const express = require('express');
const axios = require('axios');
const fs = require('fs');
const path = require('path');
const crypto = require('crypto');
const net = require('net');

require('dotenv').config();
const app = express();
const PORT = Number(process.env.PORT) || 11489;
const UPSTREAM_HOST = 'https://s0.wp.com';
const CACHE_DIR = path.join(process.cwd(), 'cache');

fs.mkdirSync(CACHE_DIR, { recursive: true });

/**
 * 计算 SHA1 哈希
 * @param {string} input 
 * @returns {string}
 */
function sha1(input) {
  return crypto.createHash('sha1').update(input).digest('hex');
}

/**
 * 获取缓存文件路径
 * @param {string} key 
 * @returns {{data: string, meta: string}}
 */
function getCachePaths(key) {
  return {
    data: path.join(CACHE_DIR, `${key}.data`),
    meta: path.join(CACHE_DIR, `${key}.json`),
  };
}

/**
 * 验证响应是否为有效的图片
 * @param {number} status 
 * @param {object} headers 
 * @param {any} data 
 * @returns {boolean}
 */
function isValidImageResponse(status, headers, data) {
  const ct = (headers['content-type'] || '').toLowerCase();
  const lenHeader = headers['content-length'];
  const len = Array.isArray(data) ? data.length : (data?.byteLength || 0);
  const hasPositiveLength = (lenHeader ? parseInt(lenHeader, 10) > 0 : len > 0);

  // 过滤掉 GIF 图片 (通常是 mShots 的 "Generating" 占位图，约 9KB)
  // 我们不缓存这些图片，以便下次请求时能再次尝试获取真实截图
  if (ct.includes('image/gif') && len < 15000) {
    return false;
  }

  return status === 200 && ct.startsWith('image/') && hasPositiveLength;
}

/**
 * 检查主机是否开放 443 端口 (简单的 SSL 判断)
 * @param {string} host 
 * @returns {Promise<boolean>}
 */
function checkPort443(host) {
  return new Promise(resolve => {
    // 默认超时 1.5 秒，避免阻塞太久
    const socket = net.connect(443, host);
    socket.setTimeout(1500);
    socket.on('connect', () => {
      socket.end();
      resolve(true);
    });
    socket.on('error', () => {
      resolve(false);
    });
    socket.on('timeout', () => {
      socket.destroy();
      resolve(false);
    });
  });
}

/**
 * 解析目标 URL，支持自动补全协议
 * @param {string} rawPath 
 * @returns {Promise<string>}
 */
async function resolveTargetUrl(rawPath) {
  // 去除开头的 /
  let target = rawPath.startsWith('/') ? rawPath.slice(1) : rawPath;

  // 如果已经包含协议，直接返回
  if (target.startsWith('http://') || target.startsWith('https://')) {
    return target;
  }

  // 提取主机名
  let host = target.split('/')[0].split('?')[0];
  // 去除端口号（如果存在）
  const colonIndex = host.indexOf(':');
  if (colonIndex !== -1) {
    host = host.substring(0, colonIndex);
  }

  // 尝试检测 SSL
  const isHttps = await checkPort443(host);
  if (!isHttps) {
    console.log(`[protocol-detect] ${host} : 443 port closed or timeout, falling back to HTTP.`);
  }
  return isHttps ? `https://${target}` : `http://${target}`;
}

/**
 * 请求上游并处理重试
 * @param {string} upstreamUrl 
 * @param {number} tries 
 * @returns {Promise<any>}
 */
async function fetchUpstreamWithRetry(upstreamUrl, tries = 2) {
  let lastErr = null;
  for (let i = 0; i < tries; i++) {
    try {
      return await axios.get(upstreamUrl, {
        responseType: 'arraybuffer',
        headers: {
          'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120 Safari/537.36',
          'Accept': 'image/avif,image/webp,image/apng,image/*;q=0.8,*/*;q=0.5',
          'Host': 's0.wp.com',
        },
        maxRedirects: 5,
        timeout: 20000,
        // 禁用代理环境变量的干扰
        proxy: false,
        // 明确允许非 2xx 也返回给上层判断
        validateStatus: () => true,
      });
    } catch (err) {
      lastErr = err;
      console.error(`[upstream-error] try=${i + 1} url=${upstreamUrl} msg=${err.message}`);
      // 简单退避
      await new Promise(r => setTimeout(r, 300));
    }
  }
  if (lastErr) throw lastErr;
}

