import Rx from "rxjs";

class Throttler {
  /**
   * A Subject behaves as an event stream. You pump values
   * into the stream and each value gets pumped through
   * the pipeline below.
   */
  request$ = new Rx.Subject();

  constructor() {
    this.request$
      /* Scan keeps track of what request number we're on. */
      .scan((acc, url, index) => {
        const delay = (index < 5)
          ? (index === 0) ? 0 : 1
          : 1000;

        return {
          url: url,
          delay: delay
        };
      }, {})
      .flatMap(({ url, delay }) => {
        /* Timer will delay by the given `delay`
         and then make the request. */
        return Rx.Observable.timer(delay)
          .flatMap(() =>
            Rx.Observable.fromPromise(
              // axios.get(url, { responseType: 'json' })
              new Promise( ( resolve, reject ) => {
                setTimeout(function () { resolve({data: url}); }, 3000)
              } )

            )
          );
      })
      /* subscribe() receives responses as they stream through. */
      .subscribe((data) => {
        console.log(data);
      });
  }

  makeRequest(url) {
    this.request$.next(url); // Pumps the URL into the stream.
  }
}

export default Throttler;