makeover-tui 0.7.0

//! A loaded makeover theme, resolved into the colours ratatui draws with.
//!
//! Behind the `theme` feature, because it is the one thing here that needs
//! `makeover` itself. The rest of this crate takes [`Color`]s it is handed and
//! never asks where they came from, which keeps a consumer that only wants
//! [`frame`](crate::frame) off the theme loader and its embedded theme files.
//!
//! # Why this lives here rather than in each consumer
//!
//! Reading makeover's intents into ratatui `Color`s is the same work every
//! terminal consumer does, and doing it twice is how two of them end up
//! disagreeing about which intent a surface reads from. The mapping is
//! mechanical, the failure mode is silent, and there is exactly one right
//! answer, so it belongs with the renderer.
//!
//! # What is deliberately absent
//!
//! Tokens a consumer derives for itself. `alloy_tui` mixes a `border-subtle`
//! and its own focus-ring `border-strong` out of the authored border, holding
//! the latter to WCAG AA-UI against the page because Alloy spends it as the
//! entire focus cue. makeover emits a `border-strong` too, and it is a flat 5%
//! darkening: a firmer divider, not a focus ring. Those are different tokens
//! wearing one name, and on Akari Dawn they land at 1.63:1 and 3.27:1. This
//! struct carries makeover's, and a consumer that needs its own keeps deriving
//! it. Adopting one for the other would take a focus ring to half its floor.

use makeover::{Rgb, ThemeColors};
use ratatui::style::Color;

/// A theme's polarity, as its author declared it.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Mode {
    Light,
    Dark,
    HighContrast,
}

/// A makeover theme's intents, resolved to ratatui colours.
///
/// `#[non_exhaustive]`: this gains a field whenever makeover gains an intent,
/// and without the attribute every one of those would be a major here. Nothing
/// should be building one field-by-field anyway, since [`Theme::from_theme`] is
/// the only way to get one and a partial theme is an error rather than a
/// default.
#[derive(Debug, Clone, Copy)]
#[non_exhaustive]
pub struct Theme {
    pub mode: Mode,

    pub surface_page: Color,
    pub surface_raised: Color,
    pub surface_sunken: Color,
    pub surface_overlay: Color,

    /// makeover's inset content surface: the surface inside a raised container,
    /// so a list reads as content in a container rather than as bands on a
    /// panel.
    ///
    /// Not [`surface_sunken`](Theme::surface_sunken). A theme is free to author
    /// sunken *darker* than raised while a well always inverts away from the
    /// text, so substituting one for the other lands a well on the wrong side of
    /// its face on exactly the themes where it matters.
    ///
    /// `None` where makeover derived nothing, which is a theme authoring no
    /// raised surface or no content colour. Left missing rather than guessed,
    /// the same way [`Palette::fill`](crate::Palette::fill) answers a missing
    /// well with structure instead of a substitute colour.
    pub surface_well: Option<Color>,

    pub content_primary: Color,
    pub content_secondary: Color,
    pub content_muted: Color,

    pub action_primary: Color,

    pub status_danger: Color,
    pub status_success: Color,
    pub status_warning: Color,
    pub status_info: Color,

    /// The authored border colour.
    pub line_border: Color,
    /// makeover's derived firmer divider: the authored border, 5% darker.
    ///
    /// A divider, not a focus ring. See the module header before spending it as
    /// one.
    pub border_strong: Color,

    /// The lit and shadowed edges of a raised surface.
    ///
    /// A control is lit from the top left, so its top and left edges take
    /// `bevel_light` and its bottom and right edges `bevel_dark`; swapping the
    /// two recesses it, which is what a pressed state and a text well are. The
    /// light source does not flip with polarity, or the rule stops transferring
    /// between widgets, which is the whole reason to have one.
    pub bevel_light: Color,
    pub bevel_dark: Color,

    pub category: [Color; 6],
}

/// Why a theme could not be resolved.
///
/// Both variants name the key, because "the theme is bad" is not something a
/// user can act on and "the theme is missing `content.muted`" is.
#[derive(Debug, Clone)]
pub enum ThemeError {
    MissingKey(&'static str),
    InvalidHex { key: &'static str, value: String },
}

impl std::fmt::Display for ThemeError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::MissingKey(k) => write!(f, "theme missing required key `{k}`"),
            Self::InvalidHex { key, value } => {
                write!(f, "theme key `{key}` has invalid hex value `{value}`")
            }
        }
    }
}

impl std::error::Error for ThemeError {}

impl Theme {
    /// Resolve a loaded [`ThemeColors`] into the colours ratatui draws with.
    ///
    /// Every intent this struct names is required, apart from
    /// [`surface_well`](Theme::surface_well), which makeover derives only when
    /// the theme gave it enough to derive from. A malformed or partial theme is
    /// rejected rather than papered over with defaults: rendering in colours
    /// that appear nowhere in the theme file is worse than refusing to render.
    pub fn from_theme(theme: &ThemeColors) -> Result<Self, ThemeError> {
        let authored = |key: &'static str| -> Result<Rgb, ThemeError> {
            let hex = theme.colors.get(key).ok_or(ThemeError::MissingKey(key))?;
            Rgb::from_hex(hex).ok_or_else(|| ThemeError::InvalidHex {
                key,
                value: hex.clone(),
            })
        };

