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.`)
}