use egui::{Color32, Image, ImageSource, Response, Sense, TextureOptions, Ui, Widget};

pub const GENERIC_PALETTE: [u8; 4] = [0, 64, 128, 255];

pub fn shade(brt: u8, color: Color32) -> Color32 {
    color.gamma_multiply(brt as f32 / 255.0)
}

pub fn generic_palette(color: Color32) -> [Color32; 4] {
    GENERIC_PALETTE.map(|brt| shade(brt, color))
}

pub const fn parse_palette(palette: u8) -> [u8; 4] {
    [
        0,
        (palette >> 2) & 0x03,
        (palette >> 4) & 0x03,
        (palette >> 6) & 0x03,
    ]
}

pub const fn parse_shades(brts: &[u8; 8]) -> [u8; 4] {
    [
        0,
        brts[0],
        brts[2],
        brts[0].saturating_add(brts[2]).saturating_add(brts[4]),
    ]
}

pub fn parse_brts(brts: &[u16; 3], color: Color32) -> [Color32; 4] {
    [
        Color32::BLACK,
        shade(brts[0] as u8, color),
        shade(brts[1] as u8, color),
        shade((brts[0] + brts[1] + brts[2]) as u8, color),
    ]
}

pub fn palette_colors(palette: u8, brts: &[u8; 8], color: Color32) -> [Color32; 4] {
    let colors = parse_shades(brts).map(|s| shade(s, color));
    parse_palette(palette).map(|p| colors[p as usize])
}

pub struct Object {
    pub x: i16,
    pub lon: bool,
    pub ron: bool,
    pub parallax: i16,
    pub y: i16,
    pub data: CellData,
}

impl Object {
    pub fn parse(object: [u16; 4]) -> Self {
        let x = ((object[0] & 0x03ff) << 6 >> 6) as i16;
        let parallax = ((object[1] & 0x03ff) << 6 >> 6) as i16;
        let lon = object[1] & 0x8000 != 0;
        let ron = object[1] & 0x4000 != 0;
        let y = (object[2] & 0x00ff) as i16;
        // Y is stored as the bottom 8 bits of an i16,
        // so only sign extend if it's out of range.
        let y = if y > 224 { y << 8 >> 8 } else { y };
        let data = CellData::parse(object[3]);
        Self {
            x,
            lon,
            ron,
            parallax,
            y,
            data,
        }
    }

    pub fn update(&self, source: &mut [u16; 4]) -> bool {
        let mut changed = false;

        let new_x = (self.x as u16 & 0x03ff) | (source[0] & 0xfc00);
        changed |= source[0] != new_x;
        source[0] = new_x;

        let new_p = if self.lon { 0x8000 } else { 0x0000 }
            | if self.ron { 0x4000 } else { 0x0000 }
            | (self.parallax as u16 & 0x3ff)
            | (source[1] & 0x3c00);
        changed |= source[1] != new_p;
        source[1] = new_p;

        let new_y = (self.y as u16 & 0x00ff) | (source[2] & 0xff00);
        changed |= source[2] != new_y;
        source[2] = new_y;

        if self.data.update(&mut source[3]) {
            changed = true;
        }
        changed
    }
}

pub struct CellData {
    pub palette_index: usize,
    pub hflip: bool,
    pub vflip: bool,
    pub char_index: usize,
}

impl CellData {
    pub fn parse(cell: u16) -> Self {
        let char_index = (cell & 0x7ff) as usize;
        let vflip = cell & 0x1000 != 0;
        let hflip = cell & 0x2000 != 0;
        let palette_index = (cell >> 14) as usize;
        Self {
            char_index,
            vflip,
            hflip,
            palette_index,
        }
    }

    pub fn update(&self, source: &mut u16) -> bool {
        let new_value = (self.palette_index as u16) << 14
            | if self.hflip { 0x2000 } else { 0x0000 }
            | if self.vflip { 0x1000 } else { 0x0000 }
            | (self.char_index as u16 & 0x07ff)
            | (*source & 0x0800);
        let changed = *source != new_value;
        *source = new_value;
        changed
    }
}

