//! Theme palette: makeover intents resolved into ratatui `Color`s, plus
//! the two Alloy-derived border tokens.
//!
//! Per docs/TOKENS.md, Alloy consumes makeover `.toml` files (the same
//! schema every make-family app already reads) and derives two extra tokens
//! locally so theme files stay minimal and cross-app compatible:
//!
//! - `border-subtle = mix(line.border, surface.page, 60%)`   decorative divider
//! - `border-strong = mix(line.border, content.primary, 65%)` focus / selection
//!
//! Mix is in linear sRGB, matching TOKENS.md's worked audit math.
//!
//! ratatui is immediate-mode with per-widget styling — there is no global
//! visuals object. Widgets in this crate take a `&Theme` at construction time
//! and pull colors from it. Apps build one `Theme` per theme load (via
//! `makeover::load_theme` + `Theme::from_theme`) and thread it through.

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

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Mode {
    Light,
    Dark,
    HighContrast,
}

#[derive(Debug, Clone, Copy)]
pub struct Theme {
    pub mode: Mode,

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

    pub line_border: Color,
    pub border_subtle: Color,
    pub border_strong: Color,

    pub category: [Color; 6],
}

#[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 {
            ThemeError::MissingKey(k) => write!(f, "theme missing required key `{k}`"),
            ThemeError::InvalidHex { key, value } => {
                write!(f, "theme key `{key}` has invalid hex value `{value}`")
            }
        }
    }
}

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

impl Theme {
    /// Resolve a loaded makeover `ThemeColors` into an Alloy `Theme`.
    /// Requires every intent Alloy renders — a malformed or partial theme is
    /// rejected explicitly rather than silently rendering with defaults.
    pub fn from_theme(theme: &ThemeColors) -> Result<Self, ThemeError> {
        let get = |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(),
            })
        };

        let surface_page = get("surface.page")?;
        let content_primary = get("content.primary")?;
        let line_border = get("line.border")?;

        let border_subtle = mix_linear_srgb(line_border, surface_page, 0.60);
        let border_strong = mix_linear_srgb(line_border, content_primary, 0.65);

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

        Ok(Self {
            mode,

            surface_page: rgb(surface_page),
            surface_raised: rgb(get("surface.raised")?),
            surface_sunken: rgb(get("surface.sunken")?),
            surface_overlay: rgb(get("surface.overlay")?),

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

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

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

            line_border: rgb(line_border),
            border_subtle: rgb(border_subtle),
            border_strong: rgb(border_strong),

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

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

/// How much color the terminal being drawn to can actually show.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ColorDepth {
    /// 24-bit. Theme colors are sent as authored.
    Full,
    /// The sixteen ANSI colors, addressed by index.
    Ansi16,
}

/// What the environment says the terminal can show.
///
/// `COLORTERM` is the only positive signal a terminal gives for 24-bit color,
/// and `TERM=linux` is the case this exists for: the Linux virtual console,
/// which is what an installer and a machine with no desktop draw on. Anything
/// else is assumed to manage 24-bit, which is the safer wrong answer. Guessing
/// [`Full`](ColorDepth::Full) on a limited terminal costs some fidelity;
/// guessing [`Ansi16`](ColorDepth::Ansi16) on a capable one throws away color
/// the user paid for.
pub fn detect_color_depth() -> ColorDepth {
    let colorterm = std::env::var("COLORTERM").unwrap_or_default();
    if colorterm == "truecolor" || colorterm == "24bit" {
        return ColorDepth::Full;
    }
    match std::env::var("TERM").unwrap_or_default().as_str() {
        "linux" | "vt100" | "vt220" | "ansi" | "dumb" => ColorDepth::Ansi16,
        _ => ColorDepth::Full,
    }
}

/// The palette entry for `c`, as an index the terminal will not reinterpret.
fn indexed(c: Color) -> Color {
    match c {
        Color::Rgb(r, g, b) => {
            Color::Indexed(makeover::quantize(Rgb { r, g, b }, &makeover::ANSI_16) as u8)
        }
        other => other,
    }
}

/// As [`indexed`], but guaranteed to stay legible against `on`.
fn indexed_against(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,
                },
                &makeover::ANSI_16,
            ) as u8)
        }
        _ => indexed(c),
    }
}

impl Theme {
    /// This theme as the terminal can actually draw it.
    ///
    /// At [`ColorDepth::Full`] the theme is returned untouched. At
    /// [`ColorDepth::Ansi16`] every color becomes a palette index, which is the
    /// point: left as 24-bit, the terminal approximates them itself, and its
    /// approximation collapses tones that the theme keeps apart. Alloy's
    /// console lost its frame that way, drawing a border in a color the Linux
    /// console could not distinguish from the page behind it.
    ///
    /// Anything that has to be seen against the page is quantized against it
    /// rather than on its own, so a border stays a border and text stays
    /// readable. The surfaces themselves are quantized plainly: they are what
    /// the others are measured against.
    #[must_use]
    pub fn for_terminal(self, depth: ColorDepth) -> Theme {
        if depth == ColorDepth::Full {
            return self;
        }

        let page = indexed(self.surface_page);
        let on_page = |c: Color| indexed_against(c, self.surface_page);

