const { Readable } = require('stream');
const { pipeline } = require('stream/promises');
const { Agent } = require('undici');

const CONNECT_TIMEOUT_MS = 30_000;
const MAX_ATTEMPTS = 3;
const RETRY_DELAYS_MS = [300, 800];

const videoProxyAgent = new Agent({
  connect: {
    timeout: CONNECT_TIMEOUT_MS
  }
});

const PASSTHROUGH_HEADERS = [
  'content-type',
  'content-length',
  'content-range',
  'accept-ranges',
  'etag',
  'last-modified',
  'cache-control'
];

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

function networkErrorCode(error) {
  return error?.cause?.code || error?.code || '';
}

function isRetryableNetworkError(error) {
  return [
    'UND_ERR_CONNECT_TIMEOUT',
    'UND_ERR_SOCKET',
    'ECONNRESET',
    'ETIMEDOUT',
    'ENETUNREACH',
    'EHOSTUNREACH'
  ].includes(networkErrorCode(error));
}

async function fetchVideoWithRetry(url, init, deps) {
  const fetchImpl = deps.fetchImpl || fetch;
  const maxAttempts = deps.maxAttempts || MAX_ATTEMPTS;
  let lastError = null;

  for (let attempt = 1; attempt <= maxAttempts; attempt += 1) {
    try {
      return await fetchImpl(url, init);
    } catch (error) {
      lastError = error;
      if (!isRetryableNetworkError(error) || attempt >= maxAttempts || init.signal?.aborted) {
        throw error;
      }

      console.warn(
        `[video-proxy] connect attempt ${attempt}/${maxAttempts} failed: ${error.message}; cause=${networkErrorCode(error)}`
      );
      await (deps.sleep || sleep)(RETRY_DELAYS_MS[Math.min(attempt - 1, RETRY_DELAYS_MS.length - 1)]);
    }
  }

  throw lastError || new Error('视频代理连接失败');
}

function registerVideoProxyRoutes(app, deps) {
  app.get('/api/video-proxy', async (req, res) => {
    const { url, filename = 'douyin-video.mp4', download } = req.query;

    if (!url || typeof url !== 'string') {
      return res.status(400).json({ error: '缺少 url 参数' });
    }

    if (!deps.isSafeRemoteUrl(url)) {
      return res.status(400).json({ error: '无效的视频地址' });
    }

    const abortController = new AbortController();
    const abortUpstream = () => {
      if (!res.writableEnded) abortController.abort();
    };
    res.once('close', abortUpstream);

    try {
      const upstreamHeaders = {
        'Accept': req.headers.accept || '*/*',
        'User-Agent': req.headers['user-agent'] || 'Mozilla/5.0',
        'Referer': 'https://www.douyin.com/',
        'Origin': 'https://www.douyin.com'
      };

      if (req.headers.range) {
        upstreamHeaders.Range = req.headers.range;
      }

      const response = await fetchVideoWithRetry(url, {
        method: 'GET',
        headers: upstreamHeaders,
        redirect: 'follow',
        dispatcher: deps.dispatcher || videoProxyAgent,
        signal: abortController.signal
      }, deps);

      if (!response.ok && response.status !== 206) {
        const errorText = await response.text().catch(() => '');
        return res.status(response.status).json({
          error: '远程视频请求失败',
          status: response.status,
          detail: errorText
        });
      }

      res.status(response.status);
      for (const headerName of PASSTHROUGH_HEADERS) {
        const value = response.headers.get(headerName);
        if (value) res.setHeader(headerName, value);
      }

      if (!response.headers.get('content-type')) {
        res.setHeader('Content-Type', 'video/mp4');
      }

      res.setHeader(
        'Content-Disposition',
        download === '1'
          ? `attachment; filename*=UTF-8''${encodeURIComponent(filename)}`
          : `inline; filename*=UTF-8''${encodeURIComponent(filename)}`
      );

      if (!response.body) {
        return res.end();
      }

      await pipeline(Readable.fromWeb(response.body), res);
    } catch (error) {
      if (abortController.signal.aborted && res.destroyed) {
        return;
      }

      const detail = `${error.message}${networkErrorCode(error) ? `; cause=${networkErrorCode(error)}` : ''}`;
      console.error('[video-proxy] request failed:', detail);

      if (!res.headersSent) {
        res.status(500).json({ error: `视频代理失败: ${detail}` });
      } else if (!res.destroyed) {
        res.destroy();
      }
    } finally {
      res.off('close', abortUpstream);
    }
  });
}

module.exports = {
  registerVideoProxyRoutes,
  fetchVideoWithRetry,
  isRetryableNetworkError
};