import { readdir, readFile, stat } from 'node:fs/promises';
import { join } from 'node:path';

const generatedRoot = '.generated';

const walk = async (directory) => {
  const files = [];
  for (const entry of await readdir(directory, { withFileTypes: true })) {
    const path = join(directory, entry.name);
    if (entry.isDirectory()) files.push(...await walk(path));
    else files.push(path);
  }
  return files;
};

const exists = async (path) => {
  try {
    await stat(path);
    return true;
  } catch {
    return false;
  }
};

const errors = [];
const htmlFiles = (await walk(generatedRoot)).filter((file) => file.endsWith('.html'));
const clientSource = await readFile('src/main.js', 'utf8');
const builtInPrismLanguages = new Set(['markup', 'html', 'xml', 'svg', 'css', 'clike', 'javascript', 'js', 'plain', 'plaintext', 'text', 'txt']);
const prismLanguageAliases = { sh: 'bash', shell: 'bash' };

for (const file of htmlFiles) {
  const html = await readFile(file, 'utf8');
  const ids = [...html.matchAll(/\sid="([^"]+)"/g)].map((match) => match[1]);
  const duplicateIds = ids.filter((id, index) => ids.indexOf(id) !== index);
  if (duplicateIds.length > 0) errors.push(`${file}: duplicate IDs: ${[...new Set(duplicateIds)].join(', ')}`);
  if (!html.includes('<meta name="viewport"')) errors.push(`${file}: missing viewport metadata`);
  if (html.includes('<heading')) errors.push(`${file}: contains a nonstandard <heading> element`);

  for (const [, fragment] of html.matchAll(/href="#([^"]+)"/g)) {
    if (!ids.includes(fragment)) errors.push(`${file}: missing fragment target #${fragment}`);
  }

  for (const [, href] of html.matchAll(/href="(\/[^"]*)"/g)) {
    if (href === '/') continue;
    const pathname = href.split(/[?#]/, 1)[0];
    let target;
    if (pathname.startsWith('/src/')) target = `.${pathname}`;
    else if (pathname.startsWith('/assets/') || pathname === '/favicon.ico') target = `public${pathname}`;
    else target = pathname.endsWith('/')
      ? join(generatedRoot, pathname, 'index.html')
      : join(generatedRoot, pathname);
    if (!await exists(target)) errors.push(`${file}: broken internal link ${href}`);
  }

  for (const [, language] of html.matchAll(/class="language-([\w-]+)"/g)) {
    if (builtInPrismLanguages.has(language)) continue;
    const component = prismLanguageAliases[language] ?? language;
    if (!clientSource.includes(`prism-${component}`)) errors.push(`${file}: Prism grammar is not imported for ${language}`);
  }
}

if (errors.length > 0) {
  console.error(errors.join('\n'));
  process.exitCode = 1;
} else {
  console.log(`Checked ${htmlFiles.length} generated pages.`);
}