/// Bitmap font atlas for ASCII 32-126.
/// 8x12 pixel glyphs arranged in 16 columns x 6 rows = 128x72 texture.
pub struct FontAtlas {
    pub width: u32,
    pub height: u32,
    pub glyph_width: u32,
    pub glyph_height: u32,
    pub pixels: Vec<u8>, // R8 grayscale
}

/// Classic 8x12 PC BIOS bitmap font data for ASCII 32-126 (95 characters).
/// Each character is 12 bytes (one byte per row, MSB = leftmost pixel).
#[rustfmt::skip]
const FONT_DATA: [u8; 95 * 12] = [
    // 32: Space
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 33: !
    0x00, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x00, 0x18, 0x00, 0x00, 0x00,
    // 34: "
    0x00, 0x6C, 0x6C, 0x24, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 35: #
    0x00, 0x6C, 0x6C, 0xFE, 0x6C, 0xFE, 0x6C, 0x6C, 0x00, 0x00, 0x00, 0x00,
    // 36: $
    0x00, 0x18, 0x3E, 0x60, 0x3C, 0x06, 0x7C, 0x18, 0x00, 0x00, 0x00, 0x00,
    // 37: %
    0x00, 0x00, 0x62, 0x64, 0x08, 0x10, 0x26, 0x46, 0x00, 0x00, 0x00, 0x00,
    // 38: &
    0x00, 0x30, 0x48, 0x48, 0x30, 0x4A, 0x44, 0x3A, 0x00, 0x00, 0x00, 0x00,
    // 39: '
    0x00, 0x18, 0x18, 0x30, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 40: (
    0x00, 0x0C, 0x18, 0x30, 0x30, 0x30, 0x18, 0x0C, 0x00, 0x00, 0x00, 0x00,
    // 41: )
    0x00, 0x30, 0x18, 0x0C, 0x0C, 0x0C, 0x18, 0x30, 0x00, 0x00, 0x00, 0x00,
    // 42: *
    0x00, 0x00, 0x66, 0x3C, 0xFF, 0x3C, 0x66, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 43: +
    0x00, 0x00, 0x18, 0x18, 0x7E, 0x18, 0x18, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 44: ,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x18, 0x18, 0x30, 0x00, 0x00, 0x00,
    // 45: -
    0x00, 0x00, 0x00, 0x00, 0x7E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 46: .
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x18, 0x18, 0x00, 0x00, 0x00, 0x00,
    // 47: /
    0x00, 0x02, 0x06, 0x0C, 0x18, 0x30, 0x60, 0x40, 0x00, 0x00, 0x00, 0x00,
    // 48: 0
    0x00, 0x3C, 0x66, 0x6E, 0x7E, 0x76, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 49: 1
    0x00, 0x18, 0x38, 0x18, 0x18, 0x18, 0x18, 0x7E, 0x00, 0x00, 0x00, 0x00,
    // 50: 2
    0x00, 0x3C, 0x66, 0x06, 0x0C, 0x18, 0x30, 0x7E, 0x00, 0x00, 0x00, 0x00,
    // 51: 3
    0x00, 0x3C, 0x66, 0x06, 0x1C, 0x06, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 52: 4
    0x00, 0x0C, 0x1C, 0x2C, 0x4C, 0x7E, 0x0C, 0x0C, 0x00, 0x00, 0x00, 0x00,
    // 53: 5
    0x00, 0x7E, 0x60, 0x7C, 0x06, 0x06, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 54: 6
    0x00, 0x1C, 0x30, 0x60, 0x7C, 0x66, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 55: 7
    0x00, 0x7E, 0x06, 0x0C, 0x18, 0x30, 0x30, 0x30, 0x00, 0x00, 0x00, 0x00,
    // 56: 8
    0x00, 0x3C, 0x66, 0x66, 0x3C, 0x66, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 57: 9
    0x00, 0x3C, 0x66, 0x66, 0x3E, 0x06, 0x0C, 0x38, 0x00, 0x00, 0x00, 0x00,
    // 58: :
    0x00, 0x00, 0x18, 0x18, 0x00, 0x18, 0x18, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 59: ;
    0x00, 0x00, 0x18, 0x18, 0x00, 0x18, 0x18, 0x30, 0x00, 0x00, 0x00, 0x00,
    // 60: <
