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 fn parse_palette(palette: u8, brts: &[u8], color: Color32) -> [Color32; 4] {
    let shades = [
        Color32::BLACK,
        shade(brts[0], color),
        shade(brts[2], color),
        shade(
            brts[0].saturating_add(brts[2]).saturating_add(brts[4]),
            color,
        ),
    ];
    [
        Color32::BLACK,
        shades[(palette >> 2) as usize & 0x03],
        shades[(palette >> 4) as usize & 0x03],
        shades[(palette >> 6) as usize & 0x03],
    ]
}

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

pub fn read_char_row(
    char: &[u16],
    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 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
    }
}