vtcode-core 0.9.1

use anstyle::{Color, RgbColor, Style};
use anyhow::{Context, Result, anyhow};
use once_cell::sync::Lazy;
use parking_lot::RwLock;
use std::collections::HashMap;

/// Identifier for the default theme.
pub const DEFAULT_THEME_ID: &str = "ciapre-dark";

const MIN_CONTRAST: f64 = 4.5;

const WELCOME_TOOL_COLOR: RgbColor = RgbColor(0x38, 0x3B, 0x73);

/// Palette describing UI colors for the terminal experience.
#[derive(Clone, Debug)]
pub struct ThemePalette {
    pub primary_accent: RgbColor,
    pub background: RgbColor,
    pub foreground: RgbColor,
    pub secondary_accent: RgbColor,
    pub alert: RgbColor,
}

impl ThemePalette {
    fn style_from(color: RgbColor, bold: bool) -> Style {
        let mut style = Style::new().fg_color(Some(Color::Rgb(color)));
        if bold {
            style = style.bold();
        }
        style
    }

    fn build_styles(&self) -> ThemeStyles {
        let primary = self.primary_accent;
        let background = self.background;
        let secondary = self.secondary_accent;

        let fallback_light = RgbColor(0xFF, 0xFF, 0xFF);

        let text_color = ensure_contrast(
            self.foreground,
            background,
            MIN_CONTRAST,
            &[
                lighten(self.foreground, 0.25),
                lighten(secondary, 0.2),
                fallback_light,
            ],
        );
        let info_color = ensure_contrast(
            secondary,
            background,
            MIN_CONTRAST,
            &[lighten(secondary, 0.2), text_color, fallback_light],
        );
        let tool_color = WELCOME_TOOL_COLOR;
        let response_color = ensure_contrast(
            text_color,
            background,
            MIN_CONTRAST,
            &[lighten(text_color, 0.15), fallback_light],
        );
        let user_color = ensure_contrast(
            lighten(primary, 0.25),
            background,
            MIN_CONTRAST,
            &[lighten(secondary, 0.15), info_color, text_color],
        );
        let alert_color = ensure_contrast(
            self.alert,
            background,
            MIN_CONTRAST,
            &[lighten(self.alert, 0.2), fallback_light, text_color],
        );

        ThemeStyles {
            info: Self::style_from(info_color, true),
            error: Self::style_from(alert_color, true),
            output: Self::style_from(text_color, false),
            response: Self::style_from(response_color, false),
            tool: Style::new().fg_color(Some(Color::Rgb(tool_color))).bold(),
            user: Self::style_from(user_color, false),
            primary: Self::style_from(primary, false),
            secondary: Self::style_from(secondary, false),
            background: Color::Rgb(background),
            foreground: Color::Rgb(text_color),
        }
    }
}

/// Styles computed from palette colors.
#[derive(Clone, Debug)]
pub struct ThemeStyles {
    pub info: Style,
    pub error: Style,
    pub output: Style,
    pub response: Style,
    pub tool: Style,
    pub user: Style,
    pub primary: Style,
    pub secondary: Style,
    pub background: Color,
    pub foreground: Color,
}

#[derive(Clone, Debug)]
pub struct ThemeDefinition {
    pub id: &'static str,
    pub label: &'static str,
    pub palette: ThemePalette,
}

#[derive(Clone, Debug)]
struct ActiveTheme {
    id: String,
    label: String,
    palette: ThemePalette,
    styles: ThemeStyles,
}

static REGISTRY: Lazy<HashMap<&'static str, ThemeDefinition>> = Lazy::new(|| {
    let mut map = HashMap::new();
    map.insert(
        "ciapre-dark",
        ThemeDefinition {
            id: "ciapre-dark",
            label: "Ciapre Dark",
            palette: ThemePalette {
                primary_accent: RgbColor(0xBF, 0xB3, 0x8F),
                background: RgbColor(0x26, 0x26, 0x26),
                foreground: RgbColor(0xBF, 0xB3, 0x8F),
                secondary_accent: RgbColor(0xD9, 0x9A, 0x4E),
                alert: RgbColor(0xFF, 0x8A, 0x8A),
            },
        },
    );
    map.insert(
        "ciapre-blue",
        ThemeDefinition {
            id: "ciapre-blue",
            label: "Ciapre Blue",
            palette: ThemePalette {
                primary_accent: RgbColor(0xBF, 0xB3, 0x8F),
                background: RgbColor(0x38, 0x3B, 0x73),
                foreground: RgbColor(0xBF, 0xB3, 0x8F),
                secondary_accent: RgbColor(0xBF, 0xB3, 0x8F),
                alert: RgbColor(0xFF, 0x8A, 0x8A),
            },
        },
    );
    map
});

static ACTIVE: Lazy<RwLock<ActiveTheme>> = Lazy::new(|| {
    let default = REGISTRY
        .get(DEFAULT_THEME_ID)
        .expect("default theme must exist");
    let styles = default.palette.build_styles();
    RwLock::new(ActiveTheme {
        id: default.id.to_string(),
        label: default.label.to_string(),
        palette: default.palette.clone(),
        styles,
    })
});

