not told about.
#[must_use]
pub fn awaiting(
    style: &PieceStyle,
    awaiting: Awaiting,
    progress: Progress,
    lit: bool,
) -> Line<'static> {
    let Some(total) = awaiting.amount else {
        return Line::from(vec![activity(style, lit)]);
    };
    let Some(done) = progress.delivered else {
        return Line::from(vec![
            activity(style, lit),
            Span::styled(format!(" {total}"), style.muted),
        ]);
    };
    let cells = u32::from(style.meter_cells);
    // In cells rather than in floating point, the way `meter` does it: a
    // terminal's bar has ten states and rounding through an f64 to reach one of
    // ten is arithmetic nobody needs. Saturating rather than wrapping, because
    // a transfer that over-delivers is a real case and a panicking bar is not
    // the way to report it.
    let filled = u32::try_from(
        done.saturating_mul(u64::from(cells))
            .checked_div(total)
            .unwrap_or(0),
    )
    .unwrap_or(cells)
    .min(cells);
    let bar = format!(
        "{}{}",
        style.meter_full.to_string().repeat(filled as usize),
        style
            .meter_empty
            .to_string()
            .repeat((cells - filled) as usize)
    );
    let reading = match progress.elapsed {
        Some(elapsed) => format!(" {done}/{total}  {}s", elapsed.as_secs()),
        None => format!(" {done}/{total}"),
    };
    Line::from(vec![
        Span::styled(bar, style.action),
        Span::styled(reading, style.muted),
    ])
}

/// A proportion as one line: the bar, then the reading beside it.
///
/// The reading is built here from the two numbers and the noun rather than
/// taken assembled, which is what [`Meter::label`] carrying the noun alone is
/// for: a terminal at one line and a tooltip want different sentence orders.
#[must_use]
pub fn meter(style: &PieceStyle, meter: &Meter<'_>) -> Line<'static> {
    let cells = u32::from(style.meter_cells);
    let filled = meter
        .done
        .checked_mul(cells)
        .and_then(|reached| reached.checked_div(meter.total))
        .unwrap_or(0)
        .min(cells);
    let bar = format!(
        "{}{}",
        style.meter_full.to_string().repeat(filled as usize),
        style
            .meter_empty
            .to_string()
            .repeat((cells - filled) as usize)
    );
    let reading = match meter.label {
        Some(label) => format!(" {}/{} {label}", meter.done, meter.total),
        None => format!(" {}/{}", meter.done, meter.total),
    };
    Line::from(vec![
        Span::styled(bar, style.tone(meter.tone)),
        Span::styled(reading, style.muted),
    ])
}

/// A badge or a chip as one span.
///
/// Round for a badge, square for a chip. A chip answers a press and a badge does
/// not, and the bracket is the only affordance a cell has left once colour is
/// spent on the tone.
///
/// `latched` is a chip that is switched on, and it reads as reversed. So does
/// focus, which is a collision a terminal cannot avoid: latched is "this filter
/// is on" and focused is "you are here", and there is one spare axis for two
/// facts. Said here rather than resolved by inventing a third look nobody would
/// read.
///
/// A chip's removable half is not drawn. The `x` a webview hangs on a chip is a
/// second control inside one span, and a terminal reaches a control by focusing
/// it; two targets in one cell run is a question for whoever owns the
/// interaction, not for a drawing.
#[must_use]
pub fn token(
    style: &PieceStyle,
    label: &str,
    kind: Token,
    tone: Tone,
    latched: bool,
    focused: bool,
) -> Span<'static> {
    let painted = style.tone(tone);
    let painted = if latched {
        painted.add_modifier(style.focus)
    } else {
        style.focused(focused, painted)
    };
    match kind {
        Token::Badge => Span::styled(format!("({label})"), painted),
        Token::Chip { .. } => Span::styled(format!("[{label}]"), painted),
    }
}

/// A control as one line.
///
/// `< Label > (key)`, and the key only where the description named one. That
/// member is the one place `makeover-layout` anticipated a terminal before there
/// was one, and this is the renderer that reads it.
///
/// A disabled control is drawn muted and is not marked focused, whatever the
/// caller passed: it is present, visible and not answering, so a focus mark on
/// it would be an affordance that lies. Whether it is reachable at all is the
/// caller's count to keep — ask [`Act::disabled`].
#[must_use]
pub fn act(style: &PieceStyle, act: &Act<'_>, focused: bool) -> Line<'static> {
    let painted = if act.disabled() {
        style.muted
    } else {
        style.focused(focused, style.tone(act.tone))
    };
    let label = match act.key {
        Some(key) => format!("< {} > ({key})", act.label),
        None => format!("< {} >", act.label),
    };
    Line::from(Span::styled(label, painted))
}

