/*

    Copyright (C) 2016 Apple Inc. All Rights Reserved.

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    The AssetTransitionController class conforms to UINavigationControllerDelegate, UIViewControllerAnimatedTransitioning and UIViewControllerInteractiveTransitioning. 

                This class also manages the gesture recognizer used to initiate the custom interactive pop transition.

*/

import UIKit

let assetTransitionDuration = 0.8

class AssetTransitionController: NSObject {

    weak var navigationController: UINavigationController?

    var operation: UINavigationControllerOperation = .none

    var transitionDriver: AssetTransitionDriver?

    var initiallyInteractive = false

    var panGestureRecognizer: UIPanGestureRecognizer = UIPanGestureRecognizer()

    init(navigationController nc: UINavigationController) {

        navigationController = nc

        super.init()

        nc.delegate = self

        configurePanGestureRecognizer()

    }

    func configurePanGestureRecognizer() {

        panGestureRecognizer.delegate = self

        panGestureRecognizer.maximumNumberOfTouches = 1

        panGestureRecognizer.addTarget(self, action: #selector(initiateTransitionInteractively(_:)))

        navigationController?.view.addGestureRecognizer(panGestureRecognizer)

        guard let interactivePopGestureRecognizer = navigationController?.interactivePopGestureRecognizer else { return }

        panGestureRecognizer.require(toFail: interactivePopGestureRecognizer)

    }

    func initiateTransitionInteractively(_ panGesture: UIPanGestureRecognizer) {

        if panGesture.state == .began && transitionDriver == nil {

            initiallyInteractive = true

            let _ = navigationController?.popViewController(animated: true)

        }

    }

}

extension AssetTransitionController: UIGestureRecognizerDelegate {

    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {

        return true

    }

    func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {

        guard let transitionDriver = self.transitionDriver else {

            let translation = panGestureRecognizer.translation(in: panGestureRecognizer.view)

            let translationIsVertical = (translation.y > 0) && (abs(translation.y) > abs(translation.x))

            return translationIsVertical && (navigationController?.viewControllers.count ?? 0 > 1)

        }

        return transitionDriver.isInteractive

    }

}

extension AssetTransitionController: UINavigationControllerDelegate {

    func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {

        // Remember the direction of the transition (.push or .pop)

        self.operation = operation

        // Return ourselves as the animation controller for the pending transition

        return self

    }

    func navigationController(_ navigationController: UINavigationController, interactionControllerFor animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {

        // Return ourselves as the interaction controller for the pending transition

        return self

    }

}

extension AssetTransitionController: UIViewControllerInteractiveTransitioning {

    func startInteractiveTransition(_ transitionContext: UIViewControllerContextTransitioning) {

        // Create our helper object to manage the transition for the given transitionContext.

        transitionDriver = AssetTransitionDriver(operation: operation, context: transitionContext, panGestureRecognizer: panGestureRecognizer)

    }

    var wantsInteractiveStart: Bool {

        // Determines whether the transition begins in an interactive state

        return initiallyInteractive

    }

}

extension AssetTransitionController: UIViewControllerAnimatedTransitioning {

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

        return assetTransitionDuration

    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {}

    func animationEnded(_ transitionCompleted: Bool) {

        // Clean up our helper object and any additional state

        transitionDriver = nil

        initiallyInteractive = false

        operation = .none

    }

    func interruptibleAnimator(using transitionContext: UIViewControllerContextTransitioning) -> UIViewImplicitlyAnimating {

        // The transition driver (helper object), creates the UIViewPropertyAnimator (transitionAnimator) 

        // to be used for this transition. It must live the lifetime of the transitionContext.

        return (transitionDriver?.transitionAnimator)!

    }

}