        // The bevel pair, the well and the firm border are makeover's derived
        // intents, so a console, a webview and an egui app light a raised
        // surface the same way. Read through `resolve` rather than recomputed
        // here, which is the point of them living in that crate.
        let resolved = makeover::resolve(theme);
        let derived = |key: &'static str| -> Result<Rgb, ThemeError> {
            let hex = resolved.hex(key).ok_or(ThemeError::MissingKey(key))?;
            Rgb::from_hex(hex).ok_or_else(|| ThemeError::InvalidHex {
                key,
                value: hex.to_string(),
            })
        };

        let mode = match theme.meta.variant.as_str() {
            "dark" => Mode::Dark,
            "high-contrast" => Mode::HighContrast,
            _ => Mode::Light,
        };

        Ok(Self {
            mode,

            surface_page: rgb(authored("surface.page")?),
            surface_raised: rgb(authored("surface.raised")?),
            surface_sunken: rgb(authored("surface.sunken")?),
            surface_overlay: rgb(authored("surface.overlay")?),
            surface_well: resolved
                .hex("surface-well")
                .and_then(Rgb::from_hex)
                .map(rgb),

            content_primary: rgb(authored("content.primary")?),
            content_secondary: rgb(authored("content.secondary")?),
            content_muted: rgb(authored("content.muted")?),

            action_primary: rgb(authored("action.primary")?),

            status_danger: rgb(authored("status.danger")?),
            status_success: rgb(authored("status.success")?),
            status_warning: rgb(authored("status.warning")?),
            status_info: rgb(authored("status.info")?),

            line_border: rgb(authored("line.border")?),
            border_strong: rgb(derived("border-strong")?),

            bevel_light: rgb(derived("bevel-light")?),
            bevel_dark: rgb(derived("bevel-dark")?),

            category: [
                rgb(authored("category.one")?),
                rgb(authored("category.two")?),
                rgb(authored("category.three")?),
                rgb(authored("category.four")?),
                rgb(authored("category.five")?),
                rgb(authored("category.six")?),
            ],
        })
    }

    /// This theme as the terminal can actually draw it.
    ///
    /// At [`TrueColor`](crate::Fidelity::TrueColor) the theme is returned
    /// untouched. Otherwise every colour becomes a palette index, which is the
    /// point: left as 24-bit, the terminal approximates them itself, and its
    /// approximation collapses tones the theme keeps apart. Alloy's console lost
    /// its frame that way, drawing a border in a colour the Linux console could
    /// not tell from the page behind it.
    ///
    /// Anything that has to be seen against the page is quantised against it
    /// rather than on its own, so a border stays a border and text stays
    /// readable. The surfaces themselves are quantised plainly: they are what
    /// the others are measured against.
    ///
    /// The bevel edges are quantised plainly too, for a different reason. They
    /// are measured against the raised surface they surround rather than against
    /// the page, and running them through [`Quantize::against`] would push both
    /// onto the same entry and invert the bevel on one side. At
    /// [`Ansi16`](crate::Fidelity::Ansi16) the palette cannot hold the pair at
    /// all and one edge lands back on its face, which is a property of sixteen
    /// colours rather than something this can fix. A caller drawing there does
    /// not have to handle it: [`Theme::palette`] carries the fidelity through,
    /// and [`frame`](crate::frame) answers it with glyphs instead of tones.
    ///
    /// A consumer holding tokens of its own quantises them alongside this, with
    /// the same [`Quantize`], rather than after the fact.
    #[must_use]
    pub fn for_terminal(self, fidelity: crate::Fidelity) -> Self {
        let Some(q) = Quantize::for_fidelity(fidelity) else {
            return self;
        };

        let plain = |c: Color| q.plain(c);
        let on_page = |c: Color| q.against(c, self.surface_page);

