TabBarGist.swift

class TabBarController: UITabBarController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
      /// 1 - Set view Controllers using `TabBarViewModel`
      /// 2 - This iteration will create a master veiw controller embedded in a navigation controller for each tab.
      /// 3 - `inSplitViewControllerIfSupported` is a `UINavigationController` extension method that will embed it in a `UISplitViewController` if supported. 
      /// we will see the implementation later.
        viewControllers = TabBarViewModel.allCases.map { NavigationController(rootViewController: $0.masterViewController).inSplitViewControllerIfSupported(for: $0) }
    }
}

/// The view model.
enum TabBarViewModel: String, CaseIterable {
    
    case home
    case search
    case camera
    case notifications
    case profile
    /// the tab bar icon
    var icon: UIImage? {
        switch self {
        case .home: return UIImage(systemName: "house.fill")
        case .search: return UIImage(systemName: "magnifyingglass")
        case .camera: return UIImage(systemName: "plus.app")
        case .notifications: return UIImage(systemName: "suit.heart")
        case .profile: return UIImage(systemName: "person")
        }
    }
    /// the tab bar title
    var title: String {
        rawValue
    }
    /// the master `topViewController` it instantiates a view controller using a convenient method for `UIStoryboards`.
    var masterViewController: UIViewController  {
        switch self {
        case .home: return HomeViewController.instantiate(from: "Main")
        case .search: return SearchViewController.instantiate(from: "Main")
        case .camera: return HomeViewController.instantiate(from: "Main")
        case .notifications: return NotificationsViewController.instantiate(from: "Main")
        case .profile: return UserProfileViewController.instantiate(from: "Main")
        }
    }
    /// 4 - It defines if a tab should use a `UISplitViewController` as root or not.
    var inSplitViewController: Bool {
        switch self {
        case .profile:
            return true
        default:
            return false
        }
    }
}

extension UINavigationController {
  
    /// 5 - This extension returns a `SplitViewController` instance with the master and an `EmptyDetailViewcontroller` instance
  /// as a detail, if supported else will return self.
    func inSplitViewControllerIfSupported(for viewModel: TabBarViewModel) -> UIViewController {
        guard viewModel.inSplitViewController else {
            self.tabBarItem.image = viewModel.icon
            return self }
        let splitViewController = SplitViewController(viewControllers: [self, EmptyDetailViewcontroller()])
        splitViewController.tabBarItem.image = viewModel.icon
        return splitViewController
    }
}