// repository
func addTask(task: TasksData) -> Observable<[TasksData]> {
  return Observable<[TasksData]>.create { observer -> Disposable in
    self.tasks.append(task)
    self.tasksSubject.onNext(self.tasks)
    observer.onNext(self.tasks)

    try! self.realm.write {
      self.realm.add(task)
    }

    return Disposables.create()
  }
}

// view model
func transform(input: Input) -> Output {
  let tasks = PublishSubject<[TasksData]>.init()
  let validationError = PublishSubject<String>.init()

  input.addTask
    .withUnretained(self)
    .flatMap{ (vm, data) -> Observable<[TasksData]> in
      if data.task == "" {
        validationError.onNext("할일을 입력해주세요!")
        return Observable.empty()
      } else if data.priority?.rawValue == TasksPriority.none.rawValue {
        validationError.onNext("중요도를 선택해주세요!")
        return Observable.empty()
      }
      return vm.tasksRepository.addTask(task: data)
    }
    .subscribe(onNext: { data in
      print(data)
      tasks.onNext(data)
    })
    .disposed(by: self.disposeBag)


  return Output(tasks : tasks,
                validationError: validationError)
}

// view
output.tasks
    .withUnretained(self)
    .subscribe(onNext: { (vc, data) in
        vc.dismiss(animated: false)
    })
    .disposed(by: disposeBag)

output.validationError
    .withUnretained(self)
    .subscribe(onNext: { (vc, msg) in
        vc.view.makeToast(msg)
    })
    .disposed(by: disposeBag)