block11.ts

// Wrap the epic to:
// - `takeUntil` the counter is removed
// - pass the local state into the counter epic
const wrappedCounterEpic = (
  counterId: string
): Epic<Action, Action, State> => (action$, state$) => {
  const counterRemovedAction$ = action$.filter(
    checkIsCounterRemovedAction
  );
  const counterStateAction$ = counterEpic(
    action$,
    // Note: this should be converted to a `StateObservable`
    // type but we've skipped this to keep the example simple.
    getCounterState(counterId)(state$.value),
    {}
  );
  const counterRemoved$ = counterRemovedAction$.filter(
    counterRemovedAction =>
      counterRemovedAction.id === counterId
  );
  return counterStateAction$.takeUntil(counterRemoved$);
};

// When an "added" action is received, start a new instance of
// the list item epic.
const rootEpic: Epic<Action, Action, State> = (
  action$,
  state$
) => {
  const counterAddedAction$ = action$.filter(
    checkIsCounterAddedAction
  );
  const counterStateAction$ = counterAddedAction$.mergeMap(
    counterAddedAction =>
      wrappedCounterEpic(counterAddedAction.id)(
        action$,
        state$,
        {}
      )
  );
  return counterStateAction$;
};