import fc from "fast-check";
import { describe, expect, it } from "vitest";

import { compositeLayers, compositeSourceOver } from "../../src/colour";
import type { BlendMode } from "../../src/colour";

describe("source-over compositing", () => {
  it("matches the canonical translucent-red-over-white result", () => {
    const result = compositeSourceOver("rgba(255, 0, 0, .5)", "white");
    expect(result.colour.coords).toEqual([1, 0.5, 0.5]);
    expect(result.colour.alpha).toBe(1);
    expect(result.hex).toBe("#ff8080");
  });

  it("composites an arbitrary RGBA reference with the source-over equation", () => {
    const result = compositeSourceOver(
      "rgba(0, 129, 255, .42)",
      "rgb(255, 255, 255)",
    );
    expect(result.colour.coords[0]).toBeCloseTo(0.58, 12);
    expect(result.colour.coords[1]).toBeCloseTo(0.7924705882352941, 12);
    expect(result.colour.coords[2]).toBe(1);
  });

  it("supports N layers and an explicit stack order", () => {
    const layers = [
      { colour: "white" },
      { colour: "rgba(255,0,0,.5)" },
      { colour: "rgba(0,0,255,.5)" },
    ];
    expect(compositeLayers(layers).hex).toBe("#8040bf");
    expect(
      compositeLayers([...layers].reverse(), { order: "top-to-bottom" }).hex,
    ).toBe("#8040bf");
  });

  it("offers visibly different sRGB and linear-light workflows", () => {
    const srgb = compositeSourceOver("rgba(255,0,0,.5)", "#00ff00", {
      space: "srgb",
    });
    const linear = compositeSourceOver("rgba(255,0,0,.5)", "#00ff00", {
      space: "linear-srgb",
    });
    expect(srgb.hex).toBe("#808000");
    expect(linear.hex).toBe("#bcbc00");
  });

  it("implements opacity and common blend modes", () => {
    expect(
      compositeSourceOver("#ff0000", "#808080", { blendMode: "multiply" }).hex,
    ).toBe("#800000");
    expect(
      compositeSourceOver("#ff0000", "#808080", { blendMode: "screen" }).hex,
    ).toBe("#ff8080");
    expect(compositeSourceOver("#ff0000", "#ffffff", { opacity: 0 }).hex).toBe(
      "#ffffff",
    );
  });

  it("keeps every exposed blend mode renderable", () => {
    const modes: BlendMode[] = [
      "normal",
      "multiply",
      "screen",
      "overlay",
      "darken",
      "lighten",
      "color-dodge",
      "color-burn",
      "hard-light",
      "soft-light",
      "difference",
      "exclusion",
      "hue",
      "saturation",
      "color",
      "luminosity",
    ];
    for (const blendMode of modes) {
      const result = compositeSourceOver("rgba(230,30,80,.7)", "#2878c8", {
        blendMode,
      });
      expect(result.colour.coords.every(Number.isFinite), blendMode).toBe(true);
      expect(result.hex, blendMode).toMatch(/^#[0-9a-f]{6}$/);
    }
  });

  it("keeps arbitrary composites bounded and alpha-correct", () => {
    fc.assert(
      fc.property(
        fc.tuple(
          fc.double({ min: 0, max: 1, noNaN: true }),
          fc.double({ min: 0, max: 1, noNaN: true }),
          fc.double({ min: 0, max: 1, noNaN: true }),
          fc.double({ min: 0, max: 1, noNaN: true }),
        ),
        fc.tuple(
          fc.double({ min: 0, max: 1, noNaN: true }),
          fc.double({ min: 0, max: 1, noNaN: true }),
          fc.double({ min: 0, max: 1, noNaN: true }),
          fc.double({ min: 0, max: 1, noNaN: true }),
        ),
        (foreground, background) => {
          const result = compositeSourceOver(
            {
              space: "srgb",
              coords: foreground.slice(0, 3) as [number, number, number],
              alpha: foreground[3],
            },
            {
              space: "srgb",
              coords: background.slice(0, 3) as [number, number, number],
              alpha: background[3],
            },
          ).colour;
          expect(
            result.coords.every((channel) => channel >= 0 && channel <= 1),
          ).toBe(true);
          expect(result.alpha).toBeGreaterThanOrEqual(0);
          expect(result.alpha).toBeLessThanOrEqual(1);
          expect(result.alpha).toBeCloseTo(
            foreground[3] + background[3] * (1 - foreground[3]),
            12,
          );
        },
      ),
      { numRuns: 100 },
    );
  });
});