        Self {
            mode: self.mode,

            surface_page: plain(self.surface_page),
            surface_raised: plain(self.surface_raised),
            surface_sunken: plain(self.surface_sunken),
            surface_overlay: plain(self.surface_overlay),
            // Plainly, like the other surfaces and for the same reason as the
            // bevel pair: a well is measured against the raised face it is cut
            // into, not against the page, so quantising it against the page
            // would push it toward contrast it is not supposed to have.
            surface_well: self.surface_well.map(plain),

            content_primary: on_page(self.content_primary),
            content_secondary: on_page(self.content_secondary),
            content_muted: on_page(self.content_muted),

            action_primary: on_page(self.action_primary),

            status_danger: on_page(self.status_danger),
            status_success: on_page(self.status_success),
            status_warning: on_page(self.status_warning),
            status_info: on_page(self.status_info),

            line_border: on_page(self.line_border),
            border_strong: on_page(self.border_strong),

            bevel_light: plain(self.bevel_light),
            bevel_dark: plain(self.bevel_dark),

            category: self.category.map(on_page),
        }
    }

    /// The depth-painting palette this theme implies, at `fidelity`.
    ///
    /// The bridge between the two halves of this crate: [`Theme`] is what a
    /// theme file says, [`Palette`](crate::Palette) is the subset
    /// [`frame`](crate::frame) and [`paint_bevel`](crate::paint_bevel) need. A
    /// consumer holding a `Theme` should not be assembling that by hand and
    /// picking the wrong surface for the well.
    #[must_use]
    pub const fn palette(&self, fidelity: crate::Fidelity) -> crate::Palette {
        crate::Palette {
            page: self.surface_page,
            raised: self.surface_raised,
            overlay: self.surface_overlay,
            well: self.surface_well,
            bevel_light: self.bevel_light,
            bevel_dark: self.bevel_dark,
            fidelity,
        }
    }
}

fn rgb(c: Rgb) -> Color {
    Color::Rgb(c.r, c.g, c.b)
}

/// The palette a [`Fidelity`](crate::Fidelity) quantises into, and the rules for
/// landing a colour in it.
///
/// Public because a consumer carrying tokens of its own has to quantise them the
/// same way this crate quantises the ones it knows about. `alloy_tui` derives a
/// decorative divider and a focus ring from the authored border; those are its
/// tokens, but "a colour that must stay legible against the page is quantised
/// against the page" is not its rule to reinvent.
#[derive(Debug, Clone, Copy)]
pub struct Quantize {
    palette: &'static [Rgb],
    offset: usize,
}

impl Quantize {
    /// The quantiser for `fidelity`, or `None` at
    /// [`TrueColor`](crate::Fidelity::TrueColor), where nothing is quantised.
    ///
    /// 256 resolves to makeover's fixed region rather than the whole table: the
    /// low sixteen are repaintable in every emulator, so a match landing there
    /// is a match against a colour the user may have moved out from under it.
    #[must_use]
    pub const fn for_fidelity(fidelity: crate::Fidelity) -> Option<Self> {
        match fidelity {
            crate::Fidelity::TrueColor => None,
            crate::Fidelity::Ansi256 => Some(Self {
                palette: makeover::ANSI_240,
                offset: makeover::ANSI_240_OFFSET,
            }),
            crate::Fidelity::Ansi16 => Some(Self {
                palette: &makeover::ANSI_16,
                offset: 0,
            }),
        }
    }

    /// The palette entry for `c`, as an index the terminal will not reinterpret.
    ///
    /// For a colour measured against the surface it sits on rather than against
    /// the page: the surfaces themselves, and the bevel pair.
    #[must_use]
    pub fn plain(&self, c: Color) -> Color {
        match c {
            Color::Rgb(r, g, b) => Color::Indexed(
                (makeover::quantize(Rgb { r, g, b }, self.palette) + self.offset) as u8,
            ),
            other => other,
        }
    }

    /// As [`plain`](Self::plain), but guaranteed to stay legible against `on`.
    ///
    /// Only for a colour whose job is to be told apart from a known background.
    /// It answers "nearest entry that still contrasts with `on`" and has no
    /// notion of which side of `on` the answer should fall, so a pair of colours
    /// that must also stay apart from *each other* is the one thing it must not
    /// be used for: both get pushed onto the same contrasting entry. That is why
    /// the bevel edges go through [`plain`](Self::plain).
    #[must_use]
    pub fn against(&self, c: Color, on: Color) -> Color {
        match (c, on) {
            (Color::Rgb(r, g, b), Color::Rgb(br, bg, bb)) => Color::Indexed(
                (makeover::quantize_against(
                    Rgb { r, g, b },
                    Rgb {
                        r: br,
                        g: bg,
                        b: bb,
                    },
                    self.palette,
                ) + self.offset) as u8,
            ),
            _ => self.plain(c),
        }
    }
}

