//當前月第一天
func firstDateOfCurrentMonth() ->NSDate{
  let calendar = NSCalendar(identifier:NSCalendarIdentifierGregorian )
  let currentDateComponents = calendar!.components([.Year,.Month], fromDate: self)
  let startOfMonth = calendar!.dateFromComponents(currentDateComponents)
  let date = startOfMonth?.dateByAddingTimeInterval(8*60*60)
  return date!
}

//當前月的第一天是星期幾
func firstDayOfCurrentMonth() -> Int {
  let calendar = NSCalendar.currentCalendar()
  let components = calendar.components(.Weekday, fromDate: firstDateOfCurrentMonth())
  return components.weekday-1
}

NSString * const kCATransitionFade;
NSString * const kCATransitionMoveIn;
NSString * const kCATransitionPush;
NSString * const kCATransitionReveal;

//為dayView（代表日歷的collectionview）添加一個滑動手勢
func addPanGestureToDayView() {
  let swipe = UIPanGestureRecognizer(target: self, action: #selector(self.panOnDayView(_:)))
  dayView.addGestureRecognizer(swipe)
}

//當在dayView上滑動時觸發(fā)
func panOnDayView(pan: UIPanGestureRecognizer) {
  //如果手勢的狀態(tài)是結(jié)束狀態(tài)
  //或者當前動畫已經(jīng)結(jié)束（防止上一個翻頁動畫還沒結(jié)束，就開始下一個）
  //添加翻頁的轉(zhuǎn)場動畫到dayView上
  if pan.state == .Ended && !animatiing{
    addAnimationToDayView(pan)
  }
}

let pageCurlDuration = 0.5  //動畫時間
let kPageCurlKey = "pageCurl"   //往上翻頁的的type
let kPageUnCurlKey = "pageUnCurl"  //往下翻頁的type

//添加動畫到日歷
func addAnimationToDayView(pan: UIPanGestureRecognizer) {
  let translation = pan.translationInView(dayView)
  //創(chuàng)建一個轉(zhuǎn)場動畫
  let transitioin = CATransition()
  transitioin.duration = pageCurlDuration
  transitioin.timingFunction = CAMediaTimingFunction(name: "default")
  //在動畫結(jié)束之后保證狀態(tài)不被移除(這個兩個屬性得同時設(shè)置)
  transitioin.fillMode = kCAFillModeForwards
  transitioin.removedOnCompletion = false
  //設(shè)置代理，在動畫開始和結(jié)束的代理方法中可以處理一些事情
  transitioin.delegate = self
  if translation.y < 0 {//手勢向上
  *
  *
    if translation.x > 0 {//手勢朝右上角滑動,朝右上翻頁
      //沿y軸對containerView進行M_PI角度翻轉(zhuǎn)，使containerView的右下角變?yōu)樽笙陆?
      animationContainerView.layer.transform = CATransform3DMakeRotation(CGFloat(M_PI), 0, 1, 0)
      //因為dayView是加在containerView上面的，如果不把dayView重新翻轉(zhuǎn)回去，顯示出來的界面都是反的
      dayView.layer.transform = CATransform3DMakeRotation(CGFloat(-M_PI), 0, 1, 0)
    }
    //轉(zhuǎn)場動畫的效果
    transitioin.type = kPageCurlKey
    //轉(zhuǎn)場動畫方向
    transitioin.subtype = kCATransitionFromBottom
    //設(shè)置一個month的key，為了在動畫結(jié)束時判斷動畫代表的是上一個月，還是下一個月
    transitioin.setValue("next", forKey: "month")
  }else{//下
    if translation.x < 0 {//手勢朝左下角滑動,朝左下翻頁
      animationContainerView.layer.transform = CATransform3DMakeRotation(CGFloat(M_PI), 0, 1, 0)
      dayView.layer.transform = CATransform3DMakeRotation(CGFloat(-M_PI), 0, 1, 0)
    }
    transitioin.type = kPageUnCurlKey
    transitioin.subtype = kCATransitionFromTop
    transitioin.setValue("pre", forKey: "month")
  }
  dayView.layer.addAnimation(transitioin, forKey: "pageCurl")
}

//因為上面設(shè)置了 transitioin.delegate = self,這兩個代理方法會自動調(diào)用
override func animationDidStart(anim: CAAnimation) {
  //動畫開始時，判斷當前動畫是代表往上翻頁，還是往下翻頁，來刷新日歷時間
  animatiing = true
  let components = GregorianCalendar?.components([.Year,.Month,.Day], fromDate: date)
  if anim.valueForKey("month") as! String == "next" {
    components?.month += 1
  }else if anim.valueForKey("month") as! String == "pre"{
    components?.month -= 1
  }
  date = (GregorianCalendar?.dateFromComponents(components!))!
  dateDidChaged!(date: date)
}

//動畫結(jié)束時，將layer的transform屬性設(shè)置為初始值,并移除dayView的layer上翻頁的動畫
override func animationDidStop(anim: CAAnimation, finished flag: Bool) {
  if flag {
    animatiing = false
    animationContainerView.layer.transform = CATransform3DIdentity
    dayView.layer.transform = CATransform3DIdentity
    dayView.layer.removeAnimationForKey("pageCurl")
  }
}