/***********************************************************************************************************************************************************************
 * File Name: rateLimiter.middleware.js
 * Type of Program: Middleware
 * Description: Express-rate-limit configurations for different route tiers.
 *              - globalLimiter      → applied to ALL routes (1000 req / 15 min)
 *              - authLimiter        → applied to login/register (20 req / 15 min)
 *              - otpLimiter         → applied to OTP send/verify (5 req / 15 min)
 *              - sensitiveOpsLimiter → password change, account delete (10 req / hour)
 *              - adminLimiter       → admin routes (200 req / 15 min)
 *
 *              Store selection is driven by CACHE_DRIVER:
 *                redis  → RedisStore (shared across processes; required in production)
 *                memory → in-process MemoryStore (fine for local dev, single process)
 * Author: rgrgogu
 * Date Created: Oct. 6, 2025
 * Date Modified: Jun. 19, 2026
 ***********************************************************************************************************************************************************************
 * HOW TO USE:
 *   const { authLimiter } = require('../middleware/rateLimiter.middleware');
 *   router.post('/login', authLimiter, loginHandler);
 ***********************************************************************************************************************************************************************/
const rateLimit = require('express-rate-limit');
const redisClient = require('../config/redis.config');

const windowMs15 = 15 * 60 * 1000; // 15 minutes

const makeStore = redisClient
  ? (() => {
      const { RedisStore } = require('rate-limit-redis');
      return (prefix) => new RedisStore({
        sendCommand: (...args) => redisClient.sendCommand(args),
        prefix: `rl:${prefix}:`,
      });
    })()
  : () => undefined; // undefined → express-rate-limit uses its default MemoryStore

/** Applied globally in server.js */
const globalLimiter = rateLimit({
  windowMs: windowMs15,
  max: 1000,
  standardHeaders: true,
  legacyHeaders: false,
  store: makeStore('global'),
  message: { status: 'error', message: 'Too many requests, please try again later.' },
});

/** Login & register routes */
const authLimiter = rateLimit({
  windowMs: windowMs15,
  max: 20,
  standardHeaders: true,
  legacyHeaders: false,
  store: makeStore('auth'),
  message: { status: 'error', message: 'Too many auth attempts. Please wait 15 minutes.' },
});

/** OTP send / verify */
const otpLimiter = rateLimit({
  windowMs: windowMs15,
  max: 5,
  standardHeaders: true,
  legacyHeaders: false,
  store: makeStore('otp'),
  message: { status: 'error', message: 'Too many OTP requests. Please wait 15 minutes.' },
});

/**
 * Sensitive write operations — bulk actions, uploads, financial transactions.
 * Keys by authenticated user ID when available, falls back to IP.
 * Keying by IP alone is unfair on shared networks (office NAT, university Wi-Fi)
 * where one user triggering the limit would block everyone behind the same IP.
 */
const sensitiveOpsLimiter = rateLimit({
  windowMs: 60 * 60 * 1000, // 1 hour
  max: 10,
  keyGenerator: (req) => req.user?.user_id?.toString() ?? req.ip,
  standardHeaders: true,
  legacyHeaders: false,
  store: makeStore('sensitive'),
  message: { status: 'error', message: 'Too many sensitive operations. Please wait 1 hour.' },
});

/** Admin routes — tighter than global */
const adminLimiter = rateLimit({
  windowMs: windowMs15,
  max: 200,
  standardHeaders: true,
  legacyHeaders: false,
  store: makeStore('admin'),
  message: { status: 'error', message: 'Too many admin requests. Please wait 15 minutes.' },
});

module.exports = { globalLimiter, authLimiter, otpLimiter, sensitiveOpsLimiter, adminLimiter };