use crate::{composite::over, steps::steps, Component, Theme};
use palette::{rgb::Rgba, Darken, IntoColor, Lighten, Srgba};
use std::{fs::File, io::prelude::*, num::NonZeroUsize};
use thiserror::Error;

#[derive(Error, Debug)]
pub enum OutputError {
    #[error("IO Error: {0}")]
    Io(std::io::Error),
    #[error("Missing config directory")]
    MissingConfigDir,
}

impl Theme {
    /// turn the theme into css
    pub fn as_gtk4(&self) -> String {
        let Self {
            background,
            primary,
            secondary,
            accent,
            destructive,
            warning,
            success,
            palette,
            ..
        } = self;

        let window_bg = to_hex(background.base);
        let window_fg = to_hex(background.on);

        let view_bg = to_hex(primary.base);
        let view_fg = to_hex(primary.on);

        let headerbar_bg = to_hex(background.base);
        let headerbar_fg = to_hex(background.on);
        let headerbar_border_color = to_hex(background.divider);

        let sidebar_bg = to_hex(primary.base);
        let sidebar_fg = to_hex(primary.on);
        let sidebar_shade = to_hex(if self.is_dark {
            Rgba::new(0.0, 0.0, 0.0, 0.08)
        } else {
            Rgba::new(0.0, 0.0, 0.0, 0.32)
        });
        let backdrop_overlay = Srgba::new(1.0, 1.0, 1.0, if self.is_dark { 0.08 } else { 0.32 });
        let sidebar_backdrop = to_hex(over(backdrop_overlay, primary.base));

        let secondary_sidebar_bg = to_hex(secondary.base);
        let secondary_sidebar_fg = to_hex(secondary.on);
        let secondary_sidebar_shade = to_hex(if self.is_dark {
            Rgba::new(0.0, 0.0, 0.0, 0.08)
        } else {
            Rgba::new(0.0, 0.0, 0.0, 0.32)
        });
        let secondary_sidebar_backdrop = to_hex(over(backdrop_overlay, secondary.base));

        let headerbar_backdrop = to_hex(background.base);

        let card_bg = to_hex(background.component.base);
        let card_fg = to_hex(background.component.on);

        let thumbnail_bg = to_hex(background.component.base);
        let thumbnail_fg = to_hex(background.component.on);

        let dialog_bg = to_hex(primary.base);
        let dialog_fg = to_hex(primary.on);

        let popover_bg = to_hex(background.component.base);
        let popover_fg = to_hex(background.component.on);

        let shade = to_hex(if self.is_dark {
            Rgba::new(0.0, 0.0, 0.0, 0.32)
        } else {
            Rgba::new(0.0, 0.0, 0.0, 0.08)
        });

        let mut inverted_bg_divider = background.base;
        inverted_bg_divider.alpha = 0.5;
        let scrollbar_outline = to_hex(inverted_bg_divider);

        let mut css = format! {r#"
@define-color window_bg_color #{window_bg};
@define-color window_fg_color #{window_fg};

@define-color view_bg_color #{view_bg};
@define-color view_fg_color #{view_fg};

@define-color headerbar_bg_color #{headerbar_bg};
@define-color headerbar_fg_color #{headerbar_fg};
@define-color headerbar_border_color_color #{headerbar_border_color};
@define-color headerbar_backdrop_color #{headerbar_backdrop};

@define-color sidebar_bg_color #{sidebar_bg};
@define-color sidebar_fg_color #{sidebar_fg};
@define-color sidebar_shade_color #{sidebar_shade};
@define-color sidebar_backdrop_color #{sidebar_backdrop};

@define-color secondary_sidebar_bg_color #{secondary_sidebar_bg};
@define-color secondary_sidebar_fg_color #{secondary_sidebar_fg};
@define-color secondary_sidebar_shade_color #{secondary_sidebar_shade};
@define-color secondary_sidebar_backdrop_color #{secondary_sidebar_backdrop};

@define-color card_bg_color #{card_bg};
@define-color card_fg_color #{card_fg};

@define-color thumbnail_bg_color #{thumbnail_bg};
@define-color thumbnail_fg_color #{thumbnail_fg};