    0x00, 0x06, 0x0C, 0x18, 0x30, 0x18, 0x0C, 0x06, 0x00, 0x00, 0x00, 0x00,
    // 61: =
    0x00, 0x00, 0x00, 0x7E, 0x00, 0x7E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 62: >
    0x00, 0x60, 0x30, 0x18, 0x0C, 0x18, 0x30, 0x60, 0x00, 0x00, 0x00, 0x00,
    // 63: ?
    0x00, 0x3C, 0x66, 0x06, 0x0C, 0x18, 0x00, 0x18, 0x00, 0x00, 0x00, 0x00,
    // 64: @
    0x00, 0x3C, 0x66, 0x6E, 0x6A, 0x6E, 0x60, 0x3E, 0x00, 0x00, 0x00, 0x00,
    // 65: A
    0x00, 0x18, 0x3C, 0x66, 0x66, 0x7E, 0x66, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 66: B
    0x00, 0x7C, 0x66, 0x66, 0x7C, 0x66, 0x66, 0x7C, 0x00, 0x00, 0x00, 0x00,
    // 67: C
    0x00, 0x3C, 0x66, 0x60, 0x60, 0x60, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 68: D
    0x00, 0x78, 0x6C, 0x66, 0x66, 0x66, 0x6C, 0x78, 0x00, 0x00, 0x00, 0x00,
    // 69: E
    0x00, 0x7E, 0x60, 0x60, 0x7C, 0x60, 0x60, 0x7E, 0x00, 0x00, 0x00, 0x00,
    // 70: F
    0x00, 0x7E, 0x60, 0x60, 0x7C, 0x60, 0x60, 0x60, 0x00, 0x00, 0x00, 0x00,
    // 71: G
    0x00, 0x3C, 0x66, 0x60, 0x6E, 0x66, 0x66, 0x3E, 0x00, 0x00, 0x00, 0x00,
    // 72: H
    0x00, 0x66, 0x66, 0x66, 0x7E, 0x66, 0x66, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 73: I
    0x00, 0x7E, 0x18, 0x18, 0x18, 0x18, 0x18, 0x7E, 0x00, 0x00, 0x00, 0x00,
    // 74: J
    0x00, 0x06, 0x06, 0x06, 0x06, 0x06, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 75: K
    0x00, 0x66, 0x6C, 0x78, 0x70, 0x78, 0x6C, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 76: L
    0x00, 0x60, 0x60, 0x60, 0x60, 0x60, 0x60, 0x7E, 0x00, 0x00, 0x00, 0x00,
    // 77: M
    0x00, 0xC6, 0xEE, 0xFE, 0xD6, 0xC6, 0xC6, 0xC6, 0x00, 0x00, 0x00, 0x00,
    // 78: N
    0x00, 0x66, 0x76, 0x7E, 0x7E, 0x6E, 0x66, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 79: O
    0x00, 0x3C, 0x66, 0x66, 0x66, 0x66, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 80: P
    0x00, 0x7C, 0x66, 0x66, 0x7C, 0x60, 0x60, 0x60, 0x00, 0x00, 0x00, 0x00,
    // 81: Q
    0x00, 0x3C, 0x66, 0x66, 0x66, 0x6A, 0x6C, 0x36, 0x00, 0x00, 0x00, 0x00,
    // 82: R
    0x00, 0x7C, 0x66, 0x66, 0x7C, 0x6C, 0x66, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 83: S
    0x00, 0x3C, 0x66, 0x60, 0x3C, 0x06, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 84: T
    0x00, 0x7E, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x00, 0x00, 0x00, 0x00,
    // 85: U
    0x00, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 86: V
    0x00, 0x66, 0x66, 0x66, 0x66, 0x66, 0x3C, 0x18, 0x00, 0x00, 0x00, 0x00,
    // 87: W
    0x00, 0xC6, 0xC6, 0xC6, 0xD6, 0xFE, 0xEE, 0xC6, 0x00, 0x00, 0x00, 0x00,
    // 88: X
    0x00, 0x66, 0x66, 0x3C, 0x18, 0x3C, 0x66, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 89: Y
    0x00, 0x66, 0x66, 0x66, 0x3C, 0x18, 0x18, 0x18, 0x00, 0x00, 0x00, 0x00,
    // 90: Z
    0x00, 0x7E, 0x06, 0x0C, 0x18, 0x30, 0x60, 0x7E, 0x00, 0x00, 0x00, 0x00,
    // 91: [
    0x00, 0x3C, 0x30, 0x30, 0x30, 0x30, 0x30, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 92: backslash
    0x00, 0x40, 0x60, 0x30, 0x18, 0x0C, 0x06, 0x02, 0x00, 0x00, 0x00, 0x00,
    // 93: ]
