// 这个类相当于A
class CrossDissolveFirstViewController: UIViewController, UIViewControllerTransitioningDelegate {
  // 这个对象相当于B
  crossDissolveSecondViewController.transitioningDelegate = self 

  // 点击按钮触发的函数
  func animationButtonDidClicked() {
    self.presentViewController(crossDissolveSecondViewController, 
             animated: true, completion: nil)
  }

  // 下面这两个函数定义在UIViewControllerTransitioningDelegate协议中
  // 用于为present和dismiss提供animator
  func animationControllerForPresentedController(presented: UIViewController, presentingController presenting: UIViewController, sourceController source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
//    也可以使用CrossDissolveAnimator，动画效果各有不同
//    return CrossDissolveAnimator()
    return HalfWaySpringAnimator()
  }

  func animationControllerForDismissedController(dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    return CrossDissolveAnimator()
  }
}

class HalfWaySpringAnimator: NSObject, UIViewControllerAnimatedTransitioning {
  /// 设置动画的持续时间
  func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
    return 2
  }

  /// 设置动画的进行方式，附有详细注释，demo中其他地方的这个方法不再解释
  func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
    let fromViewController = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)
    let toViewController = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey)
    let containerView = transitionContext.containerView()

    // 需要关注一下from/to和presented/presenting的关系
    // For a Presentation:
    //   fromView = The presenting view.
    //   toView  = The presented view.
    // For a Dismissal:
    //   fromView = The presented view.
    //   toView  = The presenting view.

    var fromView = fromViewController?.view
    var toView = toViewController?.view

    // iOS8引入了viewForKey方法，尽可能使用这个方法而不是直接访问controller的view属性
    // 比如在form sheet样式中，我们为presentedViewController的view添加阴影或其他decoration，animator会对整个decoration view
    // 添加动画效果，而此时presentedViewController的view只是decoration view的一个子视图
    if transitionContext.respondsToSelector(Selector("viewForKey:")) {
      fromView = transitionContext.viewForKey(UITransitionContextFromViewKey)
      toView = transitionContext.viewForKey(UITransitionContextToViewKey)
    }

    // 我们让toview的origin.y在屏幕的一半处，这样它从屏幕的中间位置弹起而不是从屏幕底部弹起，弹起过程中逐渐变为不透明
    toView?.frame = CGRectMake(fromView!.frame.origin.x, fromView!.frame.maxY / 2, fromView!.frame.width, fromView!.frame.height)
    toView?.alpha = 0.0

    // 在present和，dismiss时，必须将toview添加到视图层次中
    containerView?.addSubview(toView!)

    let transitionDuration = self.transitionDuration(transitionContext)
    // 使用spring动画，有弹簧效果，动画结束后一定要调用completeTransition方法
    UIView.animateWithDuration(transitionDuration, delay: 0, usingSpringWithDamping: 0.6, initialSpringVelocity: 0, options: .CurveLinear, animations: { () -> Void in
      toView!.alpha = 1.0   // 逐渐变为不透明
      toView?.frame = transitionContext.finalFrameForViewController(toViewController!)  // 移动到指定位置
      }) { (finished: Bool) -> Void in
        let wasCancelled = transitionContext.transitionWasCancelled()
        transitionContext.completeTransition(!wasCancelled)
    }
  }
}

// 这个相当于fromViewController
class InteractivityFirstViewController: UIViewController {
   // 这个相当于toViewController
  lazy var interactivitySecondViewController: InteractivitySecondViewController = InteractivitySecondViewController()
  // 定义了一个InteractivityTransitionDelegate类作为代理
  lazy var customTransitionDelegate: InteractivityTransitionDelegate = InteractivityTransitionDelegate()

  override func viewDidLoad() {
    super.viewDidLoad()
    setupView() // 主要是一些UI控件的布局，可以无视其实现细节

    /// 设置动画代理，这个代理比较复杂，所以我们新建了一个代理对象而不是让self作为代理
    interactivitySecondViewController.transitioningDelegate = customTransitionDelegate
  }

  // 触发手势时，也会调用animationButtonDidClicked方法
  func interactiveTransitionRecognizerAction(sender: UIScreenEdgePanGestureRecognizer) {
    if sender.state == .Began {
      self.animationButtonDidClicked(sender)
    }
  }

  func animationButtonDidClicked(sender: AnyObject) {
    self.presentViewController(interactivitySecondViewController, animated: true, completion: nil)
  }
}

class InteractivityTransitionDelegate: NSObject, UIViewControllerTransitioningDelegate {
  func animationControllerForPresentedController(presented: UIViewController, presentingController presenting: UIViewController, sourceController source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    return InteractivityTransitionAnimator(targetEdge: targetEdge)
  }

  func animationControllerForDismissedController(dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    return InteractivityTransitionAnimator(targetEdge: targetEdge)
  }

