import { promises as fs } from 'fs'
import path from 'path'

const HERO_ROOT_CANDIDATES = [
  path.join(process.cwd(), 'public', 'images', 'hero'),
  path.join(process.cwd(), '.output', 'public', 'images', 'hero'),
  path.join(process.cwd(), '..', 'public', 'images', 'hero'),
  path.join(process.cwd(), '..', '.output', 'public', 'images', 'hero')
]

const FALLBACK_FILE_CANDIDATES = [
  'hero_fallback.webp',
  'hero_fallback.jpg',
  'hero_fallback.jpeg',
  'hero_fallback.png'
]

async function findExistingDir(paths) {
  for (const candidate of paths) {
    try {
      const stats = await fs.stat(candidate)
      if (stats.isDirectory()) return candidate
    } catch {
      // ignore
    }
  }
  return null
}

async function fileExists(filePath) {
  try {
    const stats = await fs.stat(filePath)
    return stats.isFile()
  } catch {
    return false
  }
}

function isAllowedVariantKey(key) {
  return /^[A-Za-z0-9_-]+$/.test(key)
}

function appendPathSegment(rootDir, segment) {
  if (!isAllowedVariantKey(segment)) return null
  return `${rootDir}${path.sep}${segment}`
}

async function listHeroVariants(heroRoot) {
  const dirEntries = await fs.readdir(heroRoot, { withFileTypes: true })
  const variants = []

  for (const entry of dirEntries) {
    if (!entry.isDirectory()) continue

    const key = entry.name
    if (!isAllowedVariantKey(key)) continue

    const variantDir = appendPathSegment(heroRoot, key)
    if (!variantDir) continue

    const mobileFile = 'hero_960.webp'
    const desktopFile = 'hero_1600.webp'

    const mobilePath = `${variantDir}${path.sep}${mobileFile}`
    const desktopPath = `${variantDir}${path.sep}${desktopFile}`
    if (!mobilePath || !desktopPath) continue

    if (!(await fileExists(mobilePath)) || !(await fileExists(desktopPath))) {
      continue
    }

    let fallbackFile = desktopFile
    for (const candidate of FALLBACK_FILE_CANDIDATES) {
      const fallbackPath = `${variantDir}${path.sep}${candidate}`
      if (fallbackPath && await fileExists(fallbackPath)) {
        fallbackFile = candidate
        break
      }
    }

    variants.push({
      key,
      mobileWebp: `/images/hero/${key}/${mobileFile}`,
      desktopWebp: `/images/hero/${key}/${desktopFile}`,
      fallback: `/images/hero/${key}/${fallbackFile}`
    })
  }

  return variants.sort((a, b) => a.key.localeCompare(b.key, 'de'))
}

export default defineEventHandler(async (event) => {
  const heroRoot = await findExistingDir(HERO_ROOT_CANDIDATES)
  if (!heroRoot) {
    return { variants: [] }
  }

  const variants = await listHeroVariants(heroRoot)
  setHeader(event, 'Cache-Control', 'public, max-age=300, stale-while-revalidate=600')

  return { variants }
})