Coordinators & StateMachine - Concept

Coordinator.swift

struct Coordinator {
  let window: UIWindow
  let navCtrl: UINavigationController?
  
  func start() {
    presentWelcomeScreen()
  }
  
  private func presentWelcomeScreen() {
    let vc = WelcomeScreenViewController() // Instanciate from code, XIB, Storyboard, whatever your jam is
    vc.navTransitions = WelcomeScreenTransitions(
      showHome: self.pushHomeScreen, // see private func below
      showCreateAccountScreen: self.pushCreateAccountScreen
    )
    window.rootViewController = vc // or whatever
  }
  
  private func pushHomeScreen(user: User?) {
    let vc = HomeScreenViewController() // Instanciate from code, XIB, Storyboard, whatever your jam is
    vc.user = user // or inject a ViewModel here if you're doing MVVM, you get the idea
    
    vc.navTransitions = HomeScreenTransitions(
      showUserInfoScreen: {
        // From Home, we *push* the UserInfoVC
        self.navigationController.pushViewController(instanciateUserInfoScreen(user), animated: true, completion: nil)
      }
      showProductDetail: self.pushProductDetail // extracted in private function below
      disconnectAndShowLoginScreen: self.presentLoginScreen // same
    )
    
    navCtrl = UINavigationController(rootViewController: vc)
    window.rootViewController = navCtrl
  }
  
  private func pushProductDetail(product: Product) {
    let vc = ProductDetailViewController() // Instanciate from code, XIB, Storyboard, whatever your jam is
    vc.product = product // inject any object to the VC, like a ViewModel or whatever
    
    vc.navTransitions = ProductDetailTransitions(
      showUserInfoScreen: {
        // But from ProductDetail VC, we *present* the UserInfoVC *modally*
        self.presentViewController(instanciateUserInfoScreen(product.owner), animated: true, completion: nil)
      }
      back: { navCtrl?.popViewController(animated: true) }
    )
    
    navCtrl?.pushViewController(vc, animated: true) { _ in }
  }
  
  private func pushCreateAccountScreen() {
    // Create and push a CreateAccountViewController and its CreateAccountTransitions struct
    ...
  }
  
  private func instanciateUserInfoScreen(user: User) -> UIViewController {
    // Create, configure and return an UserDetailsViewController
    ...
  }
}

HomeScreenViewController.swift

struct HomeScreenTransitions {
  let showUserInfoScreen: Void -> Void
  let showProductDetail: Product -> Void
  let disconnectAndShowLoginScreen: Void -> Void
}

class HomeScreenViewController: UIViewController {
  var navTransitions: HomeScreenTransitions!
  
  @IBAction func profileAction(_: AnyObject) {
    navTransitions.showUserInfoScreen()
  }
  
  @IBAction func disconnectAction(_: AnyObject) {
    confirm("Are you sure?") {
      navTransitions.disconnectAndShowLoginScreen()
    }
  }
  
  @objc func tableView(tableView: UITableView, didSelectRowAtIndexPath: NSIndexPath) {
    let product = productsDataSource[indexPath.row]
    navTransitions.showProductDetail(product)
  }
}

ProductDetailViewController.swift

struct Product {
  let id: Int
  let owner: User
  ...
}

struct ProductDetailTransitions {
  let showUserInfoScreen: Void -> Void
  let back: Void -> Void
}

class ProductDetailViewController: UIViewController {
  var navTransitions: ProductDetailTransitions!
  
  @IBAction func showProductOwner(_: AnyObject) {
    navTransitions.showUserInfoScreen()
  }
  
  ...
}

WelcomeScreenViewController.swift

struct WelcomeScreenTransitions {
  let showHome: User? -> Void
  let showCreateAccountScreen: Void -> Void
}

class WelcomeScreenViewController: UIViewController {
  var navTransitions: WelcomeScreenTransitions!
  var webService: WebServiceAPI!
  
  @IBAction func loginAction(_: AnyObject) {
    webService.login(userTextField.text, passwordTextField.text) { (user: User?) in
      navTransitions.showHome(user)
    }
  }
  
  @IBAction func createAccountAction(_: AnyObject) {
    navTransitions.showCreateAccountScreen()
  }
}