Custom popup presenting transition

poptransition.swift

import Foundation
import UIKit

final class PopupTransition: NSObject, UIViewControllerAnimatedTransitioning {
  
  enum Mode {
    case present
    case dismiss
  }

  let duration: TimeInterval
  let originFrame: CGRect
  let mode: Mode
  
  init(duration: TimeInterval, originFrame: CGRect, mode: Mode) {
    self.duration = duration
    self.originFrame = originFrame
    self.mode = mode
  }

  func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
    return self.duration
  }
  
  func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
    switch mode {
    case .present:
      presentAnimation(using: transitionContext)
    case .dismiss:
      dismissAnimation(using: transitionContext)
    }
  }
  
  private func presentAnimation(using transitionContext: UIViewControllerContextTransitioning) {
    // Setup
    let containerView = transitionContext.containerView
    let toView = transitionContext.view(forKey: .to)!
    let initialFrame = originFrame
    let finalFrame = toView.frame
    
    toView.transform = CGAffineTransform(
      scaleX: initialFrame.width / finalFrame.width,
      y: initialFrame.height / finalFrame.height
    )
    toView.center = CGPoint(x: initialFrame.midX, y: initialFrame.midY)
    containerView.addSubview(toView)

    UIView.animate(
      withDuration: duration,
      delay: 0.0,
      usingSpringWithDamping: 0.4,
      initialSpringVelocity: 0.0,
      animations: {
        toView.transform = .identity
        toView.center = CGPoint(x: finalFrame.midX, y: finalFrame.midY)
      },
      completion: { _ in
        transitionContext.completeTransition(true)
      }
    )
  }
  
  private func dismissAnimation(using transitionContext: UIViewControllerContextTransitioning) {
    // Setup
    let containerView = transitionContext.containerView
    let fromView = transitionContext.view(forKey: .from)!
    let toView = transitionContext.view(forKey: .to)!
    let initialFrame = fromView.frame
    let finalFrame = originFrame
    
    containerView.addSubview(toView)
    containerView.bringSubview(toFront: fromView)
    
    // Animation
    UIView.animate(
      withDuration: duration,
      delay: 0.0,
      usingSpringWithDamping: 0.4,
      initialSpringVelocity: 0.0,
      animations: {
        fromView.transform = CGAffineTransform(
          scaleX: finalFrame.width / initialFrame.width,
          y: finalFrame.height / initialFrame.height
        )
        fromView.center = CGPoint(x: finalFrame.midX, y: finalFrame.midY)
      },
      completion: { _ in
        transitionContext.completeTransition(true)
      }
    )
  }
}