//! Define the colors of a theme.
use iced_core::Color;

use once_cell::sync::Lazy;
use palette::color_difference::Wcag21RelativeContrast;
use palette::rgb::Rgb;
use palette::{FromColor, Hsl, Mix};

/// A color palette.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Palette {
    /// The background [`Color`] of the [`Palette`].
    pub background: Color,
    /// The text [`Color`] of the [`Palette`].
    pub text: Color,
    /// The primary [`Color`] of the [`Palette`].
    pub primary: Color,
    /// The success [`Color`] of the [`Palette`].
    pub success: Color,
    /// The danger [`Color`] of the [`Palette`].
    pub danger: Color,
}

impl Palette {
    /// The built-in light variant of a [`Palette`].
    pub const LIGHT: Self = Self {
        background: Color::WHITE,
        text: Color::BLACK,
        primary: Color::from_rgb(
            0x5E as f32 / 255.0,
            0x7C as f32 / 255.0,
            0xE2 as f32 / 255.0,
        ),
        success: Color::from_rgb(
            0x12 as f32 / 255.0,
            0x66 as f32 / 255.0,
            0x4F as f32 / 255.0,
        ),
        danger: Color::from_rgb(
            0xC3 as f32 / 255.0,
            0x42 as f32 / 255.0,
            0x3F as f32 / 255.0,
        ),
    };

    /// The built-in dark variant of a [`Palette`].
    pub const DARK: Self = Self {
        background: Color::from_rgb(
            0x20 as f32 / 255.0,
            0x22 as f32 / 255.0,
            0x25 as f32 / 255.0,
        ),
        text: Color::from_rgb(0.90, 0.90, 0.90),
        primary: Color::from_rgb(
            0x5E as f32 / 255.0,
            0x7C as f32 / 255.0,
            0xE2 as f32 / 255.0,
        ),
        success: Color::from_rgb(
            0x12 as f32 / 255.0,
            0x66 as f32 / 255.0,
            0x4F as f32 / 255.0,
        ),
        danger: Color::from_rgb(
            0xC3 as f32 / 255.0,
            0x42 as f32 / 255.0,
            0x3F as f32 / 255.0,
        ),
    };
}

/// An extended set of colors generated from a [`Palette`].
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Extended {
    /// The set of background colors.
    pub background: Background,
    /// The set of primary colors.
    pub primary: Primary,
    /// The set of secondary colors.
    pub secondary: Secondary,
    /// The set of success colors.
    pub success: Success,
    /// The set of danger colors.
    pub danger: Danger,
    /// Whether the palette is dark or not.
    pub is_dark: bool,
}

/// The built-in light variant of an [`Extended`] palette.
pub static EXTENDED_LIGHT: Lazy<Extended> =
    Lazy::new(|| Extended::generate(Palette::LIGHT));

/// The built-in dark variant of an [`Extended`] palette.
pub static EXTENDED_DARK: Lazy<Extended> =
    Lazy::new(|| Extended::generate(Palette::DARK));

impl Extended {
    /// Generates an [`Extended`] palette from a simple [`Palette`].
    pub fn generate(palette: Palette) -> Self {
        Self {
            background: Background::new(palette.background, palette.text),
            primary: Primary::generate(
                palette.primary,
                palette.background,
                palette.text,
            ),
            secondary: Secondary::generate(palette.background, palette.text),
            success: Success::generate(
                palette.success,
                palette.background,
                palette.text,
            ),
            danger: Danger::generate(
                palette.danger,
                palette.background,
                palette.text,
            ),
            is_dark: is_dark(palette.background),
        }
    }
}

/// A pair of background and text colors.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Pair {
    /// The background color.
    pub color: Color,

    /// The text color.
    ///
    /// It's guaranteed to be readable on top of the background [`color`].
    ///
    /// [`color`]: Self::color
    pub text: Color,
}

impl Pair {
    /// Creates a new [`Pair`] from a background [`Color`] and some text [`Color`].
    pub fn new(color: Color, text: Color) -> Self {
        Self {
            color,
            text: readable(color, text),
        }
    }
}

/// A set of background colors.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Background {
    /// The base background color.
    pub base: Pair,
    /// A weaker version of the base background color.
    pub weak: Pair,
    /// A stronger version of the base background color.
    pub strong: Pair,
}

impl Background {
    /// Generates a set of [`Background`] colors from the base and text colors.
    pub fn new(base: Color, text: Color) -> Self {
        let weak = mix(base, text, 0.15);
        let strong = mix(base, text, 0.40);