pub fn read_char_row(
    char: &[u16; 8],
    hflip: bool,
    vflip: bool,
    row: usize,
) -> impl Iterator<Item = u8> {
    let pixels = if vflip { char[7 - row] } else { char[row] };
    (0..16).step_by(2).map(move |i| {
        let pixel = if hflip { 14 - i } else { i };
        ((pixels >> pixel) & 0x3) as u8
    })
}

pub fn read_char_pixel(char: &[u16; 8], hflip: bool, vflip: bool, row: usize, col: usize) -> u8 {
    let pixels = if vflip { char[7 - row] } else { char[row] };
    let pixel = if hflip { 7 - col } else { col } << 1;
    ((pixels >> pixel) & 0x3) as u8
}

pub struct CharacterGrid<'a> {
    source: ImageSource<'a>,
    scale: f32,
    show_grid: bool,
    selected: Option<usize>,
}

impl<'a> CharacterGrid<'a> {
    pub fn new(source: impl Into<ImageSource<'a>>) -> Self {
        Self {
            source: source.into(),
            scale: 1.0,
            show_grid: false,
            selected: None,
        }
    }

    pub fn with_scale(self, scale: f32) -> Self {
        Self { scale, ..self }
    }

    pub fn with_grid(self, show_grid: bool) -> Self {
        Self { show_grid, ..self }
    }

    pub fn with_selected(self, selected: usize) -> Self {
        Self {
            selected: Some(selected),
            ..self
        }
    }

    pub fn show(self, ui: &mut Ui) -> Option<usize> {
        let start_pos = ui.cursor().min;
        let cell_size = 8.0 * self.scale;

        let res = self.ui(ui);

        let grid_width_cells = ((res.rect.max.x - res.rect.min.x) / cell_size).round() as usize;

        if res.clicked() {
            let click_pos = res.interact_pointer_pos()?;
            let grid_pos = (click_pos - start_pos) / cell_size;
            Some((grid_pos.y as usize * grid_width_cells) + grid_pos.x as usize)
        } else {
            None
        }
    }
}

impl Widget for CharacterGrid<'_> {
    fn ui(self, ui: &mut Ui) -> Response {
        let image = Image::new(self.source)
            .fit_to_original_size(self.scale)
            .texture_options(TextureOptions::NEAREST)
            .sense(Sense::click());
        let res = ui.add(image);

        let cell_size = 8.0 * self.scale;
        let grid_width_cells = ((res.rect.max.x - res.rect.min.x) / cell_size).round() as usize;
        let grid_height_cells = ((res.rect.max.y - res.rect.min.y) / cell_size).round() as usize;

        let painter = ui.painter_at(res.rect);
        if self.show_grid {
            let stroke = ui.style().visuals.widgets.noninteractive.fg_stroke;
            for x in (1..grid_width_cells).map(|i| (i as f32) * cell_size) {
                let p1 = (res.rect.min.x + x, res.rect.min.y).into();
                let p2 = (res.rect.min.x + x, res.rect.max.y).into();
                painter.line(vec![p1, p2], stroke);
            }
            for y in (1..grid_height_cells).map(|i| (i as f32) * cell_size) {
                let p1 = (res.rect.min.x, res.rect.min.y + y).into();
                let p2 = (res.rect.max.x, res.rect.min.y + y).into();
                painter.line(vec![p1, p2], stroke);
            }
        }
        if let Some(selected) = self.selected {
            let x1 = (selected % grid_width_cells) as f32 * cell_size;
            let x2 = x1 + cell_size;
            let y1 = (selected / grid_width_cells) as f32 * cell_size;
            let y2 = y1 + cell_size;
            painter.line(
                vec![
                    (res.rect.min + (x1, y1).into()),
                    (res.rect.min + (x2, y1).into()),
                    (res.rect.min + (x2, y2).into()),
                    (res.rect.min + (x1, y2).into()),
                    (res.rect.min + (x1, y1).into()),
                ],
                ui.style().visuals.widgets.active.fg_stroke,
            );
        }
        res
    }
}