// Copyright (c) Meta Platforms, Inc. and affiliates.

import {describe, it, expect} from 'vitest';
import {relativeLuminance, compositeOver, contrastRatio} from './contrast';
import {parseColor} from '../utils/color';

describe('relativeLuminance', () => {
  it('is 0 for black and 1 for white', () => {
    expect(relativeLuminance({r: 0, g: 0, b: 0, a: 1})).toBe(0);
    expect(relativeLuminance({r: 255, g: 255, b: 255, a: 1})).toBeCloseTo(
      1,
      10,
    );
  });

  it('weights channels per WCAG (green brightest, blue darkest)', () => {
    const red = relativeLuminance({r: 255, g: 0, b: 0, a: 1});
    const green = relativeLuminance({r: 0, g: 255, b: 0, a: 1});
    const blue = relativeLuminance({r: 0, g: 0, b: 255, a: 1});
    expect(red).toBeCloseTo(0.2126, 4);
    expect(green).toBeCloseTo(0.7152, 4);
    expect(blue).toBeCloseTo(0.0722, 4);
  });
});

describe('contrastRatio', () => {
  it('is 21 for black on white and 1 for identical colors', () => {
    expect(contrastRatio('#000000', '#FFFFFF')).toBeCloseTo(21, 5);
    expect(contrastRatio('#3B82F6', '#3B82F6')).toBe(1);
  });

  it('is symmetric in fg/bg for opaque colors', () => {
    expect(contrastRatio('#0064E0', '#FCFDFE')).toBeCloseTo(
      contrastRatio('#FCFDFE', '#0064E0'),
      10,
    );
  });

  it('matches the canonical 4.5:1 boundary gray (#767676 on white)', () => {
    const ratio = contrastRatio('#767676', '#FFFFFF');
    expect(ratio).toBeGreaterThanOrEqual(4.5);
    expect(ratio).toBeLessThan(4.6);
  });

  it('composites a translucent foreground over the background', () => {
    // 50% black over white paints as mid-gray, not black.
    const composited = contrastRatio('rgba(0, 0, 0, 0.5)', '#FFFFFF');
    expect(composited).toBeLessThan(contrastRatio('#000000', '#FFFFFF'));
    expect(composited).toBeCloseTo(
      contrastRatio('rgb(127.5, 127.5, 127.5)', '#FFFFFF'),
      10,
    );
  });

  it('rejects a translucent background', () => {
    expect(() => contrastRatio('#000000', '#FFFFFF80')).toThrow(
      /background must be opaque/,
    );
  });

  it('rejects unparseable colors', () => {
    expect(() => contrastRatio('var(--color-accent)', '#FFFFFF')).toThrow(
      /could not parse foreground/,
    );
    expect(() => contrastRatio('#000000', 'oklch(0.5 0.1 200)')).toThrow(
      /could not parse background/,
    );
  });
});

describe('compositeOver', () => {
  it('returns the foreground when opaque and the backdrop at alpha 0', () => {
    const fg = parseColor('#123456');
    const bg = parseColor('#FFFFFF');
    if (fg === null || bg === null) {
      throw new Error('fixture colors must parse');
    }
    expect(compositeOver(fg, bg)).toEqual({...fg, a: 1});
    expect(compositeOver({...fg, a: 0}, bg)).toEqual({...bg, a: 1});
  });

  it('blends in gamma-encoded sRGB space like CSS', () => {
    const fg = parseColor('rgba(0, 0, 0, 0.5)');
    const bg = parseColor('#FFFFFF');
    if (fg === null || bg === null) {
      throw new Error('fixture colors must parse');
    }
    const out = compositeOver(fg, bg);
    expect(out.r).toBeCloseTo(127.5, 5);
    expect(out.g).toBeCloseTo(127.5, 5);
    expect(out.b).toBeCloseTo(127.5, 5);
    expect(out.a).toBe(1);
  });
});