import { loadSettings } from '../../../utils/appconfig'
import { withSwarm } from '../../../utils/swarm'

const IMAGE_TYPES: Record<string, string> = {
  jpg: 'image/jpeg',
  jpeg: 'image/jpeg',
  png: 'image/png',
  gif: 'image/gif',
  webp: 'image/webp',
  bmp: 'image/bmp',
  avif: 'image/avif'
}

/** 超过这个大小就不做在线预览了，从 swarm 拉一张大图的代价太高 */
const MAX_PREVIEW_BYTES = 12 * 1024 * 1024
/** 单张图片的下载时间上限 */
const DOWNLOAD_TIMEOUT_MS = 25_000

function normPath(value: string): string {
  return value.replace(/\\/g, '/').replace(/^\.\//, '')
}

/**
 * 从 swarm 里只把某一张图片的字节拉下来用于预览。
 * 只下载该文件覆盖到的分片，不落库、不长期占用磁盘。
 */
export default defineEventHandler(async (event) => {
  const infoHash = String(getRouterParam(event, 'infohash') || '').toLowerCase()
  if (!/^[a-f0-9]{40}$/.test(infoHash)) {
    throw createError({ statusCode: 400, statusMessage: 'infoHash 格式不正确' })
  }

  const query = getQuery(event)
  const magnet = String(query.magnet || '')
  const filePath = String(query.path || '')
  if (!/^magnet:\?/i.test(magnet)) {
    throw createError({ statusCode: 400, statusMessage: '缺少可用的磁力链，无法定位做种节点' })
  }
  if (!filePath) {
    throw createError({ statusCode: 400, statusMessage: '缺少 path 参数' })
  }

  const ext = filePath.slice(filePath.lastIndexOf('.') + 1).toLowerCase()
  const mime = IMAGE_TYPES[ext]
  if (!mime) {
    throw createError({ statusCode: 400, statusMessage: '只支持预览图片文件（jpg / png / gif / webp / bmp / avif）' })
  }

  const settings = await loadSettings()
  try {
    const bytes = await withSwarm(infoHash, magnet, settings.metadataTimeout, async (torrent) => {
      const target = (torrent.files || []).find(
        (f: any) => normPath(String(f.path || f.name || '')) === normPath(filePath)
      )
      if (!target) {
        throw createError({ statusCode: 404, statusMessage: '这个种子里没有该文件，文件清单可能已过期' })
      }
      if (target.length > MAX_PREVIEW_BYTES) {
        throw createError({
          statusCode: 413,
          statusMessage: `这张图 ${Math.round(target.length / 1024 / 1024)} MB，超过在线预览上限 ${MAX_PREVIEW_BYTES / 1024 / 1024} MB`
        })
      }
      return Promise.race<ArrayBuffer>([
        target.arrayBuffer(),
        new Promise<never>((_, reject) => {
          setTimeout(
            () => reject(new Error('下载图片超时：暂时没有可用的做种节点，稍后再试')),
            DOWNLOAD_TIMEOUT_MS
          )
        })
      ])
    })

    setHeader(event, 'content-type', mime)
    setHeader(event, 'content-length', String(bytes.byteLength))
    setHeader(
      event,
      'content-disposition',
      `inline; filename="${encodeURIComponent(filePath.slice(filePath.lastIndexOf('/') + 1))}"`
    )
    setHeader(event, 'cache-control', 'private, max-age=3600')
    return Buffer.from(bytes)
  } catch (err) {
    // 把 withSwarm 抛出的原始错误（如 webtorrent 无法加载）转成可读的 HTTP 错误，
    // 避免前端看到 Nitro 的通用 Server Error 页面。
    if (err && typeof err === 'object' && 'statusCode' in err) throw err
    const message = err instanceof Error ? err.message : '从做种节点获取图片失败'
    throw createError({ statusCode: 503, statusMessage: message })
  }
})