import { HttpClient } from '@angular/common/http';
import { Subject, Subscription, BehaviorSubject } from 'rxjs';
import { retryWhen, delay, tap, skip } from 'rxjs/operators';

export class StatusCodePoller {
  http: HttpClient;
  url: BehaviorSubject<string>;
  pollFreq: number;
  okCode: number;
  stopOnOk: boolean;

  pollSubscription: Subscription;
  urlSubscription: Subscription;
  poll = new Subject<any>();
  ok = new Subject<any>();
  isPolling = new BehaviorSubject<boolean>(false);

  constructor(
      url: BehaviorSubject<string>, http: HttpClient,
      pollFreq = 1000, okCode = 200,
      stopOnOk = true
    ) {
    this.url = url;
    this.http = http;
    this.pollFreq = pollFreq;
    this.okCode = okCode;
    this.stopOnOk = stopOnOk;
  }

  start() {
    this.stop();
    if (this.url.value === '') {
      return;
    }
    this.urlSubscription = this.url.pipe(skip(1)).subscribe(() => this.stop());
    this.isPolling.next(true);
    this.pollSubscription = this.http.get(this.url.value, {observe: 'response'}).pipe(
      retryWhen(errors =>
        errors.pipe(
          tap(
            response => {
              this.poll.next(response);
              if (response.status === this.okCode) {
                if (this.stopOnOk) {
                  this.stop();
                }
                this.ok.next(response);
              }
          }),
          delay(this.pollFreq)
    ))).subscribe();
  }

  stop() {
    this.isPolling.next(false);
    if (this.pollSubscription) {
      this.pollSubscription.unsubscribe();
    }
    if (this.urlSubscription) {
      this.urlSubscription.unsubscribe();
    }
  }
}