/// The muted line a control's [`Act::hint`] draws as, or `None` where it has
/// none.
///
/// A terminal has no pointer, so the hover the other two renderers spend a hint
/// on is not available and is not the thing anyway: what the description says
/// is that the sentence is true, never that it is hidden. A row under the
/// control is this renderer's answer, and it is the same muted row
/// [`field`] gives a field's note, so the two read alike wherever they land.
///
/// Its own function rather than extra lines out of [`act`], because a control
/// is one [`Line`] everywhere it is drawn and a caller laying out a run needs
/// to know it is placing two things.
#[must_use]
pub fn act_note(style: &PieceStyle, act: &Act<'_>) -> Option<Line<'static>> {
    act.hint
        .map(|hint| Line::from(Span::styled(hint.to_owned(), style.muted)))
}

/// A control filled with the action colour, for the one press a screen is about.
///
/// `[ Label ]` rather than `< Label >`, which is the weight difference a webview
/// carries as a primary-versus-secondary button. A form's submit is the case
/// this exists for.
#[must_use]
pub fn filled_act(style: &PieceStyle, label: &str, focused: bool) -> Line<'static> {
    Line::from(Span::styled(
        format!("[ {label} ]"),
        style.focused(focused, style.filled),
    ))
}

/// The rows [`figure`] wants at `width`.
#[must_use]
pub fn figure_height(figure: &Figure<'_>, width: u16) -> u16 {
    text::height(figure.value, width) + text::height(figure.caption, width)
}

/// A figure: the number, then what it counts under it.
///
/// The tone lands on the value and its change rather than on the caption, which
/// is what [`Figure::tone`] means: the figure is an ordinary fact and it is the
/// movement that reads as good or bad.
pub fn figure(style: &PieceStyle, figure: &Figure<'_>, area: Rect, buf: &mut Buffer) -> u16 {
    let value = match figure.change {
        Some(change) => format!("{} {change}", figure.value),
        None => figure.value.to_owned(),
    };
    let used = text::draw(
        &value,
        style.tone(figure.tone).add_modifier(Modifier::BOLD),
        area,
        buf,
    );
    used + text::draw(figure.caption, style.muted, below(area, used), buf)
}

/// The rows [`field`] wants at `width`.
///
/// A label row, the control's rows, and a row for whatever went wrong. A hidden
/// field is nothing at all, which is the one field kind a terminal and a webview
/// agree on completely.
#[must_use]
pub fn field_height(style: &PieceStyle, field: &Field<'_>, width: u16) -> u16 {
    if !field.kind.visible() {
        return 0;
    }
    let label = text::height(&label_of(style, field), width);
    // A range is one row like every other single control: the bar, its two ends
    // and the reading are one line by construction, and a bar that wrapped
    // would stop being a bar.
    let body = match field.kind {
        // Both multi-line kinds get the same three rows, keyed on the
        // description's own `multiline` rather than on the member: a markdown
        // field falling through to the single-row arm is one line for a value
        // whose whole point is that it has several. What a terminal does *with*
        // the markdown is another question and the answer here is nothing --
        // the source is the text, and drawing it as text is honest.
        kind if kind.multiline() => 3,
        kind if kind.offers_options() => u16::try_from(field.options.len()).unwrap_or(u16::MAX),
        // A row per theme, a row per group heading, and a row for the follow
        // entry when there is one. The headings are counted by walking the
        // variants rather than by assuming three, because a machine with only
        // dark themes installed draws one heading and reserving three would
        // leave two blank rows under every picker.
        kind if kind.offers_themes() => {
            let mut variants = 0u16;
            let mut open: Option<ThemeVariant> = None;
            for theme in field.themes {
                if open != Some(theme.variant) {
                    variants = variants.saturating_add(1);
                    open = Some(theme.variant);
                }
            }
            let rows = u16::try_from(field.themes.len()).unwrap_or(u16::MAX);
            rows.saturating_add(variants)
                .saturating_add(u16::from(field.follows.is_some()))
        }
        _ => 1,
    };
    let note = message_of(style, field).map_or(0, |(text, _)| text::height(text, width));
    label + body + note
}

