store.service.ts

import { Injectable } from '@angular/core';
import { Action } from 'src/app/core/services/store/reducers';
import { BehaviorSubject, Subject } from 'rxjs';
import { scan } from 'rxjs/operators';

class Dispatcher<T> extends Subject<T> {
  dispatch(value: any): void {
    this.next(value);
  }
}

@Injectable({
  providedIn: 'root'
})
export class StoreService<T> extends BehaviorSubject<T> {

  private dispatcher = new Dispatcher();

  constructor(private reducer,
              initialState) {
    super(initialState);

    // create an temp store in memory inside of observable
    this.dispatcher.pipe(
      scan((state, action) => this.reducer(state, action), initialState))
      .subscribe(state => super.next(state));
  }

  dispatch(value: Action) {
    this.dispatcher.dispatch(value);
  }

  next(value) {
    this.dispatcher.dispatch(value);
  }
}