import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';

import 'rxjs/add/operator/combineLatest';
import 'rxjs/add/operator/mapTo';
import 'rxjs/add/operator/merge';

@Injectable()
export class LoadingFailedService {

  private reloadSubject = new Subject();

  public data$: Observable<any>;
  public failed$: Observable<boolean>;
  public loading$: Observable<boolean>;

  constructor() {}

  public reload() {
    this.reloadSubject.next(true);
  }

  // setup the load-fail-service with a parameterstream and the function to be loaded/failed
  public setup(inputStream: Observable<any>, promiseFunction: (any) => Promise<any>) {
    const reload$ = this.reloadSubject.asObservable().startWith(true);
    const inputRequest$ = inputStream.combineLatest(reload$, (id, _) => id);

    const assignmentRequest$ = inputRequest$
      // todo: find a better solution for this 'mapping to null on error'
      .switchMap(params => promiseFunction(params).catch(e => null))
      .share();

    const data$ = assignmentRequest$.filter(val => val !== null);
    const failedRequest$ = assignmentRequest$.filter(val => val === null);

    const loading$ = Observable.merge(
      inputRequest$.mapTo(true),
      assignmentRequest$.mapTo(false));

    const failed$ = failedRequest$.mapTo(true)
      .merge(data$.mapTo(false))
      .combineLatest(loading$, (failed, loading) => failed && !loading);

    this.loading$ = loading$;
    this.failed$ = failed$;
    this.data$ = data$;
  }
}