/// A question: its label, the box, and its standing help or what is wrong now.
///
/// `held` is what the user has done to it since the screen arrived, which is the
/// argument a description cannot supply. See [`Held`].
///
/// `focused` marks the box rather than the label, because the box is where the
/// typing lands.
///
/// [`makeover_layout::Field::as_instant`] is carried and not honoured. It asks
/// for a wall-clock value to be submitted as the moment it names, and this
/// renderer has no submission: it draws the box and the runtime above it
/// gathers what a submit sends, so the conversion belongs where that gathering
/// happens. The value drawn and read here is the local one, in
/// `makeover_layout::DATETIME_FORMAT`.
pub fn field(
    style: &PieceStyle,
    field: &Field<'_>,
    held: Held<'_>,
    focused: bool,
    area: Rect,
    buf: &mut Buffer,
) -> u16 {
    // A hidden field is data travelling with the form. There is nothing to
    // draw, and whoever submits carries it.
    if !field.kind.visible() || area.width == 0 || area.height == 0 {
        return 0;
    }

    let mut used = text::draw(&label_of(style, field), style.secondary, area, buf);

    let well = style.focused(focused, style.content);
    let placeholder = field.placeholder.unwrap_or_default();

    used += match field.kind {
        FieldKind::Checkbox => text::draw(
            if held.on() { "[x]" } else { "[ ]" },
            well,
            below(area, used),
            buf,
        ),
        // A range's two ends are what the question means, so they are drawn
        // rather than left to a hint. A terminal has the bar already: this is
        // `meter`'s cells with the extent read out at either side of them.
        //
        // An unbounded range has no extent to draw and falls through to the
        // text path, which is `makeover-immediate`'s answer as well and for the
        // same reason: bounds this crate invented are bounds the user would
        // then drag against.
        FieldKind::Range if field.bounded() => {
            let line = range_line(style, field, held.text(), well);
            text::draw_line(&line, below(area, used), buf)
        }
        // One question, so one line. The two ends read left to right with the
        // word between them, which is what a terminal has instead of two boxes
        // side by side: a second row would read as a second question, and that
        // is the reading the kind exists to prevent.
        FieldKind::Interval => {
            let line = interval_line(style, field, held, well);
            text::draw_line(&line, below(area, used), buf)
        }
        // The grouping comes out of the order, not out of a group list:
        // `Field::themes` arrives sorted by variant, so the run of one variant
        // is the group and a heading opens whenever the variant changes. Same
        // walk the other two renderers do, which is what keeps three renderers
        // from disagreeing about where a group starts.
        //
        // Drawn as the radio group above rather than as a closed control,
        // because a terminal has no closed control: the list is already on
        // screen and always was, so the group headings cost a row each and buy
        // the structure the description finally carries.
        kind if kind.offers_themes() => {
            let mut rows = 0;
            if let Some(follow) = field.follows {
                // First, and under no heading. It names no theme and sits in no
                // variant, so a heading over it would be inventing a fourth
                // variant for one row.
                let chosen = held.text() == follow.value;
                let (mark, painted) = if chosen {
                    ("(*)", well)
                } else {
                    ("( )", style.secondary)
                };
                rows += text::draw(
                    &format!("{mark} {}", follow.label),
                    painted,
                    below(area, used + rows),
                    buf,
                );
            }
            let mut open: Option<ThemeVariant> = None;
            for theme in field.themes {
                if open != Some(theme.variant) {
                    // Muted, which is the one place it is the truth rather than
                    // the lie: a heading will not answer, exactly as an
                    // unavailable option will not.
                    rows += text::draw(
                        theme.variant.heading(),
                        style.muted,
                        below(area, used + rows),
                        buf,
                    );
                    open = Some(theme.variant);
                }
                let chosen = held.text() == theme.id;
                let (mark, painted) = if chosen {
                    ("(*)", well)
                } else {
                    ("( )", style.secondary)
                };
                rows += text::draw(
                    &format!("{mark} {} [{}]", theme.name, theme.contrast.badge()),
                    painted,
                    below(area, used + rows),
                    buf,
                );
            }
            rows
        }
        kind if kind.offers_options() => {
            let mut rows = 0;
            for choice in field.options {
                let chosen = held.text() == choice.value;
                // An option that cannot be picked yet reads as inert, which is
                // the one place muted is the truth rather than the lie below:
                // it will not answer, and the reason it will not is on the row
                // beside it rather than nowhere.
                let (mark, painted, suffix) = match choice.unavailable {
                    Some(reason) => ("( )", style.muted, format!(": {reason}")),
                    None if chosen => ("(*)", well, String::new()),
                    // An option that is not chosen is still an option: pressing
                    // it chooses it. So it takes the secondary content intent
                    // and not the muted one, which is what disabled looks like
                    // (`State::Disabled` resolves to it). Muted here read as a
                    // list of five where four were greyed out.
                    None => ("( )", style.secondary, String::new()),
                };
                rows += text::draw(
                    &format!("{mark} {}{suffix}", choice.label),
                    painted,
                    below(area, used + rows),
                    buf,
                );
                // What picking it means, on a row of its own under the option.
                // makeover-layout 0.39.0, and this is the host with the most
                // room of the three: a browser's `<select>` has to run the line
                // into the option's text and a terminal does not, so it does
                // not.
                //
                // Indented past the mark, so the line reads as belonging to the
                // option above it rather than as another option. Muted, which
                // is the truth here rather than the lie the arms above are
                // careful about: the row is not a thing to press.
                if let Some(detail) = choice.detail {
                    rows += text::draw(detail, style.muted, indented(area, used + rows), buf);
                }
            }
            rows
        }
        // A secret's dots come from the caller's buffer and can come from
        // nowhere else: a password that comes back down the wire is a password
        // in a page and in a proxy log, so a description carries nothing to dot
        // out. This is the one control that would be undrawable without `held`.
        FieldKind::Secret if !held.text().is_empty() => {
            let dots = "*".repeat(held.text().chars().count());
            text::draw(&dots, well, below(area, used), buf).max(1)
        }
        // A file field has no way back on a terminal any more than it has on an
        // HTTP host. The name is drawn and picking one belongs to whoever owns
        // the interaction.
        //
        // makeover-layout 0.31.0 gave the description an accept list and a
        // multiplicity, and neither changes anything drawn here. Both are the
        // picker's business, and the picker is the caller's: this crate draws
        // what was picked. A terminal that grows its own picker reads them off
        // `Field::accept` and `Field::multiple` at that point rather than
        // through a second spelling invented here.
        _ if held.text().is_empty() => {
            empty_well(style, placeholder, well, focused, below(area, used), buf)
        }
        _ => text::draw(&measured(field, held.text()), well, below(area, used), buf),
    };

