export interface Rgba {
  r: number;
  g: number;
  b: number;
  a: number;
}

const NAMED: Record<string, string> = {
  black: "#000000",
  white: "#ffffff",
  red: "#ff0000",
  green: "#008000",
  blue: "#0000ff",
  yellow: "#ffff00",
  orange: "#ffa500",
  purple: "#800080",
  gray: "#808080",
  grey: "#808080",
  silver: "#c0c0c0",
  maroon: "#800000",
  olive: "#808000",
  lime: "#00ff00",
  aqua: "#00ffff",
  teal: "#008080",
  navy: "#000080",
  fuchsia: "#ff00ff",
  cyan: "#00ffff",
  gold: "#ffd700",
};

export function parseColor(value: string): Rgba | null {
  const v = value.trim().toLowerCase();
  if (v === "transparent") {
    return { r: 0, g: 0, b: 0, a: 0 };
  }
  const named = NAMED[v];
  if (named) {
    return parseColor(named);
  }
  const hexMatch = v.match(/^#([0-9a-f]{3,8})$/);
  if (hexMatch) {
    const hex = hexMatch[1] ?? "";
    if (hex.length === 3 || hex.length === 4) {
      return {
        r: Number.parseInt(`${hex[0]}${hex[0]}`, 16),
        g: Number.parseInt(`${hex[1]}${hex[1]}`, 16),
        b: Number.parseInt(`${hex[2]}${hex[2]}`, 16),
        a: hex.length === 4 ? Number.parseInt(`${hex[3]}${hex[3]}`, 16) / 255 : 1,
      };
    }
    if (hex.length === 6 || hex.length === 8) {
      return {
        r: Number.parseInt(hex.slice(0, 2), 16),
        g: Number.parseInt(hex.slice(2, 4), 16),
        b: Number.parseInt(hex.slice(4, 6), 16),
        a: hex.length === 8 ? Number.parseInt(hex.slice(6, 8), 16) / 255 : 1,
      };
    }
    return null;
  }
  const fnMatch = v.match(/^rgba?\(([^)]*)\)$/);
  if (fnMatch) {
    const parts = (fnMatch[1] ?? "").split(/[\s,/]+/).filter(Boolean);
    if (parts.length < 3) {
      return null;
    }
    const channel = (raw: string): number =>
      raw.endsWith("%")
        ? Math.round((Number.parseFloat(raw) / 100) * 255)
        : Math.round(Number.parseFloat(raw));
    const r = channel(parts[0] ?? "");
    const g = channel(parts[1] ?? "");
    const b = channel(parts[2] ?? "");
    const alphaRaw = parts[3];
    const a =
      alphaRaw === undefined
        ? 1
        : alphaRaw.endsWith("%")
          ? Number.parseFloat(alphaRaw) / 100
          : Number.parseFloat(alphaRaw);
    if ([r, g, b].some((n) => Number.isNaN(n)) || Number.isNaN(a)) {
      return null;
    }
    return { r, g, b, a: Math.min(Math.max(a, 0), 1) };
  }
  return null;
}

export function blend(fg: Rgba, bg: Rgba): Rgba {
  const a = fg.a + bg.a * (1 - fg.a);
  if (a === 0) {
    return { r: 0, g: 0, b: 0, a: 0 };
  }
  const mix = (f: number, b: number): number => Math.round((f * fg.a + b * bg.a * (1 - fg.a)) / a);
  return { r: mix(fg.r, bg.r), g: mix(fg.g, bg.g), b: mix(fg.b, bg.b), a };
}

export function rgbDistance(a: Rgba, b: Rgba): number {
  return Math.hypot(a.r - b.r, a.g - b.g, a.b - b.b);
}

export function toHex(color: Rgba): string {
  const part = (n: number): string => n.toString(16).padStart(2, "0");
  return `#${part(color.r)}${part(color.g)}${part(color.b)}`;
}