  /// 前两个函数和淡入淡出demo中的实现一致
  /// 后两个函数用于实现交互式动画

  func interactionControllerForPresentation(animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
    return TransitionInteractionController(gestureRecognizer: gestureRecognizer, edgeForDragging: targetEdge)
  }

  func interactionControllerForDismissal(animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
    return TransitionInteractionController(gestureRecognizer: gestureRecognizer, edgeForDragging: targetEdge)
  }
}

class TransitionInteractionController: UIPercentDrivenInteractiveTransition {
  /// 当手势有滑动时触发这个函数
  func gestureRecognizeDidUpdate(gestureRecognizer: UIScreenEdgePanGestureRecognizer) {
    switch gestureRecognizer.state {
    case .Began: break
    case .Changed: self.updateInteractiveTransition(self.percentForGesture(gestureRecognizer)) //手势滑动，更新百分比
    case .Ended:  // 滑动结束，判断是否超过一半，如果是则完成剩下的动画，否则取消动画
      if self.percentForGesture(gestureRecognizer) >= 0.5 {
        self.finishInteractiveTransition()
      }
      else {
        self.cancelInteractiveTransition()
      }
    default: self.cancelInteractiveTransition()
    }
  }
  private func percentForGesture(gesture: UIScreenEdgePanGestureRecognizer) -> CGFloat {
    let percent = 根据gesture计算得出
    return percent
  }
}

// 这个相当于fromViewController
class CustomPresentationFirstViewController: UIViewController {
  // 这个相当于toViewController
  lazy var customPresentationSecondViewController: CustomPresentationSecondViewController = CustomPresentationSecondViewController()
  // 创建PresentationController
  lazy var customPresentationController: CustomPresentationController = CustomPresentationController(presentedViewController: self.customPresentationSecondViewController, presentingViewController: self)

  override func viewDidLoad() {
    super.viewDidLoad()
    setupView() // 主要是一些UI控件的布局，可以无视其实现细节

    // 设置转场动画代理
    customPresentationSecondViewController.transitioningDelegate = customPresentationController
  }

  override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
  }

  func animationButtonDidClicked() {
    self.presentViewController(customPresentationSecondViewController, animated: true, completion: nil)
  }
}

class CustomPresentationController: UIPresentationController, UIViewControllerTransitioningDelegate {
  var presentationWrappingView: UIView? // 这个视图封装了原视图，添加了阴影和圆角效果
  var dimmingView: UIView? = nil // alpha为0.5的黑色蒙版

  // 告诉UIKit为哪个视图添加动画效果
  override func presentedView() -> UIView? {
    return self.presentationWrappingView
  }
}

// 四个方法自定义转场动画发生前后的操作
extension CustomPresentationController {
  override func presentationTransitionWillBegin() {
    // 设置presentationWrappingView和dimmingView的UI效果
    let transitionCoordinator = self.presentingViewController.transitionCoordinator()
    self.dimmingView?.alpha = 0
    // 通过转场协调器执行同步的动画效果
    transitionCoordinator?.animateAlongsideTransition({ (context: UIViewControllerTransitionCoordinatorContext) -> Void in
      self.dimmingView?.alpha = 0.5
      }, completion: nil)
  }

  /// present结束时，把dimmingView和wrappingView都清空，这些临时视图用不到了
  override func presentationTransitionDidEnd(completed: Bool) {
    if !completed {
      self.presentationWrappingView = nil
      self.dimmingView = nil
    }
  }

  /// dismiss开始时，让dimmingView完全透明，这个动画和animator中的动画同时发生
  override func dismissalTransitionWillBegin() {
    let transitionCoordinator = self.presentingViewController.transitionCoordinator()
    transitionCoordinator?.animateAlongsideTransition({ (context: UIViewControllerTransitionCoordinatorContext) -> Void in
      self.dimmingView?.alpha = 0
      }, completion: nil)
  }

  /// dismiss结束时，把dimmingView和wrappingView都清空，这些临时视图用不到了
  override func dismissalTransitionDidEnd(completed: Bool) {
    if completed {
      self.presentationWrappingView = nil
      self.dimmingView = nil
    }
  }
}

extension CustomPresentationController {
}

class FromViewController: UIViewController, UINavigationControllerDelegate {
  let toViewController: ToViewController = ToViewController()

  override func viewDidLoad() {
    super.viewDidLoad()
    setupView() // 主要是一些UI控件的布局，可以无视其实现细节

    self.navigationController.delegate = self
  }
}

func navigationController(navigationController: UINavigationController, 
   animationControllerForOperation operation: UINavigationControllerOperation, 
           fromViewController fromVC: UIViewController, 
             toViewController toVC: UIViewController) 
            -> UIViewControllerAnimatedTransitioning? {
    if operation == .Push {
      return PushAnimator()
    }
    if operation == .Pop {
      return PopAnimator()
    }
    return nil;
  }