    // Error, then note, then hint -- the order `Field::note` names, and the
    // order a webview draws them in. Once something has gone wrong that is the
    // sentence worth the row; failing that, what the chosen answer costs beats
    // standing help about how the field works.
    match message_of(style, field) {
        Some((text, painted)) => used + text::draw(text, painted, below(area, used), buf),
        None => used,
    }
}

/// A bounded number as one line: the low end, the bar, the high end, then what
/// it currently reads.
///
/// The two ends are drawn because they are the question. A threshold of 0.72
/// says nothing without them, which is the whole argument for
/// [`FieldKind::Range`] being a kind rather than a number with bounds, and a
/// terminal is where it would be easiest to quietly drop them and show a figure.
///
/// The bar is [`meter`]'s cells, so a range and a proportion read as the same
/// object in the same app. What differs is the reading beside it: a meter counts
/// something and a range holds a value.
///
/// A value the host cannot read as a number empties the bar and is still shown
/// as itself. That is [`empty_well`]'s position on an unreadable value: the app
/// put it there, and a terminal that silently rounded it to a bound would be
/// reporting a value nobody set.
fn range_line(style: &PieceStyle, field: &Field<'_>, value: &str, well: Style) -> Line<'static> {
    let cells = usize::from(style.meter_cells);
    let ends = field
        .min
        .zip(field.max)
        .and_then(|(min, max)| Some((min.parse::<f64>().ok()?, max.parse::<f64>().ok()?)));
    let filled = match (ends, value.parse::<f64>()) {
        (Some((min, max)), Ok(number)) if max > min => {
            // Where the value sits is the curve's answer, not a proportion of
            // the extent (makeover-layout 0.32.0). Under `Curve::Linear` the two
            // are the same number, which is why the bar was right before and is
            // unchanged for every range described so far; under a constant ratio
            // they are not, and a bar drawn linearly would put an envelope's
            // whole useful half inside its first cell.
            #[expect(
                clippy::cast_possible_truncation,
                clippy::cast_sign_loss,
                reason = "`position_of` returns 0..=1, and the cell count came from a u16"
            )]
            let reached = (field.curve.position_of(number, min, max) * cells as f64) as usize;
            reached.min(cells)
        }
        _ => 0,
    };
    let bar = format!(
        "{}{}",
        style.meter_full.to_string().repeat(filled),
        style.meter_empty.to_string().repeat(cells - filled)
    );
    Line::from(vec![
        Span::styled(format!("{} ", field.min.unwrap_or_default()), style.muted),
        Span::styled(bar, well),
        Span::styled(format!(" {}", field.max.unwrap_or_default()), style.muted),
        Span::styled(format!(" {}", measured(field, value)), well),
    ])
}