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

    fn bundled(id: &str) -> ThemeColors {
        let dir = makeover::bundled_themes_dir().expect("makeover ships themes");
        makeover::load_theme(&[(dir, false)], id).expect("bundled theme loads")
    }

    #[test]
    fn every_bundled_theme_resolves() {
        // The point of rejecting a partial theme is that it never happens to a
        // theme we ship. If one of these stops resolving, that is a real gap in
        // the theme file, not a reason to soften the error.
        let dir = makeover::bundled_themes_dir().expect("makeover ships themes");
        let metas = makeover::list_themes_from_dirs(&[(dir, false)]);
        assert!(
            !metas.is_empty(),
            "makeover shipped no themes to test against"
        );
        for meta in &metas {
            let colors = bundled(&meta.id);
            assert!(
                Theme::from_theme(&colors).is_ok(),
                "bundled theme `{}` failed to resolve",
                meta.id
            );
        }
    }

    #[test]
    fn a_missing_intent_names_the_key_it_wanted() {
        let mut colors = bundled("goingson");
        colors.colors.remove("content.muted");
        match Theme::from_theme(&colors) {
            Err(ThemeError::MissingKey(k)) => assert_eq!(k, "content.muted"),
            other => panic!("expected MissingKey(content.muted), got {other:?}"),
        }
    }

    #[test]
    fn an_unparseable_hex_names_the_key_and_the_value() {
        let mut colors = bundled("goingson");
        colors
            .colors
            .insert("content.muted".into(), "not-a-colour".into());
        match Theme::from_theme(&colors) {
            Err(ThemeError::InvalidHex { key, value }) => {
                assert_eq!(key, "content.muted");
                assert_eq!(value, "not-a-colour");
            }
            other => panic!("expected InvalidHex, got {other:?}"),
        }
    }

    #[test]
    fn a_capable_terminal_gets_the_theme_as_authored() {
        let theme = Theme::from_theme(&bundled("goingson")).expect("resolves");
        let same = theme.for_terminal(crate::Fidelity::TrueColor);
        assert_eq!(same.surface_page, theme.surface_page);
        assert_eq!(same.content_primary, theme.content_primary);
        assert!(matches!(same.surface_page, Color::Rgb(..)));
    }

    #[test]
    fn a_limited_terminal_gets_indices_rather_than_rgb() {
        let theme = Theme::from_theme(&bundled("goingson")).expect("resolves");
        for fidelity in [crate::Fidelity::Ansi16, crate::Fidelity::Ansi256] {
            let q = theme.for_terminal(fidelity);
            assert!(
                matches!(q.surface_page, Color::Indexed(_)),
                "{fidelity:?} left a surface as rgb"
            );
            assert!(
                matches!(q.content_primary, Color::Indexed(_)),
                "{fidelity:?} left content as rgb"
            );
        }
    }

    #[test]
    fn the_256_indices_land_outside_the_repaintable_low_sixteen() {
        // The reason Quantize::for_fidelity resolves 256 to makeover's fixed
        // region: an index below 16 is one the user's emulator may have moved.
        let theme = Theme::from_theme(&bundled("goingson")).expect("resolves");
        let q = theme.for_terminal(crate::Fidelity::Ansi256);
        for (name, c) in [
            ("surface_page", q.surface_page),
            ("content_primary", q.content_primary),
            ("bevel_light", q.bevel_light),
            ("bevel_dark", q.bevel_dark),
        ] {
            match c {
                Color::Indexed(i) => assert!(i >= 16, "{name} landed on repaintable index {i}"),
                other => panic!("{name} was not quantised: {other:?}"),
            }
        }
    }

    #[test]
    fn the_bevel_pair_stays_two_tones_at_256() {
        // Quantised plainly rather than against the page, precisely so they do
        // not collapse onto one entry and invert the bevel on one side.
        let theme = Theme::from_theme(&bundled("goingson")).expect("resolves");
        let q = theme.for_terminal(crate::Fidelity::Ansi256);
        assert_ne!(q.bevel_light, q.bevel_dark);
    }

    #[test]
    fn the_palette_takes_the_well_and_not_the_sunken_surface() {
        // The substitution this crate deleted from the description, asserted
        // absent here too: a theme authoring sunken darker than raised would
        // land the well on the wrong side of its face.
        let colors = bundled("goingson");
        let theme = Theme::from_theme(&colors).expect("resolves");
        let palette = theme.palette(crate::Fidelity::TrueColor);
        assert_eq!(palette.well, theme.surface_well);
        assert_ne!(palette.well, Some(theme.surface_sunken));
    }
}