import UIKit

class DetailViewController: UIViewController, UIGestureRecognizerDelegate {
    
    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
        self.hidesBottomBarWhenPushed = true
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        self.hidesBottomBarWhenPushed = true
    }
    
    let panGestureRecognizer = UIPanGestureRecognizer.init()

    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = .lightGray
        
        panGestureRecognizer.addTarget(self, action: #selector(panGestureRecognizerAction(_:)))
        panGestureRecognizer.delegate = self
        view.addGestureRecognizer(panGestureRecognizer);
        
        guard let navigationController = navigationController else { return }
        
        let title = "Detail Page \(navigationController.viewControllers.count)"
        self.navigationItem.title = title;
        
        let textLabel = UILabel.init();
        textLabel.autoresizingMask = [.flexibleTopMargin, .flexibleLeftMargin, .flexibleBottomMargin, .flexibleRightMargin]
        textLabel.textAlignment    = .center;
        textLabel.backgroundColor  = .init(white: 0.95, alpha: 1.0)
        textLabel.textColor        = UIColor.black;
        textLabel.font             = UIFont.monospacedSystemFont(ofSize: 32.0, weight: .bold)
        textLabel.text             = title
        textLabel.sizeToFit()
        
        let bounds = self.view.bounds;
        var frame = textLabel.frame;
        frame.size.width += 40.0;
        frame.size.height += 40.0;
        frame.origin.x = (bounds.width - frame.width) * 0.5;
        frame.origin.y = (bounds.height - frame.height) * 0.5;
        textLabel.frame = frame;
        view.addSubview(textLabel);
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        guard let navigationController = navigationController else { return }
        navigationController.delegate = self;
        navigationController.interactivePopGestureRecognizer?.isEnabled = false
        navigationController.interactiveContentPopGestureRecognizer?.isEnabled = false
        
        navigationController.interactivePopGestureRecognizer?.require(toFail: panGestureRecognizer)
        navigationController.interactiveContentPopGestureRecognizer?.require(toFail: panGestureRecognizer)
    }
    
    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
    }
    
    private var animationController: UIViewControllerAnimatedTransitioning?
    private let interactionController = UIPercentDrivenInteractiveTransition()
    
    @objc func panGestureRecognizerAction(_ sender: UIPanGestureRecognizer) {
        switch sender.state {
        case .possible:
            break
        case .began:
            break
        case .changed:
            let s = self.view.frame.height;
            
            let d = sender.translation(in: nil).y;
            
            if animationController is HideAnimationController {
                self.interactionController.update(max(0, d / s))
            } else {
                self.interactionController.update(max(0, -d / s))
            }
            break
        case .ended:
            fallthrough
        case .cancelled:
            fallthrough
        case .failed:
            let s = self.view.frame.height;
            
            let d = sender.translation(in: nil).y;
            let v = sender.velocity(in: nil)
            
            let p = animationController is HideAnimationController ? max(0, d / s) : max(0, -d / s)
            
            if p > 0.5 || v.y > 500 || v.y < -500 {
                self.interactionController.finish()
            } else {
                self.interactionController.cancel()
            }
            
            self.animationController = nil;
            break
        case .recognized:
            fallthrough
        default:
            break
        }
    }

    func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
        guard animationController == nil else { return false }
        guard let navigationController = navigationController else { return false }
        guard let pan = gestureRecognizer as? UIPanGestureRecognizer else { return false }
        let translation = pan.translation(in: nil)
        let velocity = pan.velocity(in: nil)
        
        print("gestureRecognizerShouldBegin: translation = \(translation), velocity = \(velocity)")
        
        guard abs(translation.x) <= 0.1 || (translation.y / translation.x) > 3.0 else {
            return false
        }
        
        if translation.y > 0 {
            if navigationController.viewControllers.count <= 1 {
                return false
            }
            self.animationController = HideAnimationController()
            navigationController.popViewController(animated: true)
        } else {
            self.animationController = ShowAnimationController()
            self.interactionController.update(0)
            let viewController = DetailViewController.init()
            navigationController.pushViewController(viewController, animated: true)
        }
        
        return true
    }

}

extension DetailViewController : UINavigationControllerDelegate {
    
    func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationController.Operation, from fromVC: UIViewController, to toVC: UIViewController) -> (any UIViewControllerAnimatedTransitioning)? {
        // driven by gesture
        if let animationController = self.animationController {
            return animationController
        }
        
        // normal
        switch operation {
        case .push:
            return ShowAnimationController.init()
        case .pop:
            return HideAnimationController.init()
        default:
            return nil
        }
    }
    
    func navigationController(_ navigationController: UINavigationController, interactionControllerFor animationController: any UIViewControllerAnimatedTransitioning) -> (any UIViewControllerInteractiveTransitioning)? {
        if self.animationController?.isEqual(animationController) == true {
            return self.interactionController;
        }
        return nil
    }
    
}

// pop
private class HideAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
    
    func transitionDuration(using transitionContext: (any UIViewControllerContextTransitioning)?) -> TimeInterval {
        return 0.35
    }
    
    func animateTransition(using transitionContext: any UIViewControllerContextTransitioning) {
        let containerView = transitionContext.containerView
        
        let fromView = transitionContext.view(forKey: .from)!
        let toView = transitionContext.view(forKey: .to)!
        
        let frame = fromView.frame;
        
        toView.frame = frame.offsetBy(dx: 0, dy: -frame.height)
        containerView.insertSubview(toView, belowSubview: fromView)

        let duration = self.transitionDuration(using: transitionContext)
        
        UIView.animate(withDuration: duration) {
            fromView.frame = frame.offsetBy(dx: 0, dy: frame.height)
            toView.frame = frame
        } completion: { _ in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
    }
    
}

// push
private class ShowAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
    
    func transitionDuration(using transitionContext: (any UIViewControllerContextTransitioning)?) -> TimeInterval {
        return 0.35
    }
    
    func animateTransition(using transitionContext: any UIViewControllerContextTransitioning) {
        let containerView = transitionContext.containerView
        
        let fromView = transitionContext.view(forKey: .from)!
        let toView = transitionContext.view(forKey: .to)!
         
        let frame = fromView.frame;
        
        toView.frame = frame.offsetBy(dx: 0, dy: frame.height)
        containerView.addSubview(toView)

        let duration = self.transitionDuration(using: transitionContext)
        
        UIView.animate(withDuration: duration) {
            fromView.frame = frame.offsetBy(dx: 0, dy: -frame.height)
            toView.frame = frame
        } completion: { _ in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
    }
    
}