import { NextRequest, NextResponse } from 'next/server';

/**
 * Rate limiting configuration
 * Simple in-memory rate limiter for API endpoints
 */
interface RateLimitEntry {
    count: number;
    resetTime: number;
}

const rateLimitMap = new Map<string, RateLimitEntry>();

// Clean up old entries every 5 minutes
setInterval(() => {
    const now = Date.now();
    for (const [key, entry] of rateLimitMap.entries()) {
        if (now > entry.resetTime) {
            rateLimitMap.delete(key);
        }
    }
}, 5 * 60 * 1000);

export interface RateLimitConfig {
    windowMs: number;  // Time window in milliseconds
    maxRequests: number;  // Maximum requests per window
}

/**
 * Rate limiting middleware
 * @param request - The incoming request
 * @param config - Rate limit configuration
 * @returns NextResponse with 429 status if rate limit exceeded, null otherwise
 */
export function rateLimit(
    request: NextRequest,
    config: RateLimitConfig = { windowMs: 60000, maxRequests: 100 }
): NextResponse | null {
    // Get client identifier (IP address or fallback)
    const identifier =
        request.headers.get('x-forwarded-for')?.split(',')[0] ||
        request.headers.get('x-real-ip') ||
        'unknown';

    const now = Date.now();
    const entry = rateLimitMap.get(identifier);

    if (!entry || now > entry.resetTime) {
        // Create new entry or reset expired entry
        rateLimitMap.set(identifier, {
            count: 1,
            resetTime: now + config.windowMs
        });
        return null;
    }

    if (entry.count >= config.maxRequests) {
        const retryAfter = Math.ceil((entry.resetTime - now) / 1000);
        return NextResponse.json(
            { error: 'Too many requests. Please try again later.' },
            {
                status: 429,
                headers: {
                    'Retry-After': retryAfter.toString(),
                    'X-RateLimit-Limit': config.maxRequests.toString(),
                    'X-RateLimit-Remaining': '0',
                    'X-RateLimit-Reset': new Date(entry.resetTime).toISOString()
                }
            }
        );
    }

    // Increment counter
    entry.count++;
    return null;
}