        Theme {
            mode: self.mode,

            surface_page: page,
            surface_raised: indexed(self.surface_raised),
            surface_sunken: indexed(self.surface_sunken),
            surface_overlay: indexed(self.surface_overlay),

            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_subtle: on_page(self.border_subtle),
            border_strong: on_page(self.border_strong),

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

// Linear-sRGB interpolation. Matches TOKENS.md's audit math exactly: values are
// gamma-decoded to linear light, mixed, then gamma-encoded back. Perceptually
// less uniform than OKLab but keeps the derived hex reproducible against the
// contrast tables in TOKENS.md.
fn mix_linear_srgb(a: Rgb, b: Rgb, t: f32) -> Rgb {
    let al = srgb_to_linear(a);
    let bl = srgb_to_linear(b);
    let m = (
        al.0 + (bl.0 - al.0) * t,
        al.1 + (bl.1 - al.1) * t,
        al.2 + (bl.2 - al.2) * t,
    );
    linear_to_srgb(m)
}

fn srgb_to_linear(c: Rgb) -> (f32, f32, f32) {
    (
        channel_to_linear(c.r),
        channel_to_linear(c.g),
        channel_to_linear(c.b),
    )
}

fn linear_to_srgb(c: (f32, f32, f32)) -> Rgb {
    Rgb {
        r: channel_to_srgb(c.0),
        g: channel_to_srgb(c.1),
        b: channel_to_srgb(c.2),
    }
}

fn channel_to_linear(c: u8) -> f32 {
    let c = c as f32 / 255.0;
    if c <= 0.04045 {
        c / 12.92
    } else {
        ((c + 0.055) / 1.055).powf(2.4)
    }
}

fn channel_to_srgb(c: f32) -> u8 {
    let v = if c <= 0.003_130_8 {
        c * 12.92
    } else {
        1.055 * c.powf(1.0 / 2.4) - 0.055
    };
    (v * 255.0).round().clamp(0.0, 255.0) as u8
}

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

    // TOKENS.md line 61 anchors the derivation math against Akari Dawn:
    // line.border = #cabeae, content.primary = #1a1816, mix 65% toward primary
    // must produce #7f786d (the value the contrast-audit table is calibrated on).
    // If this test fails, the audit table in TOKENS.md is stale, not the code.
    #[test]
    fn akari_dawn_border_strong_matches_tokens_md() {
        let border = Rgb::from_hex("#cabeae").unwrap();
        let primary = Rgb::from_hex("#1a1816").unwrap();
        let got = mix_linear_srgb(border, primary, 0.65);
        assert_eq!(
            (got.r, got.g, got.b),
            (0x7f, 0x78, 0x6d),
            "border-strong derivation drifted; got #{:02x}{:02x}{:02x}, expected #7f786d",
            got.r,
            got.g,
            got.b
        );
    }

    // Akari Dawn as far as this matters: the page, the text on it, and the
    // strong border derived above.
    fn akari_dawn() -> Theme {
        let page = Color::Rgb(0xe4, 0xde, 0xd6);
        Theme {
            mode: Mode::Light,
            surface_page: page,
            surface_raised: page,
            surface_sunken: page,
            surface_overlay: page,
            content_primary: Color::Rgb(0x1a, 0x18, 0x16),
            content_secondary: Color::Rgb(0x1a, 0x18, 0x16),
            content_muted: Color::Rgb(0x7f, 0x78, 0x6d),
            action_primary: Color::Rgb(0x8a, 0x45, 0x30),
            status_danger: Color::Rgb(0x8a, 0x45, 0x30),
            status_success: Color::Rgb(0x8a, 0x45, 0x30),
            status_warning: Color::Rgb(0x8a, 0x45, 0x30),
            status_info: Color::Rgb(0x8a, 0x45, 0x30),
            line_border: Color::Rgb(0xca, 0xbe, 0xae),
            border_subtle: Color::Rgb(0xda, 0xd2, 0xc7),
            border_strong: Color::Rgb(0x7f, 0x78, 0x6d),
            category: [Color::Rgb(0x8a, 0x45, 0x30); 6],
        }
    }

    #[test]
    fn a_capable_terminal_gets_the_theme_as_authored() {
        let theme = akari_dawn().for_terminal(ColorDepth::Full);
        assert_eq!(theme.border_strong, Color::Rgb(0x7f, 0x78, 0x6d));
    }

    // Indices, not RGB. Sending RGB to a terminal that cannot show it leaves
    // the approximating to the terminal, which is where the collapse happened.
    #[test]
    fn a_sixteen_color_terminal_gets_indices() {
        let theme = akari_dawn().for_terminal(ColorDepth::Ansi16);
        for color in [
            theme.surface_page,
            theme.content_primary,
            theme.border_strong,
            theme.border_subtle,
            theme.line_border,
        ] {
            assert!(matches!(color, Color::Indexed(_)), "{color:?}");
        }
    }

    // The bug, as a test: the installer's frame drew in border_strong on
    // surface_page and could not be seen.
    #[test]
    fn the_frame_stays_visible_against_the_page() {
        let theme = akari_dawn().for_terminal(ColorDepth::Ansi16);
        assert_ne!(theme.border_strong, theme.surface_page);
        assert_ne!(theme.border_subtle, theme.surface_page);
        assert_ne!(theme.content_primary, theme.surface_page);
    }
}