// server/src/middleware/ipRateLimit.js — 通用 IP 限流（内存版，单进程够用）
// 用法：app.use('/api/ai', ipRateLimit({ windowMs: 60_000, max: 10, name: 'ai' }));
// 命中时返 429 + Retry-After，不写 DB（防撞库那套是 DB 版，这里只防误触/打爆 MySQL）

const buckets = new Map(); // key -> { count, resetAt }

function getKey(req, name) {
    // 用 X-Forwarded-For 第一跳（Vite 代理会塞），fallback 到 socket 地址
    const xff = (req.headers['x-forwarded-for'] || '').split(',')[0]?.trim();
    const ip = xff || req.socket?.remoteAddress || req.ip || '0.0.0.0';
    return `${name}:${ip}`;
}

export function ipRateLimit({ windowMs = 60_000, max = 10, name = 'rl' } = {}) {
    return function (req, res, next) {
        // 定时清理，避免 Map 无限增长
        if (buckets.size > 5000) {
            const now = Date.now();
            for (const [k, v] of buckets) if (v.resetAt < now) buckets.delete(k);
        }
        const key = getKey(req, name);
        const now = Date.now();
        const b = buckets.get(key);
        if (!b || b.resetAt < now) {
            buckets.set(key, { count: 1, resetAt: now + windowMs });
            return next();
        }
        b.count++;
        if (b.count > max) {
            const retryAfter = Math.max(1, Math.ceil((b.resetAt - now) / 1000));
            res.set('Retry-After', String(retryAfter));
            res.set('X-RateLimit-Limit', String(max));
            res.set('X-RateLimit-Remaining', '0');
            res.set('X-RateLimit-Reset', String(Math.ceil(b.resetAt / 1000)));
            return res.status(429).json({
                ok: false,
                error: {
                    code: 'RATE_LIMITED',
                    message: `请求过于频繁，请 ${retryAfter} 秒后再试`,
                    retry_after: retryAfter,
                },
            });
        }
        res.set('X-RateLimit-Limit', String(max));
        res.set('X-RateLimit-Remaining', String(max - b.count));
        next();
    };
}

// 给测试用的清理函数
export function _clearBuckets() { buckets.clear(); }