const lookups = new Map<string, Promise<string | null>>()

async function lookUpCover(isbn: string): Promise<string | null> {
  try {
    const edition = await $fetch<{ covers?: number[] }>(`https://openlibrary.org/isbn/${isbn}.json`)
    const id = edition.covers?.find(id => id > 0)
    return id ? `https://covers.openlibrary.org/b/id/${id}-M.jpg` : null
  } catch {
    return null
  }
}

/**
 * The book's cover: the one saved in the table, or else looked up on Open Library by ISBN
 * and saved to the table so the next visit doesn't have to look it up again.
 */
export function useWishlistCover(book: MaybeRefOrGetter<WishlistBook>) {
  const url = ref<string | null>(toValue(book).cover)
  const loading = ref(!url.value)

  onMounted(async () => {
    if (url.value) return
    const { id, isbn } = toValue(book)
    const digits = isbn.replace(/[^\dX]/gi, '')
    if (!digits) {
      loading.value = false
      return
    }

    if (!lookups.has(digits)) lookups.set(digits, lookUpCover(digits))
    url.value = await lookups.get(digits)!
    loading.value = false

    if (url.value) {
      $fetch(`/api/wishlist/books/${id}/cover`, { method: 'POST', body: { cover: url.value } }).catch(() => {})
    }
  })

  return { url, loading }
}