Rerun observable until the response meets a given condition

repeatUntil.operator.ts

export type RepeatUntilOperator = <T>(
  conditionChecker: (response: T) => boolean,
  delayInterval?: number
) => (source$: Observable<T>) => Observable<T>;

/**
 * Rerun source observable until the response meets a defined condition.
 * @param conditionChecker Function which checks every response for a given condition
 * @param delayInterval [Optional] Delay between a response and a new request if condition is not met. Unit: ms. Default: 5000.
 */
export const repeatUntil: RepeatUntilOperator = <T>(
  conditionChecker: (response: T) => boolean,
  delayInterval: number = 5000
) =>
  (source$: Observable<T>) =>
    new Observable((observer: Subscriber<T>) => {
      const load$: BehaviorSubject<null> = new BehaviorSubject<null>(null);

      const refresh$: Observable<null> = of<null>(null).pipe(
        delay(delayInterval),
        tap(() => load$.next(null)),
        skip(1)
      );

      const repeat$: Observable<T> = concat(source$, refresh$);

      load$.pipe(
        concatMap(() => repeat$),
        filter((response) => conditionChecker(response)),
        take(1)
      ).subscribe(observer);
    });

yourHttp.service.ts

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

  static BASE_URL = `${environment.apigateway}/report`;
  static STATUS_URL = `${VeryImportantHttpService.BASE_URL}/status`;
  static DOWNLOAD_URL = `${VeryImportantHttpService.BASE_URL}/download`;

  constructor(private http: HttpClient) {}
  
  getImportantReport() {
    return this.http.get<{ reportId: string; }>(YourHttpService.BASE_URL)
      .pipe(
        switchMap(({ reportId }) => 
          this.http.get<{ status: 'IN_PROGRESS'|'DONE' }>(YourHttpService.STATUS_URL, { reportId })
            .pipe(
              repeatUntil(({ status }) => status === 'DONE', 2000),
              map(() => reportId)
            )
        ),
        switchMap(({ reportId }) => 
          this.http.get<{ url: string }>(YourHttpService.DOWNLOAD_URL, { reportId })
            .pipe(
              map(({ url }) => url)
            )
        )
    )
  }

}