/// An interval as one line: the low end, the word, the high end.
///
/// One line because it is one question. Two rows would read as two questions,
/// which is exactly what [`FieldKind::Interval`] exists to stop the description
/// saying, and a terminal has no side-by-side boxes to fall back on.
///
/// # An open end draws the bound it falls back to
///
/// Muted, because it is where the axis ends rather than a value anybody set.
/// With no bound to fall back on there is nothing honest to draw and the end
/// stays blank: a terminal inventing a number here would report a filter the
/// user never applied, which is [`range_line`]'s position on an unreadable
/// value.
///
/// # The word, not a dash
///
/// A dash between two numbers is a minus sign to anyone reading a signed axis,
/// and half the measured axes are signed -- audiofiles filters loudness in
/// dBFS. `to` costs two cells and cannot be misread.
fn interval_line(
    style: &PieceStyle,
    field: &Field<'_>,
    held: Held<'_>,
    well: Style,
) -> Line<'static> {
    let end = |value: &str, fallback: Option<&str>| match (value.is_empty(), fallback) {
        (false, _) => Span::styled(measured(field, value), well),
        (true, Some(bound)) => Span::styled(measured(field, bound), style.muted),
        (true, None) => Span::styled(String::new(), style.muted),
    };
    Line::from(vec![
        end(held.text(), field.min),
        Span::styled(" to ", style.secondary),
        end(held.upper(), field.max),
    ])
}

/// The unit to draw beside this field's value, if there is one to draw.
///
/// Two conditions rather than one: the field has to carry a unit and its kind
/// has to be one that means anything by it. `FieldKind::measurable` is the
/// description answering the second, so this renderer keeps no list of its own
/// of which kinds are quantities.
fn unit_of<'a>(field: &Field<'a>) -> Option<&'a str> {
    field.unit.filter(|_| field.kind.measurable())
}

/// A value with what it is measured in, as one string.
///
/// The unit rides on the value rather than on the label, which is what a
/// terminal wants: the label is a line above and the number is the line the eye
/// is on.
fn measured(field: &Field<'_>, value: &str) -> String {
    match unit_of(field) {
        Some(unit) => format!("{value} {unit}"),
        None => value.to_owned(),
    }
}

/// The label, marked where the field is compulsory.
fn label_of(style: &PieceStyle, field: &Field<'_>) -> String {
    if field.required {
        format!("{} {}", field.label, style.required_marker)
    } else {
        field.label.to_owned()
    }
}

/// What goes under the box, and how it is painted.
///
/// A terminal field has room for exactly one line, so the three message
/// channels compete for it and the precedence is decided in
/// [`makeover_layout::Field::note`]'s docs rather than three times here:
/// **error, then note, then hint**. What is wrong outranks what the answer
/// costs, which outranks how the field works.
///
/// The tone comes with the note; an error is always danger and a hint is
/// always muted, because neither carries one.
fn message_of<'a>(style: &PieceStyle, field: &Field<'a>) -> Option<(&'a str, Style)> {
    if let Some(error) = field.error {
        return Some((error, style.danger));
    }
    if let Some((tone, note)) = field.note {
        return Some((note, style.tone(tone)));
    }
    field.hint.map(|hint| (hint, style.muted))
}

/// A box with nothing in it: the ghost text, and the caret when it has focus.
///
/// The caret is not decoration. An empty field under a style is an empty field,
/// so a focused one with no placeholder drew literally nothing and there was no
/// way to tell the box was where the typing would go. A browser has a blinking
/// bar for this and gets it without asking; a terminal has one cell of reversed
/// video, put on the first column, which is where the first character lands.
fn empty_well(
    style: &PieceStyle,
    placeholder: &str,
    well: Style,
    focused: bool,
    area: Rect,
    buf: &mut Buffer,
) -> u16 {
    let used = text::draw(placeholder, style.muted, area, buf).max(1);
    if focused
        && area.height > 0
        && area.width > 0
        && let Some(cell) = buf.cell_mut((area.x, area.y))
    {
        cell.set_style(well);
    }
    used
}

