freezmo/tests/contrast.mjs

/**
 * Contrast diagnostic (NOT part of `npm run test:e2e`): axe cannot judge text
 * on a blurred glass surface — it reports those nodes as "incomplete" — so
 * this samples the **rendered pixels** instead.
 *
 * For every text element it takes a screenshot of that element's box, finds
 * the dominant colour in it (the background: glyphs are the minority of the
 * pixels) and compares it with the text colour from the computed style using
 * the WCAG relative-luminance formula. Large text (>= 24px, or >= 18.66px
 * bold) is held to 3:1, everything else to 4.5:1.
 *
 *   node tests/contrast.mjs            # every screen, both themes
 *   node tests/contrast.mjs study      # filter by screen name
 *
 * It always exits 0 — the numbers are for tuning the palette.
 */
import { BASE, DECK, launchBrowser, makePage, seed } from "./lib.mjs";

const filter = process.argv[2] ?? "";
const browser = await launchBrowser();
const failures = [];

/** WCAG relative luminance of an [r, g, b] triple (0-255). */
const LUMINANCE = `
  const luminance = ([r, g, b]) => {
    const channel = (value) => {
      const v = value / 255;
      return v <= 0.03928 ? v / 12.92 : Math.pow((v + 0.055) / 1.055, 2.4);
    };
    return 0.2126 * channel(r) + 0.7152 * channel(g) + 0.0722 * channel(b);
  };
  const contrast = (a, b) => {
    const [l1, l2] = [luminance(a), luminance(b)].sort((x, y) => y - x);
    return (l1 + 0.05) / (l2 + 0.05);
  };
`;

const screens = [
  ["library", "/", null],
  ["study", "/deck/seed_deck", null],
  ["create", "/create", null],
  ["homework", "/homework", null],
  ["chat", "/chat", null],
  ["stats", "/stats", null],
  ["exam", "/exam", null],
  ["settings", "/", "settings"],
];

for (const [label, path, mode] of screens) {
  if (filter && !label.includes(filter)) continue;
  for (const theme of ["dark", "light"]) {
    const { context, page } = await makePage(browser, { width: 390, height: 844, deviceScaleFactor: 1 });
    await seed(page, { decks: [DECK], theme });
    await page.goto(`${BASE}${path}`, { waitUntil: "networkidle" });
    await page.waitForTimeout(1000);
    if (mode === "settings") {
      await page.locator("nav.tabbar").getByRole("button").click();
      await page.getByRole("dialog").waitFor({ timeout: 6000 });
      await page.waitForTimeout(700);
    }

    // Every text-bearing element with a visible box, small enough to sample.
    // Content behind an open sheet is dimmed on purpose and not readable, and
    // disabled controls are exempt from 1.4.3 — both are skipped.
    const targets = await page.evaluate(() => {
      const out = [];
      const dialog = document.querySelector('[role="dialog"]');
      const root = dialog ?? document;
      for (const element of root.querySelectorAll("p, span, li, h1, h2, h3, button, a, label, dt, dd")) {
        if (element.closest("[disabled]") || element.closest('[aria-disabled="true"]')) continue;
        const text = (element.textContent ?? "").trim();
        if (text.length < 2) continue;
        if (element.children.length > 0 && [...element.children].some((child) => (child.textContent ?? "").trim().length > 0)) continue;
        const style = getComputedStyle(element);
        if (style.visibility === "hidden" || style.display === "none" || Number(style.opacity) < 0.5) continue;
        const box = element.getBoundingClientRect();
        if (box.width < 8 || box.height < 8 || box.bottom < 0 || box.top > window.innerHeight) continue;
        out.push({
          id: out.length,
          text: text.slice(0, 40),
          color: style.color,
          fontSize: Number.parseFloat(style.fontSize),
          fontWeight: Number(style.fontWeight),
          box: { x: box.x, y: box.y, width: box.width, height: box.height },
        });
      }
      return out;
    });

    const screenshot = await page.screenshot({ type: "png", scale: "css" });
    const dataUrl = `data:image/png;base64,${screenshot.toString("base64")}`;
    const report = await page.evaluate(
      async ({ targets, dataUrl, luminanceSource }) => {
        const image = await new Promise((resolve, reject) => {
          const img = new Image();
          img.onload = () => resolve(img);
          img.onerror = reject;
          img.src = dataUrl;
        });
        const canvas = document.createElement("canvas");
        canvas.width = image.width;
        canvas.height = image.height;
        const ctx = canvas.getContext("2d");
        ctx.drawImage(image, 0, 0);
        const full = ctx.getImageData(0, 0, canvas.width, canvas.height).data;
        const { contrast } = new Function(`${luminanceSource} return { contrast };`)();
        const parseColor = (value) => {
          const match = /rgba?\(([^)]+)\)/.exec(value);
          if (!match) return null;
          const parts = match[1].split(",").map((part) => Number.parseFloat(part));
          return [parts[0], parts[1], parts[2], parts[3] ?? 1];
        };
        const results = [];
        for (const target of targets) {
          const text = parseColor(target.color);
          if (!text) continue;
          // Sample a slightly larger box and ignore pixels close to the text
          // colour: those are the glyphs themselves, not the background.
          const x0 = Math.max(0, Math.floor(target.box.x) - 2);
          const y0 = Math.max(0, Math.floor(target.box.y) - 2);
          const x1 = Math.min(canvas.width, Math.ceil(target.box.x + target.box.width) + 2);
          const y1 = Math.min(canvas.height, Math.ceil(target.box.y + target.box.height) + 2);
          if (x1 - x0 < 4 || y1 - y0 < 4) continue;
          const counts = new Map();
          let sampled = 0;
          for (let y = y0; y < y1; y += 1) {
            for (let x = x0; x < x1; x += 1) {
              const index = (y * canvas.width + x) * 4;
              const pixel = [full[index], full[index + 1], full[index + 2]];
              const distance = Math.max(
                Math.abs(pixel[0] - text[0]),
                Math.abs(pixel[1] - text[1]),
                Math.abs(pixel[2] - text[2]),
              );
              if (distance <= 24) continue; // glyph pixel (or its antialiasing)
              const key = `${pixel[0]},${pixel[1]},${pixel[2]}`;
              counts.set(key, (counts.get(key) ?? 0) + 1);
              sampled += 1;
            }
          }
          if (sampled < 12) continue; // all glyphs: nothing to measure against
          let best = null;
          for (const [key, count] of counts) if (!best || count > best.count) best = { key, count };
          const background = best.key.split(",").map(Number);
          const ratio = contrast(text, background);
          const large = target.fontSize >= 24 || (target.fontSize >= 18.66 && Number(target.fontWeight) >= 700);
          const minimum = large ? 3 : 4.5;
          if (ratio < minimum) {
            results.push({ text: target.text, ratio: Number(ratio.toFixed(2)), minimum, color: target.color, background: best.key });
          }
        }
        return results;
      },
      { targets, dataUrl, luminanceSource: LUMINANCE },
    );

    if (report.length > 0) {
      console.log(`\n[${theme}] ${label} — ${report.length} below minimum`);
      for (const row of report) {
        console.log(`  ${row.ratio}:1 (needs ${row.minimum}) "${row.text}" — ${row.color} on rgb(${row.background})`);
        failures.push({ theme, label, ...row });
      }
    }
    await context.close();
  }
}

console.log(`\ncontrast scan done — ${failures.length} below-minimum findings`);
await browser.close();