bchen-ui/tests/tokens.test.ts

import { describe, it, expect } from 'vitest';
import { readFileSync } from 'fs';

const css = readFileSync(new URL('../dist/tokens.css', import.meta.url), 'utf-8');

// ---- CSS parser helpers ----

function extractRootBlock(src: string): string {
  const m = src.match(/:root\s*\{([^}]+)\}/);
  return m?.[1] ?? '';
}

function extractDarkBlock(src: string): string {
  const afterMedia = src.split('@media (prefers-color-scheme: dark)')[1] ?? '';
  const m = afterMedia.match(/:root\s*\{([^}]+)\}/);
  return m?.[1] ?? '';
}

function parseProps(block: string): Map<string, string> {
  const map = new Map<string, string>();
  const re = /--([\w-]+)\s*:\s*([^;]+);/g;
  let m: RegExpExecArray | null;
  while ((m = re.exec(block)) !== null) {
    map.set(`--${m[1]}`, m[2].trim());
  }
  return map;
}

function resolveToken(value: string, props: Map<string, string>): string {
  const varRe = /var\(--([\w-]+)\)/;
  let v = value;
  for (let i = 0; i < 10 && varRe.test(v); i++) {
    v = v.replace(varRe, (_, name) => props.get(`--${name}`) ?? 'unresolved');
  }
  return v.trim();
}

// ---- WCAG contrast helpers ----

function expandHex(hex: string): string {
  const h = hex.replace('#', '');
  return h.length === 3
    ? `#${h[0]}${h[0]}${h[1]}${h[1]}${h[2]}${h[2]}`
    : `#${h}`;
}

function luminance(hex: string): number {
  const h = expandHex(hex).replace('#', '');
  const r = parseInt(h.slice(0, 2), 16) / 255;
  const g = parseInt(h.slice(2, 4), 16) / 255;
  const b = parseInt(h.slice(4, 6), 16) / 255;
  const lin = (c: number) =>
    c <= 0.04045 ? c / 12.92 : ((c + 0.055) / 1.055) ** 2.4;
  return 0.2126 * lin(r) + 0.7152 * lin(g) + 0.0722 * lin(b);
}

function contrast(hex1: string, hex2: string): number {
  const l1 = luminance(hex1);
  const l2 = luminance(hex2);
  const [lighter, darker] = l1 > l2 ? [l1, l2] : [l2, l1];
  return (lighter + 0.05) / (darker + 0.05);
}

// ---- Fixtures ----

const rootProps = parseProps(extractRootBlock(css));
const darkProps = parseProps(extractDarkBlock(css));
// Merged: dark overrides on top of light primitives so var() refs resolve correctly.
const mergedDark = new Map([...rootProps, ...darkProps]);

// Tokens that must be explicitly defined in both light and dark blocks.
const DARK_MODE_TOKENS = [
  '--bg', '--bg-elevated', '--surface',
  '--fg', '--fg-muted',
  '--border-color', '--border-strong',
  '--accent', '--accent-fg', '--accent-hover',
  '--danger', '--danger-fg', '--danger-bg',
  '--input-bg', '--input-fg', '--input-border', '--input-bg-focus',
];

// ---- Tests ----

describe('tokens.css — token presence', () => {
  it('defines all dark-mode tokens in :root (light)', () => {
    for (const token of DARK_MODE_TOKENS) {
      expect(rootProps.has(token), `${token} missing from :root`).toBe(true);
    }
  });

  it('defines all dark-mode tokens in @media (prefers-color-scheme: dark)', () => {
    for (const token of DARK_MODE_TOKENS) {
      expect(darkProps.has(token), `${token} missing from @media dark`).toBe(true);
    }
  });
});

describe('tokens.css — WCAG AA contrast (light)', () => {
  const fg = resolveToken(rootProps.get('--fg')!, rootProps);
  const fgMuted = resolveToken(rootProps.get('--fg-muted')!, rootProps);
  const bg = resolveToken(rootProps.get('--bg')!, rootProps);
  const borderStrong = resolveToken(rootProps.get('--border-strong')!, rootProps);

  it('--fg on --bg >= 4.5:1', () => {
    expect(contrast(fg, bg)).toBeGreaterThanOrEqual(4.5);
  });

  it('--fg-muted on --bg >= 4.5:1', () => {
    expect(contrast(fgMuted, bg)).toBeGreaterThanOrEqual(4.5);
  });

  it('--border-strong on --bg >= 3.0:1 (UI contrast)', () => {
    expect(contrast(borderStrong, bg)).toBeGreaterThanOrEqual(3.0);
  });
});

describe('tokens.css — WCAG AA contrast (dark)', () => {
  const fg = resolveToken(mergedDark.get('--fg')!, mergedDark);
  const fgMuted = resolveToken(mergedDark.get('--fg-muted')!, mergedDark);
  const bg = resolveToken(mergedDark.get('--bg')!, mergedDark);
  const borderStrong = resolveToken(mergedDark.get('--border-strong')!, mergedDark);

  it('--fg on --bg >= 4.5:1', () => {
    expect(contrast(fg, bg)).toBeGreaterThanOrEqual(4.5);
  });

  it('--fg-muted on --bg >= 4.5:1', () => {
    expect(contrast(fgMuted, bg)).toBeGreaterThanOrEqual(4.5);
  });

  it('--border-strong on --bg >= 3.0:1 (UI contrast)', () => {
    expect(contrast(borderStrong, bg)).toBeGreaterThanOrEqual(3.0);
  });
});