// In-memory sliding-window rate limiter.
//
// State is module-scoped: each Next.js runtime (Edge middleware vs Node.js server
// components) gets its own module instance, so buckets are not shared between them.
//
// Redis migration path: replace the `buckets` Map with an upstash/ratelimit or
// ioredis ZADD + ZRANGEBYSCORE approach. The exported function signatures stay the
// same, only the storage layer changes, giving cross-process and cross-runtime
// consistency for multi-replica deployments.

const WINDOW_MS = 60_000; // 1 minute
const LIMIT = 50; // max attempts per window per key
const MAX_KEYS = 10_000; // evict oldest when Map grows beyond this

const buckets = new Map<string, number[]>();

function sweep(key: string, now: number): number[] {
  const fresh = (buckets.get(key) ?? []).filter((t) => now - t < WINDOW_MS);
  buckets.set(key, fresh);
  return fresh;
}

function evictOldest(exclude: string) {
  if (buckets.size < MAX_KEYS) return;
  for (const k of buckets.keys()) {
    if (k !== exclude) {
      buckets.delete(k);
      return;
    }
  }
}

/**
 * Check whether `key` has exceeded the rate limit WITHOUT recording a new attempt.
 * Use this to gate a request before you know whether it will succeed or fail.
 */
export function isRateLimited(key: string): boolean {
  return sweep(key, Date.now()).length >= LIMIT;
}

/**
 * Record one failed attempt for `key`.
 * Successful requests should NOT call this — only failures increment the bucket.
 */
export function recordFailure(key: string): void {
  const now = Date.now();
  const ts = sweep(key, now);
  if (ts.length >= LIMIT) return; // already over limit; don't bother growing the array
  evictOldest(key);
  buckets.set(key, [...ts, now]);
}

/**
 * Check and atomically consume one token for `key`.
 * Returns `true` if the request is allowed; `false` if rate-limited.
 * Used by middleware where every inbound request (success or failure) is counted.
 */
export function consume(key: string): boolean {
  const now = Date.now();
  const ts = sweep(key, now);
  if (ts.length >= LIMIT) return false;
  evictOldest(key);
  buckets.set(key, [...ts, now]);
  return true;
}