import RxSwift
import RxRelay
import RxDataSources

class TodoListViewModel {
    private let todoListCellViewModelsBehaviorRelay = BehaviorRelay<[TodoListCellViewModel]>(value: [])
    private var notStartedSectionObservable: Observable<TodoListSection> {
        return todoListCellViewModelsBehaviorRelay
            .flatMapLatest { viewModels -> PrimitiveSequence<SingleTrait, [TodoListCellViewModel]> in
                Observable.from(viewModels)
                    .flatMapLatest { viewModel in
                        viewModel.todoStatusObservable
                            .take(1)
                            .filter { $0 == .notStarted }
                            .map { _ in viewModel }
                    }
                    .toArray()
            }
            .map { TodoListSection(header: "Not Started", items: $0) }
    }
    private var startedSectionObserverable: Observable<TodoListSection> {
        return todoListCellViewModelsBehaviorRelay
            .flatMapLatest { viewModels -> PrimitiveSequence<SingleTrait, [TodoListCellViewModel]> in
                Observable.from(viewModels)
                    .flatMapLatest { viewModel in
                        viewModel.todoStatusObservable
                            .take(1)
                            .filter { $0 == .started }
                            .map { _ in viewModel }
                    }
                    .toArray()
            }
            .map { TodoListSection(header: "Started", items: $0) }
    }
    private var finishedSectionObservable: Observable<TodoListSection> {
        return todoListCellViewModelsBehaviorRelay
            .flatMapLatest { viewModels -> PrimitiveSequence<SingleTrait, [TodoListCellViewModel]> in
                Observable.from(viewModels)
                    .flatMapLatest { viewModel in
                        viewModel.todoStatusObservable
                            .take(1)
                            .filter { $0 == .finished }
                            .map { _ in viewModel }
                    }
                    .toArray()
            }
            .map { TodoListSection(header: "Not Started", items: $0) }
    }

    var addButtonObserver: AnyObserver<Void> {
        return AnyObserver { _ in
            let todoListCellViewModel = TodoListCellViewModel(with: Todo(title: "Todo: \(self.todoListCellViewModelsBehaviorRelay.value.count)", todoStatus: .notStarted))
            self.todoListCellViewModelsBehaviorRelay.accept(self.todoListCellViewModelsBehaviorRelay.value + [todoListCellViewModel])
        }
    }

    // 1
    var todoSelectedObserver: AnyObserver<TodoListCellViewModel> {
        return AnyObserver {
            guard
                let element = $0.element,
                let selectedViewModel = self.todoListCellViewModelsBehaviorRelay.value.first(where: { viewModel -> Bool in
                    viewModel === element
                })
                else { return }

            selectedViewModel.updateTodoStatusObserver.onNext(())
            self.todoListCellViewModelsBehaviorRelay.accept(self.todoListCellViewModelsBehaviorRelay.value)
        }
    }

    var todoListSectionsObservable: Observable<[TodoListSection]> {
        return Observable
            .combineLatest(notStartedSectionObservable, startedSectionObserverable, finishedSectionObservable)
            .map { [$0, $1, $2] }
    }

    let dataSource = RxTableViewSectionedReloadDataSource<TodoListSection>(configureCell: {dataSource, tableView, indexPath, item in
        guard let cell = tableView.dequeueReusableCell(withIdentifier: "TodoListTableViewCell") as? TodoListTableViewCell else { return UITableViewCell() }
        cell.bind(to: item)

        return cell
    })

    init() {
        dataSource.titleForHeaderInSection = { dataSource, index in
            return dataSource.sectionModels[index].header
        }
    }
}