import UIKit

class CircularTransition: NSObject {

    var circle = UIView()

    var startingPoint = CGPoint.zero {
        didSet {
            circle.center = startingPoint
        }
    }

    var circleColor = UIColor.white

    var duration = 0.2

    enum CircularTransitionMode:Int {
        case present, dismiss, pop
    }

    var transitionMode:CircularTransitionMode = .present

}

extension CircularTransition:UIViewControllerAnimatedTransitioning {
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return duration
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        let containerView = transitionContext.containerView

        if transitionMode == .present {
            if let presentedView = transitionContext.view(forKey: UITransitionContextViewKey.to) {
                let viewCenter = presentedView.center
                let viewSize = presentedView.frame.size

                circle = UIView()

                circle.frame = frameForCircle(withViewCenter: viewCenter, size: viewSize, startPoint: startingPoint)

                circle.layer.cornerRadius = circle.frame.size.height / 2
                circle.center = startingPoint
                circle.backgroundColor = circleColor
                circle.transform = CGAffineTransform(scaleX: 0.001, y: 0.001)
                containerView.addSubview(circle)


                presentedView.center = startingPoint
                presentedView.transform = CGAffineTransform(scaleX: 0.001, y: 0.001)
                presentedView.alpha = 0
                containerView.addSubview(presentedView)

                UIView.animate(withDuration: duration, animations: {
                    self.circle.transform = CGAffineTransform.identity
                    presentedView.transform = CGAffineTransform.identity
                    presentedView.alpha = 1
                    presentedView.center = viewCenter

                }, completion: { (success:Bool) in
                    transitionContext.completeTransition(success)
                })
            }

        }else{
            let transitionModeKey = (transitionMode == .pop) ? UITransitionContextViewKey.to : UITransitionContextViewKey.from

            if let returningView = transitionContext.view(forKey: transitionModeKey) {
                let viewCenter = returningView.center
                let viewSize = returningView.frame.size


                circle.frame = frameForCircle(withViewCenter: viewCenter, size: viewSize, startPoint: startingPoint)

                circle.layer.cornerRadius = circle.frame.size.height / 2
                circle.center = startingPoint

                UIView.animate(withDuration: duration, animations: {
                    self.circle.transform = CGAffineTransform(scaleX: 0.001, y: 0.001)
                    returningView.transform = CGAffineTransform(scaleX: 0.001, y: 0.001)
                    returningView.center = self.startingPoint
                    returningView.alpha = 0

                    if self.transitionMode == .pop {
                        containerView.insertSubview(returningView, belowSubview: returningView)
                        containerView.insertSubview(self.circle, belowSubview: returningView)
                    }


                }, completion: { (success:Bool) in
                    returningView.center = viewCenter
                    returningView.removeFromSuperview()

                    self.circle.removeFromSuperview()

                    transitionContext.completeTransition(success)

                })

            }


        }

    }



    func frameForCircle (withViewCenter viewCenter:CGPoint, size viewSize:CGSize, startPoint:CGPoint) -> CGRect {
        let xLength = fmax(startPoint.x, viewSize.width - startPoint.x)
        let yLength = fmax(startPoint.y, viewSize.height - startPoint.y)

        let offestVector = sqrt(xLength * xLength + yLength * yLength) * 2
        let size = CGSize(width: offestVector, height: offestVector)

        return CGRect(origin: CGPoint.zero, size: size)

    }

}