const crypto = require('crypto');

class SuperPageCache {
  constructor() {
    this.cache = new Map(); // path -> { body, contentType, etag, createdAt }
    this.ttlMs = 10 * 60 * 1000; // 10 minutes default memory cache
  }

  middleware() {
    return (req, res, next) => {
      // Only cache GET requests that are not admin, guanli, or API routes
      if (req.method !== 'GET' || req.path.startsWith('/guanli') || req.path.startsWith('/admin') || req.path.startsWith('/api')) {
        return next();
      }

      const cacheKey = req.originalUrl || req.url;
      const cached = this.cache.get(cacheKey);

      if (cached && (Date.now() - cached.createdAt < this.ttlMs)) {
        // Check conditional ETag
        if (req.headers['if-none-match'] === cached.etag) {
          res.setHeader('X-Cache', 'HIT-304');
          return res.status(304).end();
        }

        res.setHeader('X-Cache', 'HIT');
        res.setHeader('ETag', cached.etag);
        res.setHeader('Content-Type', cached.contentType || 'text/html; charset=utf-8');
        res.setHeader('Cache-Control', 'no-cache, must-revalidate');
        return res.send(cached.body);
      }

      // Intercept res.send to populate cache
      const originalSend = res.send.bind(res);
      res.send = (body) => {
        if (res.statusCode === 200 && typeof body === 'string') {
          const etag = `W/"${crypto.createHash('md5').update(body).digest('hex').slice(0, 16)}"`;
          this.cache.set(cacheKey, {
            body,
            contentType: res.getHeader('Content-Type') || 'text/html; charset=utf-8',
            etag,
            createdAt: Date.now()
          });
          res.setHeader('X-Cache', 'MISS');
          res.setHeader('ETag', etag);
          res.setHeader('Cache-Control', 'no-cache, must-revalidate');
        }
        return originalSend(body);
      };

      next();
    };
  }

  clear() {
    const size = this.cache.size;
    this.cache.clear();
    console.log(`[SuperPageCache] Flushed ${size} cached pages.`);
  }

  invalidate(urlPattern) {
    for (const key of this.cache.keys()) {
      if (key.includes(urlPattern)) {
        this.cache.delete(key);
      }
    }
  }
}

module.exports = new SuperPageCache();