interface Bucket {
  count: number
  resetAt: number
}

/**
 * Minimal fixed-window limiter for the public lead endpoint. In-memory on
 * purpose: a single landing page behind one Node process does not warrant a
 * shared store, and losing the counters on restart is harmless.
 */
export function createRateLimiter(options: { limit: number; windowMs: number }) {
  const buckets = new Map<string, Bucket>()

  return function check(key: string): { allowed: boolean; retryAfterSeconds: number } {
    const now = Date.now()

    if (buckets.size > 5000) {
      for (const [k, bucket] of buckets) if (bucket.resetAt <= now) buckets.delete(k)
    }

    const bucket = buckets.get(key)
    if (!bucket || bucket.resetAt <= now) {
      buckets.set(key, { count: 1, resetAt: now + options.windowMs })
      return { allowed: true, retryAfterSeconds: 0 }
    }

    bucket.count += 1
    return {
      allowed: bucket.count <= options.limit,
      retryAfterSeconds: Math.ceil((bucket.resetAt - now) / 1000),
    }
  }
}