hometown/app/javascript/mastodon/utils/cache.ts

export interface LimitedCache<CacheKey, CacheValue> {
  has: (key: CacheKey) => boolean;
  get: (key: CacheKey) => CacheValue | undefined;
  delete: (key: CacheKey) => void;
  set: (key: CacheKey, value: CacheValue) => void;
  clear: () => void;
}

interface LimitedCacheArguments {
  maxSize?: number;
  log?: (...args: unknown[]) => void;
}

export function createLimitedCache<CacheValue, CacheKey = string>({
  maxSize = 100,
  log = () => null,
}: LimitedCacheArguments = {}): LimitedCache<CacheKey, CacheValue> {
  const cacheMap = new Map<CacheKey, CacheValue>();
  const cacheKeys = new Set<CacheKey>();

  function touchKey(key: CacheKey) {
    if (cacheKeys.has(key)) {
      cacheKeys.delete(key);
    }
    cacheKeys.add(key);
  }

  return {
    has: (key) => cacheMap.has(key),
    get: (key) => {
      if (cacheMap.has(key)) {
        touchKey(key);
      }
      return cacheMap.get(key);
    },
    delete: (key) => cacheMap.delete(key) && cacheKeys.delete(key),
    set: (key, value) => {
      cacheMap.set(key, value);
      touchKey(key);

      const lastKey = cacheKeys.values().toArray().shift();
      if (cacheMap.size > maxSize && lastKey) {
        cacheMap.delete(lastKey);
        cacheKeys.delete(lastKey);
        log(
          'Added %s and deleted %s from cache, now size %d',
          key,
          lastKey,
          cacheMap.size,
        );
      } else {
        log('Added %s to cache, now size %d', key, cacheMap.size);
      }
    },
    clear: () => {
      cacheMap.clear();
      cacheKeys.clear();
    },
  };
}