    0x00, 0x3C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 94: ^
    0x00, 0x18, 0x3C, 0x66, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 95: _
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00, 0x00, 0x00,
    // 96: `
    0x00, 0x30, 0x18, 0x0C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    // 97: a
    0x00, 0x00, 0x00, 0x3C, 0x06, 0x3E, 0x66, 0x3E, 0x00, 0x00, 0x00, 0x00,
    // 98: b
    0x00, 0x60, 0x60, 0x7C, 0x66, 0x66, 0x66, 0x7C, 0x00, 0x00, 0x00, 0x00,
    // 99: c
    0x00, 0x00, 0x00, 0x3C, 0x66, 0x60, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 100: d
    0x00, 0x06, 0x06, 0x3E, 0x66, 0x66, 0x66, 0x3E, 0x00, 0x00, 0x00, 0x00,
    // 101: e
    0x00, 0x00, 0x00, 0x3C, 0x66, 0x7E, 0x60, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 102: f
    0x00, 0x1C, 0x30, 0x30, 0x7C, 0x30, 0x30, 0x30, 0x00, 0x00, 0x00, 0x00,
    // 103: g
    0x00, 0x00, 0x00, 0x3E, 0x66, 0x66, 0x3E, 0x06, 0x3C, 0x00, 0x00, 0x00,
    // 104: h
    0x00, 0x60, 0x60, 0x7C, 0x66, 0x66, 0x66, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 105: i
    0x00, 0x18, 0x00, 0x38, 0x18, 0x18, 0x18, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 106: j
    0x00, 0x0C, 0x00, 0x1C, 0x0C, 0x0C, 0x0C, 0x0C, 0x78, 0x00, 0x00, 0x00,
    // 107: k
    0x00, 0x60, 0x60, 0x66, 0x6C, 0x78, 0x6C, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 108: l
    0x00, 0x38, 0x18, 0x18, 0x18, 0x18, 0x18, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 109: m
    0x00, 0x00, 0x00, 0xEC, 0xFE, 0xD6, 0xC6, 0xC6, 0x00, 0x00, 0x00, 0x00,
    // 110: n
    0x00, 0x00, 0x00, 0x7C, 0x66, 0x66, 0x66, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 111: o
    0x00, 0x00, 0x00, 0x3C, 0x66, 0x66, 0x66, 0x3C, 0x00, 0x00, 0x00, 0x00,
    // 112: p
    0x00, 0x00, 0x00, 0x7C, 0x66, 0x66, 0x7C, 0x60, 0x60, 0x00, 0x00, 0x00,
    // 113: q
    0x00, 0x00, 0x00, 0x3E, 0x66, 0x66, 0x3E, 0x06, 0x06, 0x00, 0x00, 0x00,
    // 114: r
    0x00, 0x00, 0x00, 0x7C, 0x66, 0x60, 0x60, 0x60, 0x00, 0x00, 0x00, 0x00,
    // 115: s
    0x00, 0x00, 0x00, 0x3E, 0x60, 0x3C, 0x06, 0x7C, 0x00, 0x00, 0x00, 0x00,
    // 116: t
    0x00, 0x30, 0x30, 0x7C, 0x30, 0x30, 0x30, 0x1C, 0x00, 0x00, 0x00, 0x00,
    // 117: u
    0x00, 0x00, 0x00, 0x66, 0x66, 0x66, 0x66, 0x3E, 0x00, 0x00, 0x00, 0x00,
    // 118: v
    0x00, 0x00, 0x00, 0x66, 0x66, 0x66, 0x3C, 0x18, 0x00, 0x00, 0x00, 0x00,
    // 119: w
    0x00, 0x00, 0x00, 0xC6, 0xC6, 0xD6, 0xFE, 0x6C, 0x00, 0x00, 0x00, 0x00,
    // 120: x
    0x00, 0x00, 0x00, 0x66, 0x3C, 0x18, 0x3C, 0x66, 0x00, 0x00, 0x00, 0x00,
    // 121: y
    0x00, 0x00, 0x00, 0x66, 0x66, 0x66, 0x3E, 0x06, 0x3C, 0x00, 0x00, 0x00,
    // 122: z
    0x00, 0x00, 0x00, 0x7E, 0x0C, 0x18, 0x30, 0x7E, 0x00, 0x00, 0x00, 0x00,
    // 123: {
    0x00, 0x0E, 0x18, 0x18, 0x70, 0x18, 0x18, 0x0E, 0x00, 0x00, 0x00, 0x00,
    // 124: |
    0x00, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x00, 0x00, 0x00, 0x00,
    // 125: }
    0x00, 0x70, 0x18, 0x18, 0x0E, 0x18, 0x18, 0x70, 0x00, 0x00, 0x00, 0x00,
    // 126: ~
    0x00, 0x32, 0x4C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
];

