interface WindowEntry {
	count: number;
	resetAt: number;
}

const windows = new Map<string, WindowEntry>();

// Purge expired entries every 60s
setInterval(() => {
	const now = Date.now();
	for (const [key, entry] of windows) {
		if (now > entry.resetAt) windows.delete(key);
	}
}, 60_000).unref();

/**
 * Fixed-window rate limiter. Returns null if allowed,
 * or a 429 Response if the limit is exceeded.
 */
export function rateLimit(
	key: string,
	limit: number,
	windowMs: number,
): Response | null {
	const now = Date.now();
	const entry = windows.get(key);
	if (!entry || now > entry.resetAt) {
		windows.set(key, { count: 1, resetAt: now + windowMs });
		return null;
	}
	if (entry.count >= limit) {
		const retryAfter = Math.ceil((entry.resetAt - now) / 1000);
		return new Response("Too many requests", {
			status: 429,
			headers: { "Retry-After": String(retryAfter) },
		});
	}
	entry.count++;
	return null;
}

export function getClientIp(request: Request): string {
	return (
		request.headers.get("cf-connecting-ip") ??
		request.headers.get("x-forwarded-for")?.split(",")[0]?.trim() ??
		"unknown"
	);
}