import { Injectable } from '@angular/core';
import { of, Observable, merge, BehaviorSubject } from 'rxjs';
import { switchMap, filter, tap, take, first, delay } from 'rxjs/operators';



@Injectable({
	providedIn: 'root'
})
export class PollingService {

	callBackEnd() {

		const getRandomResponse = () => !!Math.round(Math.random() - 0.3) ? '200' : '204';

		return of(getRandomResponse()).pipe(delay(200));
	}

	getPollingResponse() {

        /**
         * How many calls must be done
         */
		const callLimit = 5;

		/**
         * The initial value is '204' so that we can start both streams
         */
		const someSubjectTrigger$ = new BehaviorSubject('204');

		/**
 		* This stream will emit when the `callLimit` is reached, and make new server call
 		* upon response with status `204`
 		*/
		const failureStream$ = someSubjectTrigger$
			.pipe(
				take(callLimit),
				filter(x => x === '204'),
				switchMap(() => this.callBackEnd()
					.pipe(
						tap(x => someSubjectTrigger$.next(x))
					)
				),
			);

        /**
		* This stream will emit on success
		*/
		const success$ = someSubjectTrigger$.pipe(
			filter(x => x !== '204')
		);


        /**
         * Finished stream will emit once on success or on error
         */
		return merge(failureStream$, success$)
			.pipe(
				first()
			);
	}
}