/**
 * 核心处理逻辑：检查缓存 -> 回源 -> 写入缓存 -> 返回响应
 * @param {object} res 
 * @param {string} upstreamUrl 
 */
async function handleProxyRequest(res, upstreamUrl) {
  const key = sha1(upstreamUrl);
  const { data: dataPath, meta: metaPath } = getCachePaths(key);

  try {
    // 1. 尝试读取缓存
    if (fs.existsSync(dataPath) && fs.existsSync(metaPath)) {
      try {
        const metaRaw = fs.readFileSync(metaPath, 'utf8');
        const meta = JSON.parse(metaRaw);
        if (meta.contentType && meta.contentType.toLowerCase().startsWith('image/')) {
          res.set('Cache-Control', 'public, max-age=315360000, immutable');
          res.type(meta.contentType);
          const stream = fs.createReadStream(dataPath);
          stream.on('error', () => {
              if (!res.headersSent) res.status(500).send('Cache read error');
          });
          return stream.pipe(res);
        }
      } catch (e) {
        // 缓存元数据损坏，忽略，继续回源
      }
    }

    // 2. 回源请求
    const resp = await fetchUpstreamWithRetry(upstreamUrl);

    // 3. 仅缓存有效图片
    if (isValidImageResponse(resp.status, resp.headers, resp.data)) {
      const contentType = resp.headers['content-type'] || 'image/jpeg';
      const meta = {
        url: upstreamUrl,
        contentType,
        size: resp.data.byteLength,
        createdAt: new Date().toISOString(),
      };
      try {
        fs.writeFileSync(dataPath, resp.data);
        fs.writeFileSync(metaPath, JSON.stringify(meta));
      } catch (e) {
        // 写盘失败也继续返回
      }
      res.type(contentType);
      res.set('Cache-Control', 'public, max-age=315360000, immutable');
      return res.send(resp.data);
    }

    // 4. 非图片或非200：兜底策略
    // 若本地已有有效缓存（可能是旧的但有效），优先返回缓存
    if (fs.existsSync(dataPath) && fs.existsSync(metaPath)) {
      try {
        const metaRaw = fs.readFileSync(metaPath, 'utf8');
        const meta = JSON.parse(metaRaw);
        if (meta.contentType && meta.contentType.toLowerCase().startsWith('image/')) {
          res.set('Cache-Control', 'public, max-age=315360000, immutable');
          res.type(meta.contentType);
          const stream = fs.createReadStream(dataPath);
          stream.on('error', () => {
              if (!res.headersSent) res.status(500).send('Cache read error');
          });
          return stream.pipe(res);
        }
      } catch (_) {}
    }

    // 否则透传上游响应
    res.status(resp.status);
    if (resp.headers['content-type']) res.type(resp.headers['content-type']);
    return res.send(resp.data);

  } catch (err) {
    // 5. 回源彻底失败
    // 若本地有缓存可兜底
    if (fs.existsSync(dataPath) && fs.existsSync(metaPath)) {
      try {
        const metaRaw = fs.readFileSync(metaPath, 'utf8');
        const meta = JSON.parse(metaRaw);
        if (meta.contentType && meta.contentType.toLowerCase().startsWith('image/')) {
          res.set('Cache-Control', 'public, max-age=315360000, immutable');
          res.type(meta.contentType);
          const stream = fs.createReadStream(dataPath);
          stream.on('error', () => {
              if (!res.headersSent) res.status(500).send('Cache read error');
          });
          return stream.pipe(res);
        }
      } catch (_) {}
    }
    console.error(`[upstream-failed] url=${upstreamUrl} err=${err.message}`);
    return res.status(502).type('text/plain').send('Upstream error');
  }
}

// 反代 mShots，路径 /mshots/v1/...
app.use('/mshots/v1', async (req, res) => {
  if (req.method !== 'GET') {
    return res.status(405).type('text/plain').send('Method Not Allowed');
  }
  
  // 这里的 req.originalUrl 包含 /mshots/v1 前缀
  // 我们假设用户可能访问 /mshots/v1/www.baidu.com
  // 需要提取出后面的部分进行解析
  const prefix = '/mshots/v1';
  let pathPart = req.originalUrl;
  if (pathPart.startsWith(prefix)) {
    pathPart = pathPart.slice(prefix.length);
  }
  
  // 解析目标 URL（补全协议）
  const targetUrl = await resolveTargetUrl(pathPart);
  
  // 拼接完整上游 URL
  const upstreamUrl = UPSTREAM_HOST + '/mshots/v1/' + targetUrl;
  
  return handleProxyRequest(res, upstreamUrl);
});

// 根路径处理：/https://example.com 或 /www.baidu.com
app.use(async (req, res) => {
  if (req.method !== 'GET') {
    return res.status(405).type('text/plain').send('Method Not Allowed');
  }
  if (req.path === '/') {
    return res.type('text/plain').send('mShots proxy is running. Try /https://www.baidu.com or /www.baidu.com');
  }

  // 解析目标 URL（补全协议）
  const targetUrl = await resolveTargetUrl(req.originalUrl);
  
  // 拼接完整上游 URL
  const upstreamUrl = UPSTREAM_HOST + '/mshots/v1/' + targetUrl;

  return handleProxyRequest(res, upstreamUrl);
});

// 简单根路由健康检查
// 根路径健康由上面的 app.use 处理

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