@AutoReducer
public abstract class AppStateReducer implements Reducer<AppState> {

    //action from TodoReducer
    @AutoReducer.Action(TodoActions.ADD_ITEM)
    AppState addItem(AppState state, TodoItem item) {
        List<TodoItem> items = state.todoItems;
        List<TodoItem> updated = TreePVector.from(items)
                .plus(item);
        return new AppState(updated, state.filter);
    }

    //action from TodoReducer
    @AutoReducer.Action(TodoActions.CHANGE_STATE)
    AppState changeState(AppState state, long id, boolean isChecked) {
        List<TodoItem> items = state.todoItems;
        for (int i = 0; i < items.size(); i++) {
            TodoItem todoItem = items.get(i);
            if (todoItem.id == id) {
                TodoItem changed = new TodoItem(id, todoItem.text, isChecked);
                PVector<TodoItem> updated = TreePVector.from(items)
                        .with(i, changed);
                return new AppState(updated, state.filter);
            }
        }
        return state;
    }

    //action from FilterReducer
    @AutoReducer.Action(TodoActions.SET_FILTER)
    AppState setFilter(AppState state, TodoFilter filter) {
        return new AppState(state.todoItems, filter);
    }

    public static AppStateReducer create() {
        return new AppStateReducerImpl();
    }
}