ScaledModalAnimationController.swift

import UIKit

class ScaledModalAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
    
    let presenting: Bool
    
    init(presenting: Bool) {
        self.presenting = presenting
    }
    
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.35
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        
        if self.presenting {
            present(using: transitionContext)
        } else {
            dismiss(using: transitionContext)
        }
    }
    
    func present(using transitionContext: UIViewControllerContextTransitioning) {
        
        guard let fromVC = transitionContext.viewController(forKey: .from), let toVC = transitionContext.viewController(forKey: .to
            ) else {
                return
        }
        let containerView = transitionContext.containerView
        
        let dimmingView = UIView(frame: fromVC.view.frame)
        dimmingView.backgroundColor = UIColor.black
        dimmingView.alpha = 0
        
        let finalFrame = transitionContext.finalFrame(for: toVC)
        toVC.view.frame = CGRect(x: 0, y: finalFrame.height, width: finalFrame.width, height: finalFrame.height)
        
        containerView.addSubview(dimmingView)
        containerView.addSubview(toVC.view)

        UIView.animate(withDuration: transitionDuration(using: transitionContext),
                       delay: 0,
                       options: [.curveEaseInOut],
                       animations: {
                        fromVC.view.transform = CGAffineTransform(scaleX: 0.95, y: 0.95)
                        dimmingView.alpha = 0.8
                        toVC.view.frame = finalFrame
        },
                       completion: { finished in
            dimmingView.removeFromSuperview()
            fromVC.view.transform = CGAffineTransform(scaleX: 1.0, y: 1.0)
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        })
    }
    
    func dismiss(using transitionContext: UIViewControllerContextTransitioning) {
        guard let fromVC = transitionContext.viewController(forKey: .from), let toVC = transitionContext.viewController(forKey: .to
            ) else {
                return
        }
        
        let containerView = transitionContext.containerView
        let finalFrame = transitionContext.finalFrame(for: toVC)
        
        toVC.view.transform = CGAffineTransform(scaleX: 0.95, y: 0.95)
    
        let dimmingView = UIView(frame: fromVC.view.frame)
        dimmingView.backgroundColor = UIColor.black
        dimmingView.alpha = 0.8
        
        containerView.addSubview(toVC.view)
        containerView.addSubview(dimmingView)
        containerView.addSubview(fromVC.view)
        
        UIView.animate(withDuration: transitionDuration(using: transitionContext),
                       delay: 0,
                       options: [.curveEaseInOut],
                       animations: {
                        toVC.view.transform = CGAffineTransform(scaleX: 1.0, y: 1.0)
                        dimmingView.alpha = 0.0
                        fromVC.view.frame = CGRect(x: 0, y: finalFrame.height, width: finalFrame.width, height: finalFrame.height)
        },
                       completion: { finished in
            dimmingView.removeFromSuperview()
            fromVC.view.removeFromSuperview()
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        })
    }
}