import { createHash } from 'node:crypto'
import { existsSync, mkdirSync } from 'node:fs'
import { writeFile } from 'node:fs/promises'
import path from 'node:path'

const EXT_BY_TYPE: Record<string, string> = {
  'image/jpeg': '.jpg',
  'image/png': '.png',
  'image/webp': '.webp',
  'image/gif': '.gif',
}

/**
 * Downloads `url` into `artworkDir` keyed by its sha256 hash. Returns the
 * stored file name (e.g. `abc123….jpg`) or null when the url is empty or the
 * download fails — artwork caching is best-effort and must never break adds.
 */
export async function cacheArtwork(
  artworkDir: string,
  url: string,
  fetchImpl: typeof fetch = fetch
): Promise<string | null> {
  if (!url) return null
  const key = createHash('sha256').update(url).digest('hex')
  mkdirSync(artworkDir, { recursive: true })
  for (const ext of Object.values(EXT_BY_TYPE)) {
    if (existsSync(path.join(artworkDir, key + ext))) return key + ext
  }
  let res: Response
  try {
    res = await fetchImpl(url)
  } catch {
    return null
  }
  if (!res.ok) return null
  const type = (res.headers.get('content-type') ?? '').split(';')[0]?.trim() ?? ''
  const ext = EXT_BY_TYPE[type] ?? '.jpg'
  const buf = Buffer.from(await res.arrayBuffer())
  await writeFile(path.join(artworkDir, key + ext), buf)
  return key + ext
}