Implemented the PushNavigationRouter and the ModalNavigationRouter routers for iOS platforms, with its respective BaseNavigationRouter base class.

Sources/Coordinator/Platform/iOS/Routers/BaseNavigationRouter.swift

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+//
+//  BaseNavigationRouter.swift
+//  Coordinator
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import UIKit
+
+/// This is a base class for the `NavigationRouter` concrete router implementations.
+public class BaseNavigationRouter: NSObject {
+    
+    // MARK: Properties
+    
+    /// A navigation controller to use within this concrete router.
+    var navigationController: UINavigationController
+    
+    /// Dictionary that persist `onDismiss` closure for its respective view controllers until one of the later is dismissed.
+    var onDismissForViewController: [UIViewController: Router.OnDismissedClosure] = [:]
+    
+    // MARK: Initialisers
+    
+    /// Initialise this router.
+    /// - Parameter navigationController: A `UINavigationController` navigation controller instance to use in this router.
+    init(navigationController: UINavigationController) {
+        self.navigationController = navigationController
+        
+        super.init()
+        
+        self.navigationController.delegate = self
+    }
+    
+    // MARK: Functions
+    
+    /// Executes the `onDismiss` closure for a given view controller.
+    /// - Parameter viewController: A `UIViewController` view controller instance for which the on dismiss closure will be executed.
+    func performOnDismissed(for viewController: UIViewController) {
+        guard let onDismiss = onDismissForViewController[viewController] else {
+            return
+        }
+        
+        onDismiss()
+        
+        onDismissForViewController[viewController] = nil
+    }
+    
+}
+
+// MARK: - UINavigationControllerDelegate
+
+extension BaseNavigationRouter: UINavigationControllerDelegate {
+    
+    // MARK: Functions
+    
+    public func navigationController(
+        _ navigationController: UINavigationController,
+        didShow viewController: UIViewController,
+        animated: Bool
+    ) {
+        guard let dismissedViewController = navigationController.transitionCoordinator?.viewController(forKey: .from) else {
+            return
+        }
+        
+        performOnDismissed(for: dismissedViewController)
+    }
+
+}

Sources/Coordinator/Platform/iOS/Routers/ModalNavigationRouter.swift

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+//
+//  ModalNavigationRouter.swift
+//  Coordinator
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import UIKit
+
+public class ModalNavigationRouter: BaseNavigationRouter {
+    
+    // MARK: Properties
+    
+    /// The parent view controller from where this router is being called from.
+    public unowned let parentViewController: UIViewController
+
+    // MARK: Initialisers
+    
+    /// Initialise this router.
+    /// - Parameter parentViewController: A `UIViewController` view controller instance from where this router is originated.
+    public init(parentViewController: UIViewController) {
+        self.parentViewController = parentViewController
+        
+        super.init(navigationController: .init())
+    }
+    
+}
+
+extension ModalNavigationRouter: Router {
+    public func present(
+        _ viewController: UIViewController,
+        animated: Bool,
+        onDismiss: OnDismissedClosure?
+    ) {
+        onDismissForViewController[viewController] = onDismiss
+        
+        if navigationController.viewControllers.isEmpty {
+            presentModally(viewController, animated: animated)
+        } else {
+            navigationController.pushViewController(viewController, animated: animated)
+        }
+    }
+    
+    public func dismiss(animated: Bool) {
+        guard let firstViewController = navigationController.viewControllers.first else {
+            return
+        }
+        
+        performOnDismissed(for: firstViewController)
+        
+        parentViewController.dismiss(animated: animated)
+    }
+    
+}
+
+// MARK: - Helpers
+
+private extension ModalNavigationRouter {
+    
+    // MARK: Functions
+    
+    func presentModally(_ viewController: UIViewController, animated: Bool) {
+        viewController.navigationItem.leftBarButtonItem = UIBarButtonItem(
+            title: "Cancel",
+            style: .plain,
+            target: self,
+            action: #selector(onCancelPressed)
+        )
+        
+        navigationController.setViewControllers([viewController], animated: false)
+        
+        parentViewController.present(navigationController, animated: animated)
+    }
+    
+    @objc func onCancelPressed() {
+        guard let firstViewController = navigationController.viewControllers.first else {
+            return
+        }
+        
+        performOnDismissed(for: firstViewController)
+        dismiss(animated: true)
+    }
+    
+}

Sources/Coordinator/Platform/iOS/Routers/PushNavigationRouter.swift

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+//
+//  PushNavigationRouter.swift
+//  Coordinator
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import UIKit
+
+/// This class is responsible for presenting view controllers, as it is a concrete implementation of the `Router` protocol, but it won't know what view controller or which view controller is next.
+public class PushNavigationRouter: BaseNavigationRouter {
+    
+    // MARK: Properties
+    
+    /// A root view controller coming in from the navigation controller, if any.
+    private let rootViewController: UIViewController?
+    
+    // MARK: Initialisers
+    
+    /// Initialise this router.
+    /// - Parameters:
+    ///   - navigationController: A `UINavigationController` navigation controller instance to use in this router.
+    ///   - rootViewController: A `UIViewController` view controller instance to define as a root view controller of the navigation controller.
+    /// - Note This initialiser added the `rootViewController` parameter although it is not really needed to differentiate itself from the `.init(navigationController:)` implemented for the `BaseNavigationRouter` base class.
+    public init(
+        navigationController: UINavigationController,
+        rootViewController: UIViewController? = nil
+    ) {
+        self.rootViewController = navigationController.viewControllers.first ?? rootViewController
+
+        super.init(navigationController: navigationController)
+    }
+
+}
+
+// MARK: - Router
+
+extension PushNavigationRouter: Router {
+    
+    // MARK: Functions
+    
+    public func present(
+        _ viewController: UIViewController,
+        animated: Bool,
+        onDismiss: OnDismissedClosure?
+    ) {
+        onDismissForViewController[viewController] = onDismiss
+        
+        navigationController.pushViewController(viewController, animated: animated)
+    }
+    
+    public func dismiss(animated: Bool) {
+        guard let rootViewController else {
+            navigationController.popViewController(animated: animated)
+            return
+        }
+        
+        performOnDismissed(for: rootViewController)
+        
+        navigationController.popToViewController(rootViewController, animated: animated)
+    }
+    
+}