impl FontAtlas {
    /// Generate a bitmap font atlas with real 8x12 PC BIOS-style glyphs.
    /// Each glyph is 8x12 pixels. Atlas is 16 cols x 6 rows = 128x72.
    pub fn generate() -> Self {
        let glyph_width: u32 = 8;
        let glyph_height: u32 = 12;
        let cols: u32 = 16;
        let rows: u32 = 6;
        let width = cols * glyph_width;   // 128
        let height = rows * glyph_height; // 72

        let mut pixels = vec![0u8; (width * height) as usize];

        // Unpack 1-bit-per-pixel FONT_DATA into R8 pixel atlas
        for code in 32u8..=126u8 {
            let index = (code - 32) as u32;
            let col = index % cols;
            let row = index / cols;
            let base_x = col * glyph_width;
            let base_y = row * glyph_height;
            let data_offset = (index as usize) * 12;

            for py in 0..12u32 {
                let row_byte = FONT_DATA[data_offset + py as usize];
                for px in 0..8u32 {
                    if (row_byte >> (7 - px)) & 1 != 0 {
                        let pixel_idx = ((base_y + py) * width + (base_x + px)) as usize;
                        pixels[pixel_idx] = 255;
                    }
                }
            }
        }

        // Ensure pixel (0,0) is white (255) so solid-color rects can sample
        // UV (0,0) and get full brightness for tinting.
        pixels[0] = 255;

        FontAtlas {
            width,
            height,
            glyph_width,
            glyph_height,
            pixels,
        }
    }

    /// Returns (u0, v0, u1, v1) UV coordinates for a given character.
    /// Returns coordinates for space if character is out of ASCII range.
    pub fn glyph_uv(&self, ch: char) -> (f32, f32, f32, f32) {
        let code = ch as u32;
        let index = if code >= 32 && code <= 126 {
            code - 32
        } else {
            0 // space
        };

        let cols = self.width / self.glyph_width;
        let col = index % cols;
        let row = index / cols;

        let u0 = (col * self.glyph_width) as f32 / self.width as f32;
        let v0 = (row * self.glyph_height) as f32 / self.height as f32;
        let u1 = u0 + self.glyph_width as f32 / self.width as f32;
        let v1 = v0 + self.glyph_height as f32 / self.height as f32;

        (u0, v0, u1, v1)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_generate_size() {
        let atlas = FontAtlas::generate();
        assert_eq!(atlas.width, 128);
        assert_eq!(atlas.height, 72);
        assert_eq!(atlas.pixels.len(), (128 * 72) as usize);
    }

    #[test]
    fn test_glyph_uv_space() {
        let atlas = FontAtlas::generate();
        let (u0, v0, u1, v1) = atlas.glyph_uv(' ');
        assert!((u0 - 0.0).abs() < 1e-6);
        assert!((v0 - 0.0).abs() < 1e-6);
        assert!((u1 - 8.0 / 128.0).abs() < 1e-6);
        assert!((v1 - 12.0 / 72.0).abs() < 1e-6);
    }

    #[test]
    fn test_glyph_uv_a() {
        let atlas = FontAtlas::generate();
        // 'A' = ASCII 65, index = 65 - 32 = 33
        // col = 33 % 16 = 1, row = 33 / 16 = 2
        let (u0, v0, u1, v1) = atlas.glyph_uv('A');
        let expected_u0 = 1.0 * 8.0 / 128.0;
        let expected_v0 = 2.0 * 12.0 / 72.0;
        let expected_u1 = expected_u0 + 8.0 / 128.0;
        let expected_v1 = expected_v0 + 12.0 / 72.0;
        assert!((u0 - expected_u0).abs() < 1e-6, "u0 mismatch: {} vs {}", u0, expected_u0);
        assert!((v0 - expected_v0).abs() < 1e-6, "v0 mismatch: {} vs {}", v0, expected_v0);
        assert!((u1 - expected_u1).abs() < 1e-6);
        assert!((v1 - expected_v1).abs() < 1e-6);
    }
}