/**
 * Simple in-memory LRU cache for Immich API responses.
 * Avoids hammering the Immich server with identical requests.
 */

interface CacheEntry<T> {
  data: T;
  expiresAt: number;
}

class MemoryCache {
  private store = new Map<string, CacheEntry<unknown>>();
  private maxEntries = 200;

  get<T>(key: string): T | null {
    const entry = this.store.get(key);
    if (!entry) return null;

    if (Date.now() > entry.expiresAt) {
      this.store.delete(key);
      return null;
    }

    // LRU: Move accessed item to the back of the Map (newest)
    this.store.delete(key);
    this.store.set(key, entry);

    return entry.data as T;
  }

  set<T>(key: string, data: T, ttlMs: number): void {
    // If key exists, delete it first to ensure we push it to the back
    if (this.store.has(key)) {
      this.store.delete(key);
    } else if (this.store.size >= this.maxEntries) {
      // Evict oldest entry (first item) if at capacity
      const firstKey = this.store.keys().next().value;
      if (firstKey) this.store.delete(firstKey);
    }

    this.store.set(key, {
      data,
      expiresAt: Date.now() + ttlMs,
    });
  }

  delete(key: string): void {
    this.store.delete(key);
  }

  clear(): void {
    this.store.clear();
  }
}

export const cache = new MemoryCache();