// 這個類相當于A
class CrossDissolveFirstViewController: UIViewController, UIViewControllerTransitioningDelegate {
  // 這個對象相當于B
  crossDissolveSecondViewController.transitioningDelegate = self 

  // 點擊按鈕觸發(fā)的函數(shù)
  func animationButtonDidClicked() {
    self.presentViewController(crossDissolveSecondViewController, 
             animated: true, completion: nil)
  }

  // 下面這兩個函數(shù)定義在UIViewControllerTransitioningDelegate協(xié)議中
  // 用于為present和dismiss提供animator
  func animationControllerForPresentedController(presented: UIViewController, presentingController presenting: UIViewController, sourceController source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
//    也可以使用CrossDissolveAnimator，動畫效果各有不同
//    return CrossDissolveAnimator()
    return HalfWaySpringAnimator()
  }

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

class HalfWaySpringAnimator: NSObject, UIViewControllerAnimatedTransitioning {
  /// 設置動畫的持續(xù)時間
  func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
    return 2
  }

  /// 設置動畫的進行方式，附有詳細注釋，demo中其他地方的這個方法不再解釋
  func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
    let fromViewController = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)
    let toViewController = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey)
    let containerView = transitionContext.containerView()

    // 需要關注一下from/to和presented/presenting的關系
    // 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，盡可能使用這個方法而不是直接訪問controller的view屬性
    // 比如在form sheet樣式中，我們?yōu)閜resentedViewController的view添加陰影或其他decoration，animator會對整個decoration view
    // 添加動畫效果，而此時presentedViewController的view只是decoration view的一個子視圖
    if transitionContext.respondsToSelector(Selector("viewForKey:")) {
      fromView = transitionContext.viewForKey(UITransitionContextFromViewKey)
      toView = transitionContext.viewForKey(UITransitionContextToViewKey)
    }

    // 我們讓toview的origin.y在屏幕的一半處，這樣它從屏幕的中間位置彈起而不是從屏幕底部彈起，彈起過程中逐漸變?yōu)椴煌该?
    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時，必須將toview添加到視圖層次中
    containerView?.addSubview(toView!)

    let transitionDuration = self.transitionDuration(transitionContext)
    // 使用spring動畫，有彈簧效果，動畫結束后一定要調用completeTransition方法
    UIView.animateWithDuration(transitionDuration, delay: 0, usingSpringWithDamping: 0.6, initialSpringVelocity: 0, options: .CurveLinear, animations: { () -> Void in
      toView!.alpha = 1.0   // 逐漸變?yōu)椴煌该?
      toView?.frame = transitionContext.finalFrameForViewController(toViewController!)  // 移動到指定位置
      }) { (finished: Bool) -> Void in
        let wasCancelled = transitionContext.transitionWasCancelled()
        transitionContext.completeTransition(!wasCancelled)
    }
  }
}

// 這個相當于fromViewController
class InteractivityFirstViewController: UIViewController {
   // 這個相當于toViewController
  lazy var interactivitySecondViewController: InteractivitySecondViewController = InteractivitySecondViewController()
  // 定義了一個InteractivityTransitionDelegate類作為代理
  lazy var customTransitionDelegate: InteractivityTransitionDelegate = InteractivityTransitionDelegate()

  override func viewDidLoad() {
    super.viewDidLoad()
    setupView() // 主要是一些UI控件的布局，可以無視其實現(xiàn)細節(jié)

    /// 設置動畫代理，這個代理比較復雜，所以我們新建了一個代理對象而不是讓self作為代理
    interactivitySecondViewController.transitioningDelegate = customTransitionDelegate
  }

  // 觸發(fā)手勢時，也會調用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)
  }

  /// 前兩個函數(shù)和淡入淡出demo中的實現(xiàn)一致
  /// 后兩個函數(shù)用于實現(xiàn)交互式動畫

  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 {
  /// 當手勢有滑動時觸發(fā)這個函數(shù)
  func gestureRecognizeDidUpdate(gestureRecognizer: UIScreenEdgePanGestureRecognizer) {
    switch gestureRecognizer.state {
    case .Began: break
    case .Changed: self.updateInteractiveTransition(self.percentForGesture(gestureRecognizer)) //手勢滑動，更新百分比
    case .Ended:  // 滑動結束，判斷是否超過一半，如果是則完成剩下的動畫，否則取消動畫
      if self.percentForGesture(gestureRecognizer) >= 0.5 {
        self.finishInteractiveTransition()
      }
      else {
        self.cancelInteractiveTransition()
      }
    default: self.cancelInteractiveTransition()
    }
  }
  private func percentForGesture(gesture: UIScreenEdgePanGestureRecognizer) -> CGFloat {
    let percent = 根據gesture計算得出
    return percent
  }
}

// 這個相當于fromViewController
class CustomPresentationFirstViewController: UIViewController {
  // 這個相當于toViewController
  lazy var customPresentationSecondViewController: CustomPresentationSecondViewController = CustomPresentationSecondViewController()
  // 創(chuàng)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，可以無視其實現(xiàn)細節(jié)

    // 設置轉場動畫代理
    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? // 這個視圖封裝了原視圖，添加了陰影和圓角效果
  var dimmingView: UIView? = nil // alpha為0.5的黑色蒙版

  // 告訴UIKit為哪個視圖添加動畫效果
  override func presentedView() -> UIView? {
    return self.presentationWrappingView
  }
}

// 四個方法自定義轉場動畫發(fā)生前后的操作
extension CustomPresentationController {
  override func presentationTransitionWillBegin() {
    // 設置presentationWrappingView和dimmingView的UI效果
    let transitionCoordinator = self.presentingViewController.transitionCoordinator()
    self.dimmingView?.alpha = 0
    // 通過轉場協(xié)調器執(zhí)行同步的動畫效果
    transitionCoordinator?.animateAlongsideTransition({ (context: UIViewControllerTransitionCoordinatorContext) -> Void in
      self.dimmingView?.alpha = 0.5
      }, completion: nil)
  }

  /// present結束時，把dimmingView和wrappingView都清空，這些臨時視圖用不到了
  override func presentationTransitionDidEnd(completed: Bool) {
    if !completed {
      self.presentationWrappingView = nil
      self.dimmingView = nil
    }
  }

  /// dismiss開始時，讓dimmingView完全透明，這個動畫和animator中的動畫同時發(fā)生
  override func dismissalTransitionWillBegin() {
    let transitionCoordinator = self.presentingViewController.transitionCoordinator()
    transitionCoordinator?.animateAlongsideTransition({ (context: UIViewControllerTransitionCoordinatorContext) -> Void in
      self.dimmingView?.alpha = 0
      }, completion: nil)
  }

  /// dismiss結束時，把dimmingView和wrappingView都清空，這些臨時視圖用不到了
  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，可以無視其實現(xiàn)細節(jié)

    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;
  }