/// What is left of `area` after `used` rows from the top.
/// The rows under what has been drawn, inset by the width of an option's mark.
///
/// An option's second line has to read as belonging to the option above it rather than as another option, and the only thing that
/// says so on a terminal is where it starts. The inset is `text::draw`'s to
/// honour as an area rather than as spaces in the string: the drawing wraps on
/// words, so leading spaces would survive the first line and vanish from every
/// one after it.
///
/// Four columns, which is `"( ) "`. Named against the mark rather than picked,
/// so a mark that changes width takes this with it.
fn indented(area: Rect, used: u16) -> Rect {
    const MARK: u16 = 4;
    let area = below(area, used);
    Rect {
        x: area.x + MARK.min(area.width),
        width: area.width.saturating_sub(MARK),
        ..area
    }
}

fn below(area: Rect, used: u16) -> Rect {
    let used = used.min(area.height);
    Rect {
        x: area.x,
        y: area.y + used,
        width: area.width,
        height: area.height - used,
    }
}

#[cfg(test)]
mod tests;

/// A chart, one line per bar.
///
/// # Why the bars lie down here
///
/// A webview draws a chart as columns standing on an axis, and a terminal has
/// one glyph per cell and a handful of rows. Standing the bars up would mean
/// drawing each one as a stack of partial blocks and giving up the labels,
/// which are the half a reader actually reads. Laid down, every bar keeps its
/// place on the axis, its magnitude and its reading, and the drawing is
/// [`meter`]'s repeated -- which is the honest answer for the same reason
/// `quasi-tui`'s timeline draws no gridlines: a terminal draws what a terminal
/// draws rather than an impression of the other renderer.
///
/// The axis is not drawn as a rule or a scale, for that same reason. It is
/// stated instead: every bar is `meter_cells` wide and full means
/// [`Chart::most`], so the widths are comparable across the run, which is the
/// one thing a chart has to get right.
///
/// # What is left out
///
/// [`Chart::label`] is not drawn. It names what the magnitudes are and every
/// bar's own [`Bar::reading`] already carries the units, so drawing it would be
/// a heading this function does not own the room for. A caller that wants it
/// says it as a heading, which is what a description does anyway.
///
/// Labels are padded to the widest, so the bars line up. That is measured in
/// characters rather than in display cells, which is wrong for a label holding
/// a wide glyph and is what [`crate::text`] would cost to bring in for a case
/// that has not turned up.
#[must_use]
pub fn chart(style: &PieceStyle, chart: &Chart<'_>, bars: &[Bar<'_>]) -> Vec<Line<'static>> {
    let widest = bars
        .iter()
        .map(|bar| bar.at.chars().count())
        .max()
        .unwrap_or(0);
    bars.iter()
        .map(|bar| chart_line(style, chart, bar, widest))
        .collect()
}

/// One bar's line: where it sits, how far it reaches, and what it says.
fn chart_line(
    style: &PieceStyle,
    chart: &Chart<'_>,
    bar: &Bar<'_>,
    widest: usize,
) -> Line<'static> {
    let cells = usize::from(style.meter_cells);
    // Rounded rather than truncated, so a bar that is nearly full does not read
    // as one cell short of every other. The multiplication is done before the
    // division for the reason it is in `meter`: in integers, the other order is
    // zero.
    let filled = if chart.most == 0 {
        0
    } else {
        let scaled = (bar.value as u128 * cells as u128).div_ceil(chart.most as u128);
        (scaled as usize).min(cells)
    };

    let mut spans = vec![Span::styled(
        format!("{:width$} ", bar.at, width = widest),
        style.secondary,
    )];
    spans.push(Span::styled(
        format!(
            "{}{}",
            style.meter_full.to_string().repeat(filled),
            style.meter_empty.to_string().repeat(cells - filled)
        ),
        style.tone(chart.tone),
    ));
    if let Some(reading) = chart_reading(bar) {
        spans.push(Span::styled(reading, style.muted));
    }
    Line::from(spans)
}

/// What a bar says beside its own drawing, or nothing.
///
/// The webview's `bar_text` in this renderer's spelling. Both facts joined the
/// same way, and both left out when the description carried neither.
fn chart_reading(bar: &Bar<'_>) -> Option<String> {
    match (bar.reading, bar.note) {
        (Some(reading), Some(note)) => Some(format!(" {reading} / {note}")),
        (Some(only), None) | (None, Some(only)) => Some(format!(" {only}")),
        (None, None) => None,
    }
}