object-cache.ts

interface Cache<T> {
  get: (id: string) => T | null;
  set: (id: string, item: T) => void;
  invalidate: (id: string) => void;
};
  
interface CacheEntry<T> {
  // Unix timestamp Math.floor(new Date() / 1000)
  cachedAt: number;
  item: T;
};
  
interface CacheMap<T> {
  [key: string]: CacheEntry<T>
};

interface CacheOptions {
  // In seconds
  TTL: number
};

const createCache<T> = ({ TTL }: CacheOptions): Cache<T> => {
  return {
    _cache: CacheMap<T> = {},
    get: function(id:string) {
      const entry = this._cache[id];
      if (!entry) {
        return null;
      }
      const now = Math.floor(new Date() / 1000);
      if (now - entry.cachedAt > TTL) {
        this.invalidate(id);
        return null;
      }
      return entry.item;
    },
    invalidate(id: string) {
      if (this._cache[id]) {
        delete this._cache[id];
      }
    },
    set(id: string, item: T) {
      const now = Math.floor(new Date() / 1000);
      this._cache[id] = {
        cachedAt: now,
        item
      }
    }
  }
};