export default class CachePromise<DataType = any> {
  expireTime: number;
  curTm: number = 0;
  promise: Promise<DataType> | undefined;
  pf: () => Promise<DataType>;

  constructor(pf: () => Promise<DataType>, expireTime?: number) {
    this.pf = pf;
    this.expireTime = expireTime || 0;
  }

  setNull = () => {
    this.promise = undefined;
  }

  get = async () => {
    const now = Date.now();
    if (this.expireTime && now - this.curTm > this.expireTime) {
      this.promise = this.pf();
      this.curTm = now;
    }
    if (!this.promise) {
      this.promise = this.pf();
      this.curTm = now;
    }

    const data = await this.promise;
    if (!data) {
      this.setNull();
    }

    return data;
  }
}