const { rateLimit } = require('express-rate-limit');

const { logger } = require('../utils/logger');

function parsePositiveInteger(value, fallback) {
  const parsed = Number(value);
  return Number.isSafeInteger(parsed) && parsed > 0 ? parsed : fallback;
}

function createGlobalApiLimiter(options = {}) {
  const windowMs = parsePositiveInteger(options.windowMs ?? process.env.API_RATE_LIMIT_WINDOW_MS, 60_000);
  const limit = parsePositiveInteger(options.limit ?? process.env.API_RATE_LIMIT_MAX, 600);

  return rateLimit({
    windowMs,
    limit,
    standardHeaders: 'draft-8',
    legacyHeaders: false,
    skip: (req) => req.method === 'OPTIONS' || req.path === '/health',
    handler: (req, res) => {
      (req.log || logger).warn({ method: req.method, path: req.path }, 'global API rate limit exceeded');
      res.status(429).json({
        success: false,
        message: '请求过于频繁，请稍后再试',
        requestId: req.id
      });
    }
  });
}

class RateLimiter {
  constructor(options = {}) {
    this.maxAttempts = options.maxAttempts || 5;
    this.windowMs = options.windowMs || 15 * 60 * 1000;
    this.blockDuration = options.blockDuration || 30 * 60 * 1000;
    this.attempts = new Map();
    this.blockedKeys = new Map();
    this.cleanupInterval = setInterval(() => this.cleanup(), 5 * 60 * 1000);
    this.cleanupInterval.unref?.();
  }

  getClientKey(req) {
    return req.ip || req.socket?.remoteAddress || 'unknown';
  }

  isBlocked(key) {
    const blockInfo = this.blockedKeys.get(key);
    if (!blockInfo) return false;

    if (Date.now() > blockInfo.expiresAt) {
      this.blockedKeys.delete(key);
      this.attempts.delete(key);
      return false;
    }
    return true;
  }

  recordFailure(key) {
    const now = Date.now();
    if (this.isBlocked(key)) {
      const blockInfo = this.blockedKeys.get(key);
      return {
        blocked: true,
        remainingAttempts: 0,
        resetTime: blockInfo.expiresAt,
        waitMinutes: Math.ceil((blockInfo.expiresAt - now) / 60_000),
        needCaptcha: true
      };
    }

    let attemptInfo = this.attempts.get(key);
    if (!attemptInfo || now > attemptInfo.windowEnd) {
      attemptInfo = { count: 0, windowEnd: now + this.windowMs, firstAttempt: now };
    }

    attemptInfo.count += 1;
    this.attempts.set(key, attemptInfo);
    if (attemptInfo.count >= this.maxAttempts) {
      const blockExpiresAt = now + this.blockDuration;
      this.blockedKeys.set(key, { expiresAt: blockExpiresAt, blockedAt: now });
      logger.warn({ key, attempts: attemptInfo.count, blockDuration: this.blockDuration }, 'failure limiter blocked key');
      return {
        blocked: true,
        remainingAttempts: 0,
        resetTime: blockExpiresAt,
        waitMinutes: Math.ceil(this.blockDuration / 60_000),
        needCaptcha: true
      };
    }

    return {
      blocked: false,
      remainingAttempts: this.maxAttempts - attemptInfo.count,
      resetTime: attemptInfo.windowEnd,
      waitMinutes: 0,
      needCaptcha: attemptInfo.count >= 2
    };
  }

  getFailureCount(key) {
    const attemptInfo = this.attempts.get(key);
    if (!attemptInfo || Date.now() > attemptInfo.windowEnd) return 0;
    return attemptInfo.count;
  }

  recordSuccess(key) {
    this.attempts.delete(key);
    this.blockedKeys.delete(key);
  }

  cleanup() {
    const now = Date.now();
    let cleanedAttempts = 0;
    let cleanedBlocks = 0;

    for (const [key, info] of this.attempts.entries()) {
      if (now > info.windowEnd) {
        this.attempts.delete(key);
        cleanedAttempts += 1;
      }
    }
    for (const [key, info] of this.blockedKeys.entries()) {
      if (now > info.expiresAt) {
        this.blockedKeys.delete(key);
        cleanedBlocks += 1;
      }
    }

    if (cleanedAttempts || cleanedBlocks) {
      logger.info({ cleanedAttempts, cleanedBlocks }, 'failure limiter cleanup completed');
    }
  }

  getStats() {
    return {
      activeAttempts: this.attempts.size,
      blockedKeys: this.blockedKeys.size
    };
  }

  destroy() {
    if (this.cleanupInterval) clearInterval(this.cleanupInterval);
  }
}

module.exports = {
  RateLimiter,
  createGlobalApiLimiter
};