MVVM-C Coordinator

CountryListCoordinator.swift

import Foundation
import UIKit

final class CountryListCoordinator: Coordinator {
    
    private enum LocalizedStrings {
        static let okTitle = "Ok"
        static let errorTitle = "Error"
        static let errorMessage = "Could not search country for the keyword."
    }
    
    var finished: (() -> Void)?
    
    var childCoordinators: [Coordinator]?
    
    private var childNavigationController: UINavigationController?
    private weak var viewController: CountryListViewController?
    private let requestManager: RequestManager
    
    init(requestManager: RequestManager) {
        self.requestManager = requestManager
    }
    
    func start() -> UIViewController {
        let viewController: CountryListViewController =  UIStoryboard.mainStoryBoard().instantiateViewController()
        self.viewController = viewController
        
        let countryListViewModel = CountryListViewModel(requestManager: requestManager)
        countryListViewModel.loadingErrorDelegate = self
        viewController.configure(viewModel: countryListViewModel)
        viewController.delegate = self
        
        return viewController
    }
    
}

extension CountryListCoordinator: CountryListViewControllerDelegate {
    
    func didSelect(country: Country, in viewController: UIViewController) {
        let coordinator = CountryDetailCoordinator(country: country)
        let detailViewController = coordinator.start()
        
        let childNavigationController = UINavigationController(rootViewController: detailViewController)
        self.childNavigationController = childNavigationController
        
        let doneButton = UIBarButtonItem(barButtonSystemItem: .done,
                                         target: self,
                                         action: #selector(doneButtonClicked))
        detailViewController.navigationItem.leftBarButtonItem = doneButton
        viewController.present(childNavigationController, animated: true, completion: nil)
    }
    
    @objc private func doneButtonClicked(_ sender: UIBarButtonItem) {
        childNavigationController?.dismiss(animated: true, completion: nil)
    }
    
}

extension CountryListCoordinator: CountryListViewModelLoadingErrorDelegate {
    
    func didFailLoading(error: Error) {
        guard let viewController = viewController else {
            assertionFailure("viewController of CountryListCoordinator can not be nil.\(#function)")
            return
        }
        
        let alert = UIAlertController(title: LocalizedStrings.errorTitle,
                                      message: LocalizedStrings.errorMessage,
                                      preferredStyle: .alert)
        
        let okAction = UIAlertAction(title: LocalizedStrings.okTitle,
                                     style: .default,
                                     handler: nil)
        alert.addAction(okAction)
        
        viewController.present(alert, animated: true, completion: nil)
    }
}