workspace-v1/shared/libs/rate-limiting/_reference/rate-limiter.service.reference.ts

/**
 * RATE LIMITER SERVICE - REFERENCE IMPLEMENTATION
 *
 * @description Servicio de rate limiting para proteger endpoints.
 * Implementación in-memory simple con soporte para diferentes estrategias.
 *
 * @usage
 * ```typescript
 * // En middleware o guard
 * const limiter = getRateLimiter({ windowMs: 60000, max: 100 });
 * if (limiter.isRateLimited(req.ip)) {
 *   throw new TooManyRequestsException();
 * }
 * ```
 *
 * @origin gamilit/apps/backend/src/shared/services/rate-limiter.service.ts
 */

/**
 * Configuración del rate limiter
 */
export interface RateLimitConfig {
  /** Ventana de tiempo en milisegundos */
  windowMs: number;
  /** Máximo de requests por ventana */
  max: number;
  /** Mensaje de error personalizado */
  message?: string;
  /** Función para generar key (default: IP) */
  keyGenerator?: (req: any) => string;
}

/**
 * Estado interno de un cliente
 */
interface ClientState {
  count: number;
  resetTime: number;
}

/**
 * Rate Limiter Factory
 *
 * @param config - Configuración del limiter
 * @returns Instancia del rate limiter
 */
export function getRateLimiter(config: RateLimitConfig): RateLimiter {
  const clients = new Map<string, ClientState>();

  // Limpieza periódica de entradas expiradas
  const cleanup = setInterval(() => {
    const now = Date.now();
    for (const [key, state] of clients.entries()) {
      if (state.resetTime <= now) {
        clients.delete(key);
      }
    }
  }, config.windowMs);

  return {
    /**
     * Verificar si un cliente está rate limited
     */
    check(key: string): RateLimitResult {
      const now = Date.now();
      const state = clients.get(key);

      // Cliente nuevo o ventana expirada
      if (!state || state.resetTime <= now) {
        clients.set(key, {
          count: 1,
          resetTime: now + config.windowMs,
        });
        return {
          limited: false,
          remaining: config.max - 1,
          resetTime: now + config.windowMs,
        };
      }

      // Incrementar contador
      state.count++;

      // Verificar límite
      if (state.count > config.max) {
        return {
          limited: true,
          remaining: 0,
          resetTime: state.resetTime,
          retryAfter: Math.ceil((state.resetTime - now) / 1000),
        };
      }

      return {
        limited: false,
        remaining: config.max - state.count,
        resetTime: state.resetTime,
      };
    },

    /**
     * Resetear contador de un cliente
     */
    reset(key: string): void {
      clients.delete(key);
    },

    /**
     * Limpiar todos los contadores
     */
    clear(): void {
      clients.clear();
    },

    /**
     * Destruir el limiter (detener cleanup)
     */
    destroy(): void {
      clearInterval(cleanup);
      clients.clear();
    },
  };
}

/**
 * Interfaz del rate limiter
 */
export interface RateLimiter {
  check(key: string): RateLimitResult;
  reset(key: string): void;
  clear(): void;
  destroy(): void;
}

/**
 * Resultado de verificación
 */
export interface RateLimitResult {
  limited: boolean;
  remaining: number;
  resetTime: number;
  retryAfter?: number;
}

/**
 * Middleware para Express/NestJS
 */
export function rateLimitMiddleware(config: RateLimitConfig) {
  const limiter = getRateLimiter(config);
  const keyGenerator = config.keyGenerator || ((req) => req.ip || 'unknown');

  return (req: any, res: any, next: () => void) => {
    const key = keyGenerator(req);
    const result = limiter.check(key);

    // Agregar headers informativos
    res.setHeader('X-RateLimit-Limit', config.max);
    res.setHeader('X-RateLimit-Remaining', result.remaining);
    res.setHeader('X-RateLimit-Reset', result.resetTime);

    if (result.limited) {
      res.setHeader('Retry-After', result.retryAfter);
      res.status(429).json({
        statusCode: 429,
        message: config.message || 'Too many requests',
        retryAfter: result.retryAfter,
      });
      return;
    }

    next();
  };
}

/**
 * Error de rate limit
 */
export class TooManyRequestsError extends Error {
  public readonly statusCode = 429;
  public readonly retryAfter: number;

  constructor(retryAfter: number, message?: string) {
    super(message || 'Too many requests');
    this.retryAfter = retryAfter;
  }
}