class CachedRun {
  constructor(period, request, postProcess, allwaysRun){
    this.period = period;
    this.request = request;
    this.postProcess = postProcess || (el=>el);
    this.allwaysRun = allwaysRun || (el=>el);
    this.lastCall = 0;
    this.self = this;
  }

  getFreshResults(){
    return Promise
      .resolve(this.request())
      .then(res => this.postProcess(res));
  }

  cacheResults(results){
    if(results) {
      this.cache = results;
      this.lastCall = +new Date();
    }
    return Promise
      .resolve(this.cache)
      .then(data => this.allwaysRun(data));
  }

  start(){
    return (new Date() - this.lastCall > this.period)?
      this.getFreshResults().then(res => this.cacheResults(res)) : this.cacheResults();
  }
}