ModalCardViewController.swift

//
//  ModalCardViewController.swift
//  DevsignNavigationTransitions
//
//  Created by Bryan Clark on 5/7/19.
//  Copyright © 2019 Bryan Clark. All rights reserved.
//

import UIKit
import Cartography

// When animating in/out of ModalCardViewController,
// we need to know what type of transition is going on,
// so we can animate properly.
// Think of this as a modal version of UINavigationController.Operation
fileprivate enum ModalTransitionType {
	case presentation, dismissal
}

class ModalCardViewController: UIViewController {
	private let cardView = UIView()
	private let dismissButton = UIButton()
	private let dismissTapView = UIView()
	fileprivate var currentModalTransitionType: ModalTransitionType? = nil

	fileprivate static let overlayBackgroundColor = UIColor.black.withAlphaComponent(0.4)

	init() {
		super.init(nibName: nil, bundle: nil)

		self.transitioningDelegate = self
		self.modalPresentationStyle = .overFullScreen
	}

	required init?(coder aDecoder: NSCoder) {
		fatalError("init(coder:) has not been implemented")
	}

    override func viewDidLoad() {
        super.viewDidLoad()

		self.view.backgroundColor = ModalCardViewController.overlayBackgroundColor

		// If you tap the gray background, the card dismisses
		let tapGesture = UITapGestureRecognizer(target: self, action: #selector(dismissButtonTapped))
		self.dismissTapView.addGestureRecognizer(tapGesture)
		self.view.addSubview(self.dismissTapView)
		constrain(self.dismissTapView) { $0.edges == $0.superview!.edges }

		// Let's add the rounded-corner white card
		self.cardView.backgroundColor = .white
		self.cardView.layer.cornerRadius = 12
		self.cardView.clipsToBounds = true
		self.view.addSubview(self.cardView)
		constrain(self.cardView) {
			$0.leading == $0.superview!.safeAreaLayoutGuide.leading + 8
			$0.trailing == $0.superview!.safeAreaLayoutGuide.trailing - 8
			$0.bottom == $0.superview!.safeAreaLayoutGuide.bottom - 8
			$0.height == 300
		}

		// ...and the dismiss button
		self.dismissButton.setTitle("Dismiss", for: .normal)
		self.dismissButton.setTitleColor(self.view.tintColor, for: .normal)
		self.dismissButton.addTarget(self, action: #selector(dismissButtonTapped), for: .touchUpInside)
		self.cardView.addSubview(self.dismissButton)
		constrain(self.dismissButton) {
			$0.leading == $0.superview!.leading
			$0.trailing == $0.superview!.trailing
			$0.bottom == $0.superview!.bottom
			$0.height == 50
		}
    }

	@objc private func dismissButtonTapped() {
		self.presentingViewController?.dismiss(animated: true, completion: nil)
	}
}

extension ModalCardViewController: UIViewControllerTransitioningDelegate {
	public func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
		let result = (presented == self) ? self : nil
		result?.currentModalTransitionType = .presentation
		return result
	}

	public func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
		let result = (dismissed == self) ? self : nil
		result?.currentModalTransitionType = .dismissal
		return result
	}
}

extension ModalCardViewController: UIViewControllerAnimatedTransitioning {
	private var transitionDuration: TimeInterval {
		guard let transitionType = self.currentModalTransitionType else { fatalError() }
		switch transitionType {
		case .presentation:
			return 0.44
		case .dismissal:
			return 0.32
		}
	}

	public func transitionDuration(
		using transitionContext: UIViewControllerContextTransitioning?
	) -> TimeInterval {
		return transitionDuration
	}

	public func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
		guard let transitionType = self.currentModalTransitionType else { fatalError() }

		// Here's the state we'd be in when the card is offscreen
		let cardOffscreenState = {
			let offscreenY = self.view.bounds.height - self.cardView.frame.minY + 20
			self.cardView.transform = CGAffineTransform.identity.translatedBy(x: 0, y: offscreenY)
			self.view.backgroundColor = .clear
		}

		// ...and here's the state of things when the card is onscreen.
		let presentedState = {
			self.cardView.transform = CGAffineTransform.identity
			self.view.backgroundColor = ModalCardViewController.overlayBackgroundColor
		}

		// We want different animation timing, based on whether we're presenting or dismissing.
		let animator: UIViewPropertyAnimator
		switch transitionType {
		case .presentation:
			animator = UIViewPropertyAnimator(duration: transitionDuration, dampingRatio: 0.82)
		case .dismissal:
			animator = UIViewPropertyAnimator(duration: transitionDuration, curve: UIView.AnimationCurve.easeIn)
		}

		switch transitionType {
		case .presentation:
			// We need to add the modal to the view hierarchy,
			// and perform the animation.
			let toView = transitionContext.view(forKey: .to)!
			UIView.performWithoutAnimation(cardOffscreenState)
			transitionContext.containerView.addSubview(toView)
			animator.addAnimations(presentedState)
		case .dismissal:
			// The modal is already in the view hierarchy,
			// so we just perform the animation.
			animator.addAnimations(cardOffscreenState)
		}

		// When the animation finishes,
		// we tell the system that the animation has completed,
		// and clear out our transition type.
		animator.addCompletion { (position) in
			assert(position == .end)
			transitionContext.completeTransition(true)
			self.currentModalTransitionType = nil
		}

		// ... and here's where we kick off the animation:
		animator.startAnimation()
	}
}