import express from 'express';
import fetch from 'node-fetch';
import { URL } from 'url';

const app = express();
const port = 3000;

// 允许跨域请求
app.use((req, res, next) => {
  res.header('Access-Control-Allow-Origin', '*');
  res.header('Access-Control-Allow-Methods', 'GET, HEAD, OPTIONS');
  res.header('Access-Control-Allow-Headers', 'Range');
  next();
});

// 通用代理路由
app.get('/proxy', async (req, res) => {
  console.log('Received Range header:', req.headers.range);
  // 获取目标 URL
  const targetUrl = req.query.url;
  console.log('Fetching data from:', targetUrl);
  if (!targetUrl) {
    return res.status(400).json({ error: 'URL parameter is required' });
  }

  try {
    // 设置请求头
    const headers = {
      'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36'
    };
    if (req.headers.range) {
      headers['Range'] = req.headers.range; // 转发 Range 请求头，支持视频分段加载
    }

    // 向目标 URL 发起请求
    const response = await fetch(targetUrl, { headers });

    // 检查响应状态
    if (!response.ok) {
      return res.status(response.status).json({ 
        error: `Failed to fetch: ${response.statusText}`,
        status: response.status 
      });
    }

    // 设置响应头
    response.headers.forEach((value, key) => {
      // 跳过一些可能导致问题的头信息
      if (key.toLowerCase() !== 'content-encoding' && 
          key.toLowerCase() !== 'transfer-encoding' &&
          key.toLowerCase() !== 'connection') {
        res.setHeader(key, value);
      }
    });

    // 特殊处理 Transfer-Encoding 和 Content-Length
    if (response.headers.get('transfer-encoding') === 'chunked') {
      res.removeHeader('Content-Length');
    }

    // 将响应体直接流式传输给客户端
    if (response.body) {
      response.body.pipe(res, { end: true });

      // 错误处理
      response.body.on('error', (err) => {
        console.error('Error during data transfer:', err);
        if (!res.headersSent) {
          res.status(500).json({ error: 'Error during data transfer' });
        }
      });
    } else {
      res.status(500).json({ error: 'No response body' });
    }
  } catch (error) {
    console.error('Error fetching data:', error);
    
    // 根据错误类型返回更具体的错误信息
    let errorMessage = 'Error fetching data';
    let statusCode = 500;
    let hostname = '';
    
    try {
      hostname = new URL(targetUrl).hostname;
    } catch (e) {
      hostname = 'unknown';
    }
    
    if (error.code === 'ENOTFOUND') {
      errorMessage = `DNS解析失败：无法解析域名 "${hostname}"。请检查URL是否正确，或网络连接是否正常。`;
      statusCode = 502;
    } else if (error.code === 'ECONNREFUSED') {
      errorMessage = `连接被拒绝：无法连接到目标服务器 "${hostname}"。`;
      statusCode = 502;
    } else if (error.code === 'ETIMEDOUT') {
      errorMessage = `请求超时：目标服务器 "${hostname}" 响应时间过长。`;
      statusCode = 504;
    }
    
    if (!res.headersSent) {
      res.status(statusCode).json({ 
        error: errorMessage,
        code: error.code,
        targetUrl: targetUrl 
      });
    }
  }
});

app.listen(port, () => {
  console.log(`Proxy server running at http://localhost:${port}`);
});