@define-color dialog_bg_color #{dialog_bg};
@define-color dialog_fg_color #{dialog_fg};

@define-color popover_bg_color #{popover_bg};
@define-color popover_fg_color #{popover_fg};

@define-color shade_color #{shade};
@define-color scrollbar_outline_color #{scrollbar_outline};
"#};

        css.push_str(&component_gtk4_css("accent", accent));
        css.push_str(&component_gtk4_css("destructive", destructive));
        css.push_str(&component_gtk4_css("warning", warning));
        css.push_str(&component_gtk4_css("success", success));
        css.push_str(&component_gtk4_css("accent", accent));
        css.push_str(&component_gtk4_css("error", destructive));

        css.push_str(&color_css("blue", palette.blue));
        css.push_str(&color_css("green", palette.green));
        css.push_str(&color_css("yellow", palette.yellow));
        css.push_str(&color_css("red", palette.red));
        css.push_str(&color_css("orange", palette.ext_orange));
        css.push_str(&color_css("purple", palette.ext_purple));
        let neutral_steps = steps(palette.neutral_5, NonZeroUsize::new(10).unwrap());
        for (i, c) in neutral_steps[..5].iter().enumerate() {
            css.push_str(&format!("@define-color light_{i} {};\n", to_hex(*c)));
        }
        for (i, c) in neutral_steps[5..].iter().enumerate() {
            css.push_str(&format!("@define-color dark_{i} {};\n", to_hex(*c)));
        }
        css
    }

    /// write the CSS to the appropriate directory
    /// Should be written in the XDG config directory for gtk-4.0
    ///
    /// # Errors
    ///
    /// Returns an `OutputError` if there is an error writing the CSS file.
    pub fn write_gtk4(&self) -> Result<(), OutputError> {
        let css_str = self.as_gtk4();
        let Some(config_dir) = dirs::config_dir() else {
            return Err(OutputError::MissingConfigDir);
        };

        let name = if self.is_dark {
            "dark.css"
        } else {
            "light.css"
        };

        let config_dir = config_dir.join("gtk-4.0").join("cosmic");
        if !config_dir.exists() {
            std::fs::create_dir_all(&config_dir).map_err(OutputError::Io)?;
        }

        let mut file = File::create(config_dir.join(name)).map_err(OutputError::Io)?;
        file.write_all(css_str.as_bytes())
            .map_err(OutputError::Io)?;

        Ok(())
    }
}

/// Trait for converting theme data into gtk4 CSS
pub trait AsGtk4Css {
    /// function for converting theme data into gtk4 CSS
    fn as_css(&self) -> String;
}

fn component_gtk4_css(prefix: &str, c: &Component) -> String {
    format!(
        r#"
@define-color {prefix}_color #{};
@define-color {prefix}_bg_color #{};
@define-color {prefix}_fg_color #{};
"#,
        to_hex(c.base),
        to_hex(c.base),
        to_hex(c.on),
    )
}

fn to_hex(c: Srgba) -> String {
    let c_u8: Rgba<palette::encoding::Srgb, u8> = c.into_format();
    format!("{:02x}{:02x}{:02x}", c_u8.red, c_u8.green, c_u8.blue)
}

fn color_css(prefix: &str, c_3: Srgba) -> String {
    let oklch: palette::Oklch = c_3.into_color();
    let c_2: Srgba = oklch.lighten(0.1).into_color();
    let c_1: Srgba = oklch.lighten(0.2).into_color();
    let c_4: Srgba = oklch.darken(0.1).into_color();
    let c_5: Srgba = oklch.darken(0.2).into_color();
    let c_1 = to_hex(c_1);
    let c_2 = to_hex(c_2);
    let c_3 = to_hex(c_3);
    let c_4 = to_hex(c_4);
    let c_5 = to_hex(c_5);

    format! {r#"
@define-color {prefix}_1 #{c_1};
@define-color {prefix}_2 #{c_2};
@define-color {prefix}_3 #{c_3};
@define-color {prefix}_4 #{c_4};
@define-color {prefix}_5 #{c_5};
"#}
}