Allowing transition cancellation in TransitionController

Sources/iOS/TransitionController.swift

@@ -131,26 +131,30 @@ open class TransitionController: ViewController {
   open func transition(to viewController: UIViewController, completion: ((Bool) -> Void)? = nil) {
     prepare(viewController: viewController, in: container)
     
-    switch motionTransitionType {
-    case .auto:break
-    default:
-      switch viewController.motionTransitionType {
-      case .auto:
+    if case .auto = viewController.motionTransitionType {
       viewController.motionTransitionType = motionTransitionType
-      default:break
-      }
     }
     
     view.isUserInteractionEnabled = false
-    MotionTransition.shared.transition(from: rootViewController, to: viewController, in: container) { [weak self, viewController = viewController, completion = completion] (isFinishing) in
+    MotionTransition.shared.transition(from: rootViewController, to: viewController, in: container) { [weak self] isFinishing in
       guard let s = self else {
         return
       }
       
-      s.rootViewController = viewController
+      defer {
         s.view.isUserInteractionEnabled = true
         completion?(isFinishing)
       }
+      
+      guard isFinishing else {
+        s.removeViewController(viewController: viewController)
+        s.removeViewController(viewController: s.rootViewController)
+        s.prepare(viewController: s.rootViewController, in: s.container)
+        return
+      }
+      
+      s.rootViewController = viewController
+    }
   }
   
   open override func prepare() {