import { Observable, empty } from 'rxjs';
import {
  distinctUntilChanged,
  filter,
  map,
  mergeMapTo,
  tap
} from 'rxjs/operators';

import { RootState } from 'wdk-client/Core/State/Types';

// Perform a side effect based on state changes
export function stateEffect<K>(state$: Observable<RootState>, getValue: (state: RootState) => K, effect: (value: NonNullable<K>) => void) {
  return state$.pipe(
    map(getValue),
    filter((value): value is NonNullable<K> => value != null),
    distinctUntilChanged(),
    tap(effect),
    mergeMapTo(empty())
  );
}