SwipeNavigationController.swift

import UIKit

class SwipeNavigationController: UINavigationController {
    /// Make sure you set  CADisableMinimumFrameDurationOnPhone to true in Info.plist
    /// Otherwise the smoothness won't be that good as with "targets" approach:
    /// https://gist.github.com/kopyl/78600e5a9e0865dac02fdbd7d845139b

    private var isInteractiveTransition = false
    private var transitionFromVC: UIViewController?
    private var transitionToVC: UIViewController?
    private var transitionContainerView: UIView?

    private var frameRateLink: CADisplayLink?

    override func viewDidLoad() {
        super.viewDidLoad()

        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(handlePan(_:)))
        panGesture.delegate = self
        view.addGestureRecognizer(panGesture)

        interactivePopGestureRecognizer?.isEnabled = false
    }

    @objc private func handlePan(_ gesture: UIPanGestureRecognizer) {
        let translation = gesture.translation(in: view)
        let progress = max(0, min(1, translation.x / view.bounds.width))

        switch gesture.state {
        case .began:
            beginInteractiveTransition()

        case .changed:
            updateInteractiveTransition(progress: progress)

        case .ended, .cancelled:
            let velocity = gesture.velocity(in: view).x
            let shouldComplete = progress > 0.2 || velocity > 800
            endInteractiveTransition(progress: progress, velocity: velocity, shouldComplete: shouldComplete)

        default:
            cancelTransition()
        }
    }

    private func beginInteractiveTransition() {
        guard viewControllers.count > 1,
              let fromVC = viewControllers.last,
              let toVC = viewControllers.dropLast().last,
              let containerView = fromVC.view.superview else { return }

        isInteractiveTransition = true
        transitionFromVC = fromVC
        transitionToVC = toVC
        transitionContainerView = containerView

        startFrameRateKeepAlive()

        toVC.view.removeFromSuperview()
        toVC.view.frame = CGRect(x: -containerView.bounds.width * 0.3, y: 0, width: containerView.bounds.width, height: containerView.bounds.height)
        containerView.insertSubview(toVC.view, belowSubview: fromVC.view)

        fromVC.beginAppearanceTransition(false, animated: true)
        toVC.beginAppearanceTransition(true, animated: true)
    }

    private func updateInteractiveTransition(progress: CGFloat) {
        guard isInteractiveTransition,
              let fromVC = transitionFromVC,
              let toVC = transitionToVC,
              let containerView = transitionContainerView else { return }

        let width = containerView.bounds.width
        let height = containerView.bounds.height

        fromVC.view.frame = CGRect(x: progress * width, y: 0, width: width, height: height)
        toVC.view.frame = CGRect(x: (progress - 1.0) * width * 0.3, y: 0, width: width, height: height)
    }

    private func endInteractiveTransition(progress: CGFloat, velocity: CGFloat, shouldComplete: Bool) {
        guard isInteractiveTransition,
              let fromVC = transitionFromVC,
              let toVC = transitionToVC,
              let containerView = transitionContainerView else { return }

        let width = containerView.bounds.width
        let height = containerView.bounds.height

        if shouldComplete {
            let remainingDistance = (1 - progress) * width
            let duration = abs(velocity) < 1 ? 0.35 : Double(min(0.35, max(0.1, remainingDistance / abs(velocity))))

            UIView.animate(withDuration: duration, delay: 0, options: .curveEaseOut) {
                fromVC.view.frame = CGRect(x: width, y: 0, width: width, height: height)
                toVC.view.frame = containerView.bounds
            } completion: { _ in
                self.completeTransition()
            }
        } else {
            let duration = Double(min(0.35, max(0.1, progress * width / max(abs(velocity), 300))))

            UIView.animate(withDuration: duration, delay: 0, options: .curveEaseOut) {
                fromVC.view.frame = containerView.bounds
                toVC.view.frame = CGRect(x: -width * 0.3, y: 0, width: width, height: height)
            } completion: { _ in
                self.cancelTransition()
            }
        }
    }

    private func startFrameRateKeepAlive() {
        frameRateLink?.invalidate()
        let link = CADisplayLink(target: self, selector: #selector(frameRateLinkFired))
        if #available(iOS 15.0, *) {
            let maxFps = Float(UIScreen.main.maximumFramesPerSecond)
            link.preferredFrameRateRange = CAFrameRateRange(minimum: maxFps, maximum: maxFps, preferred: maxFps)
        }
        link.add(to: .main, forMode: .common)
        frameRateLink = link
    }

    private func stopFrameRateKeepAlive() {
        frameRateLink?.invalidate()
        frameRateLink = nil
    }

    @objc private func frameRateLinkFired(_ link: CADisplayLink) {}

    private func completeTransition() {
        guard let fromVC = transitionFromVC,
              let toVC = transitionToVC,
              let containerView = transitionContainerView else {
            cleanupTransition()
            return
        }
        
        fromVC.view.removeFromSuperview()
        toVC.view.frame = containerView.bounds

        fromVC.endAppearanceTransition()
        toVC.endAppearanceTransition()

        popViewController(animated: false)
        cleanupTransition()
    }

    private func cancelTransition() {
        guard let fromVC = transitionFromVC,
              let toVC = transitionToVC,
              let containerView = transitionContainerView else {
            cleanupTransition()
            return
        }
        
        fromVC.view.frame = containerView.bounds
        toVC.view.removeFromSuperview()

        fromVC.beginAppearanceTransition(true, animated: true)
        fromVC.endAppearanceTransition()
        toVC.beginAppearanceTransition(false, animated: true)
        toVC.endAppearanceTransition()

        cleanupTransition()
    }

    private func cleanupTransition() {
        stopFrameRateKeepAlive()
        isInteractiveTransition = false
        transitionFromVC = nil
        transitionToVC = nil
        transitionContainerView = nil
    }
}

extension SwipeNavigationController: UIGestureRecognizerDelegate {
    func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
        guard viewControllers.count > 1,
              let pan = gestureRecognizer as? UIPanGestureRecognizer else { return false }

        let velocity = pan.velocity(in: view)
        let isHorizontalSwipeToRight = velocity.x > 0 && abs(velocity.x) > abs(velocity.y)

        return isHorizontalSwipeToRight
    }

    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldBeRequiredToFailBy otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        return otherGestureRecognizer is UIPanGestureRecognizer
    }
}