TODO-App-Feedback-Loop.swift

enum Event {
    case addTodo(Todo)
    case toggleTodo(Todo)
    case setVisibilityFilter(VisibilityFilter)
    case storeTodos()
    case todosStored(Bool)
}

struct State {
  var todos: [Todo]
  var visibilityFilter: VisibilityFilter
  var mustStoreTodos: Bool
}

func reduce(state: State, event: Event) -> State {
    switch event {
    case .addTodo(let todo):
        var newState = state
        newState.todos = state.todos + [todo]
        return newState
    case .toggleTodo(let todo):
        var newState = state
        newState.todos = state.todos.map { t in
            var newTodo = t
            if(todo.text == t.text) {
                newTodo.completed = !t.completed
            }
            return newTodo
        }
        return newState
    case .setVisibilityFilter(let filter):
        var newState = state
        newState.visibilityFilter = filter
        return newState
    }
    case .storeTodos():
        var newState = state
        newState.mustStoreTodos = true
        return newState
    }
    case .todosStored(let successfulStored):
        var newState = state
        newState.mustStoreTodos = false
        return newState
    }
}

func storeUserTodos(todos:[Todo]) -> AsyncResult<Context, Event, GenericError> {
    return storeUserTodosUseCase()
        .mapTT { Event.meetupsStored($0) }
}

let feedback = Feedback.react({storeUserTodos($0.todos) }, when: { $0.mustStoreTodos})