/// Set the active theme by identifier.
pub fn set_active_theme(theme_id: &str) -> Result<()> {
    let id_lc = theme_id.trim().to_lowercase();
    let theme = REGISTRY
        .get(id_lc.as_str())
        .ok_or_else(|| anyhow!("Unknown theme '{theme_id}'"))?;

    let styles = theme.palette.build_styles();
    let mut guard = ACTIVE.write();
    guard.id = theme.id.to_string();
    guard.label = theme.label.to_string();
    guard.palette = theme.palette.clone();
    guard.styles = styles;
    Ok(())
}

/// Get the identifier of the active theme.
pub fn active_theme_id() -> String {
    ACTIVE.read().id.clone()
}

/// Get the human-readable label of the active theme.
pub fn active_theme_label() -> String {
    ACTIVE.read().label.clone()
}

/// Get the current styles cloned from the active theme.
pub fn active_styles() -> ThemeStyles {
    ACTIVE.read().styles.clone()
}

/// Slightly darkened accent color for banner-like copy.
pub fn banner_color() -> RgbColor {
    WELCOME_TOOL_COLOR
}

/// Slightly darkened accent style for banner-like copy.
pub fn banner_style() -> Style {
    Style::new()
        .fg_color(Some(Color::Rgb(WELCOME_TOOL_COLOR)))
        .bold()
}

/// Enumerate available theme identifiers.
pub fn available_themes() -> Vec<&'static str> {
    let mut keys: Vec<_> = REGISTRY.keys().copied().collect();
    keys.sort();
    keys
}

/// Look up a theme label for display.
pub fn theme_label(theme_id: &str) -> Option<&'static str> {
    REGISTRY.get(theme_id).map(|definition| definition.label)
}

fn relative_luminance(color: RgbColor) -> f64 {
    fn channel(value: u8) -> f64 {
        let c = (value as f64) / 255.0;
        if c <= 0.03928 {
            c / 12.92
        } else {
            ((c + 0.055) / 1.055).powf(2.4)
        }
    }
    let r = channel(color.0);
    let g = channel(color.1);
    let b = channel(color.2);
    0.2126 * r + 0.7152 * g + 0.0722 * b
}

fn contrast_ratio(foreground: RgbColor, background: RgbColor) -> f64 {
    let fg = relative_luminance(foreground);
    let bg = relative_luminance(background);
    let (lighter, darker) = if fg > bg { (fg, bg) } else { (bg, fg) };
    (lighter + 0.05) / (darker + 0.05)
}

fn ensure_contrast(
    candidate: RgbColor,
    background: RgbColor,
    min_ratio: f64,
    fallbacks: &[RgbColor],
) -> RgbColor {
    if contrast_ratio(candidate, background) >= min_ratio {
        return candidate;
    }
    for &fallback in fallbacks {
        if contrast_ratio(fallback, background) >= min_ratio {
            return fallback;
        }
    }
    candidate
}

fn mix(color: RgbColor, target: RgbColor, ratio: f64) -> RgbColor {
    let ratio = ratio.clamp(0.0, 1.0);
    let blend = |c: u8, t: u8| -> u8 {
        let c = c as f64;
        let t = t as f64;
        ((c + (t - c) * ratio).round()).clamp(0.0, 255.0) as u8
    };
    RgbColor(
        blend(color.0, target.0),
        blend(color.1, target.1),
        blend(color.2, target.2),
    )
}

fn lighten(color: RgbColor, ratio: f64) -> RgbColor {
    mix(color, RgbColor(0xFF, 0xFF, 0xFF), ratio)
}

/// Resolve a theme identifier from configuration or CLI input.
pub fn resolve_theme(preferred: Option<String>) -> String {
    preferred
        .and_then(|candidate| {
            let trimmed = candidate.trim().to_lowercase();
            if trimmed.is_empty() {
                None
            } else if REGISTRY.contains_key(trimmed.as_str()) {
                Some(trimmed)
            } else {
                None
            }
        })
        .unwrap_or_else(|| DEFAULT_THEME_ID.to_string())
}

/// Validate a theme and return its label for messaging.
pub fn ensure_theme(theme_id: &str) -> Result<&'static str> {
    REGISTRY
        .get(theme_id)
        .map(|definition| definition.label)
        .context("Theme not found")
}