        Self {
            base: Pair::new(base, text),
            weak: Pair::new(weak, text),
            strong: Pair::new(strong, text),
        }
    }
}

/// A set of primary colors.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Primary {
    /// The base primary color.
    pub base: Pair,
    /// A weaker version of the base primary color.
    pub weak: Pair,
    /// A stronger version of the base primary color.
    pub strong: Pair,
}

impl Primary {
    /// Generates a set of [`Primary`] colors from the base, background, and text colors.
    pub fn generate(base: Color, background: Color, text: Color) -> Self {
        let weak = mix(base, background, 0.4);
        let strong = deviate(base, 0.1);

        Self {
            base: Pair::new(base, text),
            weak: Pair::new(weak, text),
            strong: Pair::new(strong, text),
        }
    }
}

/// A set of secondary colors.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Secondary {
    /// The base secondary color.
    pub base: Pair,
    /// A weaker version of the base secondary color.
    pub weak: Pair,
    /// A stronger version of the base secondary color.
    pub strong: Pair,
}

impl Secondary {
    /// Generates a set of [`Secondary`] colors from the base and text colors.
    pub fn generate(base: Color, text: Color) -> Self {
        let base = mix(base, text, 0.2);
        let weak = mix(base, text, 0.1);
        let strong = mix(base, text, 0.3);

        Self {
            base: Pair::new(base, text),
            weak: Pair::new(weak, text),
            strong: Pair::new(strong, text),
        }
    }
}

/// A set of success colors.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Success {
    /// The base success color.
    pub base: Pair,
    /// A weaker version of the base success color.
    pub weak: Pair,
    /// A stronger version of the base success color.
    pub strong: Pair,
}

impl Success {
    /// Generates a set of [`Success`] colors from the base, background, and text colors.
    pub fn generate(base: Color, background: Color, text: Color) -> Self {
        let weak = mix(base, background, 0.4);
        let strong = deviate(base, 0.1);

        Self {
            base: Pair::new(base, text),
            weak: Pair::new(weak, text),
            strong: Pair::new(strong, text),
        }
    }
}

/// A set of danger colors.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Danger {
    /// The base danger color.
    pub base: Pair,
    /// A weaker version of the base danger color.
    pub weak: Pair,
    /// A stronger version of the base danger color.
    pub strong: Pair,
}

impl Danger {
    /// Generates a set of [`Danger`] colors from the base, background, and text colors.
    pub fn generate(base: Color, background: Color, text: Color) -> Self {
        let weak = mix(base, background, 0.4);
        let strong = deviate(base, 0.1);

        Self {
            base: Pair::new(base, text),
            weak: Pair::new(weak, text),
            strong: Pair::new(strong, text),
        }
    }
}

fn darken(color: Color, amount: f32) -> Color {
    let mut hsl = to_hsl(color);

    hsl.lightness = if hsl.lightness - amount < 0.0 {
        0.0
    } else {
        hsl.lightness - amount
    };

    from_hsl(hsl)
}

fn lighten(color: Color, amount: f32) -> Color {
    let mut hsl = to_hsl(color);

    hsl.lightness = if hsl.lightness + amount > 1.0 {
        1.0
    } else {
        hsl.lightness + amount
    };

    from_hsl(hsl)
}

fn deviate(color: Color, amount: f32) -> Color {
    if is_dark(color) {
        lighten(color, amount)
    } else {
        darken(color, amount)
    }
}

fn mix(a: Color, b: Color, factor: f32) -> Color {
    let a_lin = Rgb::from(a).into_linear();
    let b_lin = Rgb::from(b).into_linear();

    let mixed = a_lin.mix(b_lin, factor);
    Rgb::from_linear(mixed).into()
}

fn readable(background: Color, text: Color) -> Color {
    if is_readable(background, text) {
        text
    } else if is_dark(background) {
        Color::WHITE
    } else {
        Color::BLACK
    }
}

fn is_dark(color: Color) -> bool {
    to_hsl(color).lightness < 0.6
}

fn is_readable(a: Color, b: Color) -> bool {
    let a_srgb = Rgb::from(a);
    let b_srgb = Rgb::from(b);

    a_srgb.has_enhanced_contrast_text(b_srgb)
}

fn to_hsl(color: Color) -> Hsl {
    Hsl::from_color(Rgb::from(color))
}

fn from_hsl(hsl: Hsl) -> Color {
    Rgb::from_color(hsl).into()
}