ReactiveDelegates.swift

/// Shows a list of languages.
class LanguageListViewController: UIViewController {
    private let _cancel = PublishSubject<Void>()
    var didCancel: Observable<Void> { return _cancel.asObservable() }

    private let _selectLanguage = PublishSubject<String>()
    var didSelectLanguage: Observable<String> { return _selectLanguage.asObservable() }
    
    private func setupBindings() {
        cancelButton.rx.tap
            .bind(to: _cancel)
            .disposed(by: disposeBag)

        tableView.rx.itemSelected
            .map { [unowned self] in self.languages[$0.row] }
            .bind(to: _selectLanguage)
            .disposed(by: disposeBag)
    }
}

/// Shows a list of the most starred repositories filtered by a language.
class RepositoryListViewController: UIViewController {
  
  /// Subscribes on the `LanguageListViewController` observables before navigation.
  ///
  /// - Parameter viewController: `LanguageListViewController` to prepare.
  private func prepareLanguageListViewController(_ viewController: LanguageListViewController) {
          // We need to dismiss the LanguageListViewController if a language was selected or if a cancel button was tapped.
          let dismiss = Observable.merge([
              viewController.didCancel,
              viewController.didSelectLanguage.map { _ in }
              ])

          dismiss
              .subscribe(onNext: { [weak self] in self?.dismiss(animated: true) })
              .disposed(by: viewController.disposeBag)

          viewController.didSelectLanguage
              .subscribe(onNext: { [weak self] in
                  self?.currentLanguage = $0
                  self?.reloadData()
              })
              .disposed(by: viewController.disposeBag)
      }
  }
}