//! The theme engine: reads the running system theme, resolves it through
//! presets and overrides, and installs the tokens every component paints
//! from.
//!
//! Pipeline (plan §4.5): `ThemeSource` snapshot → `resolve` overlay chain →
//! `Theme` global → all windows repaint. Watchers re-run the pipeline on
//! real OS change events.

mod colors;
mod definition;
mod presets;
mod ramps;
mod resolve;
mod source;
mod system;

pub use colors::ColorTokens;
pub use definition::ThemeDefinition;
pub use ramps::{AccentShades, Oklch};
pub use resolve::{Ramps, ResolvedTheme};
pub use system::{AccessibilityPreferences, PartialPalette, SourceKind, SystemTheme};

use gpui::{App, Global, Pixels, WindowAppearance, px};

/// Light or dark, resolved from the system appearance.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, serde::Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum ThemeVariant {
    #[default]
    Light,
    Dark,
}

impl ThemeVariant {
    fn from_appearance(appearance: WindowAppearance) -> Self {
        match appearance {
            WindowAppearance::Light | WindowAppearance::VibrantLight => Self::Light,
            WindowAppearance::Dark | WindowAppearance::VibrantDark => Self::Dark,
        }
    }
}

/// The resolved theme, installed as the app-wide global.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Theme {
    pub variant: ThemeVariant,
    pub colors: ColorTokens,
    pub ramps: Ramps,
    pub radius: Radius,
    pub accessibility: AccessibilityPreferences,
}

impl Global for Theme {}

/// Corner radii components paint from; grows one class at a time.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Radius {
    /// Small controls: checkbox and radio indicators.
    pub sm: Pixels,
    pub control: Pixels,
    /// Pill and circle shapes.
    pub full: Pixels,
}

impl Default for Radius {
    fn default() -> Self {
        Self {
            sm: px(4.),
            control: px(6.),
            full: px(9999.),
        }
    }
}

/// Reads the resolved theme global from any app context.
pub trait ActiveTheme {
    fn theme(&self) -> &Theme;
}

impl ActiveTheme for App {
    fn theme(&self) -> &Theme {
        Theme::global(self)
    }
}

impl Theme {
    /// Reads the theme global. Panics before `init`.
    pub fn global(cx: &App) -> &Self {
        cx.global::<Self>()
    }

    fn from_resolved(resolved: ResolvedTheme) -> Self {
        Self {
            variant: resolved.variant,
            colors: resolved.colors,
            ramps: resolved.ramps,
            radius: resolved.radius,
            accessibility: resolved.accessibility,
        }
    }

    /// Installs the engine global, its platform watchers, and the initial resolved theme.
    pub fn init(cx: &mut App) {
        let mut engine = ThemeEngine {
            source: source::platform_source(),
            mode_override: None,
            preset: None,
        };
        engine.source.install_watchers(cx.to_async());
        cx.set_global(engine);
        reapply(cx);
    }

    /// Re-resolves when a window's appearance differs from the resolved variant.
    ///
    /// Wire to `Window::observe_window_appearance`.
    pub fn sync_from_window(window: &gpui::Window, cx: &mut App) {
        let variant = ThemeVariant::from_appearance(window.appearance());
        if cx.global::<Theme>().variant != variant
            || cx.global::<ThemeEngine>().mode_override.is_none()
        {
            reapply(cx);
        }
    }
}

/// The engine's knobs and its platform source.
struct ThemeEngine {
    source: Box<dyn source::ThemeSource>,
    mode_override: Option<ThemeVariant>,
    preset: Option<(&'static str, ThemeDefinition)>,
}

impl Global for ThemeEngine {}

/// Reads the system, resolves through the current knobs,
/// installs the theme global, and repaints every window.
pub(crate) fn reapply(cx: &mut App) {
    let (system_appearance, preset, mode_override) = {
        let engine = cx.global::<ThemeEngine>();
        (
            ThemeVariant::from_appearance(cx.window_appearance()),
            engine.preset.as_ref().map(|(_, def)| def.clone()),
            engine.mode_override,
        )
    };

    let variant = mode_override
        .or(preset.as_ref().and_then(|def| def.mode))
        .unwrap_or(system_appearance);

    let system = cx.global::<ThemeEngine>().source.snapshot(variant);
    let resolved = resolve::resolve(&system, preset.as_ref(), mode_override);

    cx.set_global(Theme::from_resolved(resolved));
    cx.refresh_windows();
}

/// Forces a variant, independent of the OS. `None` follows the system.
pub fn set_mode_override(variant: Option<ThemeVariant>, cx: &mut App) {
    cx.global_mut::<ThemeEngine>().mode_override = variant;
    reapply(cx);
}

/// Installs a built-in preset, or `None` to follow the system again.
pub fn set_preset(name: Option<&str>, cx: &mut App) -> anyhow::Result<()> {
    let preset = match name {
        Some(name) => {
            let def =
                presets::builtin(name).ok_or_else(|| anyhow::anyhow!("unknown preset: {name}"))?;
            let static_name = presets::preset_names()
                .iter()
                .copied()
                .find(|candidate| *candidate == name)
                .ok_or_else(|| anyhow::anyhow!("unknown preset: {name}"))?;
            Some((static_name, def))
        }
        None => None,
    };
    cx.global_mut::<ThemeEngine>().preset = preset;
    reapply(cx);
    Ok(())
}

/// The variant the mode override forces, if any.
pub fn mode_override(cx: &App) -> Option<ThemeVariant> {
    cx.global::<ThemeEngine>().mode_override
}

/// The active preset name, if one is installed.
pub fn active_preset(cx: &App) -> Option<&'static str> {
    cx.global::<ThemeEngine>()
        .preset
        .as_ref()
        .map(|(name, _)| *name)
}

/// Clears the mode override and preset; the theme follows the system again.
pub fn follow_system(cx: &mut App) {
    let engine = cx.global_mut::<ThemeEngine>();
    engine.mode_override = None;
    engine.preset = None;
    reapply(cx);
}

/// Which adapter produced the current system snapshot.
pub fn detected_source(cx: &App) -> &'static str {
    cx.global::<ThemeEngine>().source.label()
}