WithBlockingView.swift

//
//  WithBlockingView.swift
//

extension ObservableConvertibleType {
    /// actionがcompleteするまで画面を表示する
    func withBlockingView(from parentViewController: UIViewController) -> Observable<Element> {
        let viewController = _BlockingLoadingViewController(self)
        return viewController.result
            .do(onSubscribed: { [weak parentViewController] in
                DispatchQueue.main.async {
                    parentViewController?.present(viewController, animated: true, completion: nil)
                }
            })
    }
}

/// 特定の操作のため、ブロックするための画面を出す。
/// 必ずcompleteさせること
private final class _BlockingLoadingViewController<T>: UIViewController {
    private let _indicator = UIActivityIndicatorView(style: .gray)
    private let disposeBag = DisposeBag()
    private let _action: Observable<T>
    private let _publisher = PublishSubject<T>()
    
    fileprivate var result: Observable<T> {
        return _publisher
            .takeUntil(rx.deallocated)
    }
    
    init<O: ObservableConvertibleType>(_ action: O) where O.Element == T {
        _action = action.asObservable()
        super.init(nibName: nil, bundle: nil)
        modalPresentationStyle = .overCurrentContext
        modalTransitionStyle = .crossDissolve
    }
    
    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = UIColor(displayP3Red: 1.0, green: 1.0, blue: 1.0, alpha: 0.7)
        
        _indicator.hidesWhenStopped = true
        view.addSubview(_indicator)
        _indicator.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            _indicator.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            _indicator.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ])
        _indicator.startAnimating()
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        _action
            .retryWhen({ [weak self] error -> Observable<Void> in
                return error
                    .flatMap { _ in
                        return self?._showRetryAlert() ?? .empty()
                    }
            })
            .do(onCompleted: { [weak self] in
                DispatchQueue.main.async {
                    self?.dismiss(animated: true, completion: nil)
                }
            })
            .bind(to: _publisher)
            .disposed(by: disposeBag)
    }
    
    private func _showRetryAlert() -> Observable<Void> {
        let publisher = PublishSubject<Void>()
        DispatchQueue.main.async { [weak self] in
            let alertController = UIAlertController(title: "エラー", message: "再試行しますか？", preferredStyle: .alert)
            alertController.addAction(UIAlertAction(title: "キャンセル", style: .cancel, handler: { _ in
                self?.dismiss(animated: true, completion: nil)
                publisher.onCompleted()
            }))
            alertController.addAction(UIAlertAction(title: "再試行", style: .default, handler: { _ in
                publisher.onNext(())
                publisher.onCompleted()
            }))
            self?.present(alertController, animated: true, completion: nil)
        }
        return publisher
    }
}