import UIKit

protocol InteractiveNavigation {
    var presentAnimation: UIViewControllerAnimatedTransitioning? { get }
    var dismissAnimation: UIViewControllerAnimatedTransitioning? { get }
    
    func showNext()
}

enum SwipeDirection: CGFloat, CustomStringConvertible {
    case left  = -1.0
    case none  = 0.0
    case right = 1.0
    
    var description: String {
        switch self {
            case .left: return "Left"
            case .none: return "None"
            case .right: return "Right"
        }
    }
}

class CustomInteractiveAnimationNavigationController: UINavigationController , UIViewControllerTransitioningDelegate, UINavigationControllerDelegate {
    
    // MARK: - Properties
    var interactionController: UIPercentDrivenInteractiveTransition?
    
    // MARK: - View Lifecycle
    override func viewDidLoad() {
        super.viewDidLoad()
        
        transitioningDelegate = self   // for presenting the original navigation controller
        delegate = self                // for navigation controller custom transitions
        
        // Choose one stlye of gesture recognizer
        // Pan Gesture (swipe from/to anywhere on the screen)
        let pan = UIPanGestureRecognizer(target: self, action: #selector(CustomInteractiveAnimationNavigationController.handlePan(_:)))
        view.addGestureRecognizer(pan)
        
        // Edge Pan Gestures (swipe only from either edge)
        let left = UIScreenEdgePanGestureRecognizer(target: self, action: #selector(CustomInteractiveAnimationNavigationController.handleSwipeFromLeft(_:)))
        left.edges = .left
        view.addGestureRecognizer(left);
        
        let right = UIScreenEdgePanGestureRecognizer(target: self, action: #selector(CustomInteractiveAnimationNavigationController.handleSwipeFromRight(_:)))
        right.edges = .right
        view.addGestureRecognizer(right);
    }
    
    
    // MARK: - Gesture Handlers
    func handlePan(_ gesture: UIPanGestureRecognizer) {
        guard let gestureView = gesture.view else {
            return
        }
        
        let flickThreshold: CGFloat = 700.0 // Speed to make transition complete
        let distanceThreshold: CGFloat = 0.3 // Distance to make transition complete
        
        let velocity = gesture.velocity(in: gestureView)
        let translation = gesture.translation(in: gestureView)
        let percent = fabs(translation.x / gestureView.bounds.size.width);
        
        let swipeDirection: SwipeDirection = (velocity.x > 0) ? .right : .left
        
        switch gesture.state {
            case .began:
                interactionController = UIPercentDrivenInteractiveTransition()
                
                if swipeDirection == .right {
                    if viewControllers.count > 1 {
                        popViewController(animated: true)
                    } else {
                        dismiss(animated: true, completion: nil)
                    }
                }
                else {
                    if let currentViewController = viewControllers.last as? InteractiveNavigation {
                        currentViewController.showNext()
                    }
                }
                
            case .changed:
                if let interactionController = self.interactionController {
                    interactionController.update(percent)
                }
                
            case .cancelled:
                if let interactionController = self.interactionController {
                    interactionController.cancel()
                }
                
            case .ended:
                if let interactionController = self.interactionController {
                    if abs(percent) > distanceThreshold || abs(velocity.x) > flickThreshold {
                        interactionController.finish()
                    } else {
                        interactionController.cancel()
                    }
                    
                    self.interactionController = nil
                    swipeDirection = .none
                }
                
            default:
                break
        }
    }

    func handleSwipeFromLeft(_ gesture: UIScreenEdgePanGestureRecognizer) {
        guard let gestureView = gesture.view else {
            return
        }
        
        let percent = gesture.translation(in: gestureView).x / gestureView.bounds.size.width
        
        switch gesture.state {
            case .began:
                interactionController = UIPercentDrivenInteractiveTransition()
                
                if viewControllers.count > 1 {
                    popViewController(animated: true)
                } else {
                    dismiss(animated: true, completion: nil)
            }

            case .changed:
                if let interactionController = self.interactionController {
                    interactionController.update(percent)
                }
            
            case .cancelled:
                if let interactionController = self.interactionController {
                    interactionController.cancel()
                }
            
            case .ended:
                if let interactionController = self.interactionController {
                    if percent > 0.5 {
                        interactionController.finish()
                    } else {
                        interactionController.cancel()
                    }
                    
                    self.interactionController = nil
                }
            
            default:
                break
        }
    }
    
    func handleSwipeFromRight(_ gesture: UIScreenEdgePanGestureRecognizer) {
        guard let gestureView = gesture.view else {
            return
        }
        
        let percent = -gesture.translation(in: gestureView).x / gestureView.bounds.size.width
        
        switch gesture.state {
            case .began:
                if let currentViewController = viewControllers.last as? InteractiveNavigation {
                    interactionController = UIPercentDrivenInteractiveTransition()
                    currentViewController.showNext()
                }

            case .changed:
                if let interactionController = self.interactionController {
                    interactionController.update(percent)
                }
            
            case .cancelled:
                if let interactionController = self.interactionController {
                    interactionController.cancel()
                }
            
            case .ended:
                if let interactionController = self.interactionController {
                    if percent > 0.5 {
                        interactionController.finish()
                    } else {
                        interactionController.cancel()
                    }
                    self.interactionController = nil
                }

            default:
                break
        }
    }
    
    
    // MARK: - UIViewControllerTransitioningDelegate
    func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        guard let _ = presenting as? InteractiveNavigation else {
            return nil
        }
        
        if let currentViewController = viewControllers.last as? InteractiveNavigation {
            return currentViewController.presentAnimation
        }
        
        return nil
    }
    
    func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        guard viewControllers.count != 1 else {
            return nil
        }
        
        if let currentViewController = viewControllers.last as? InteractiveNavigation {
            return currentViewController.dismissAnimation
        }
        return nil
    }
    
    func interactionControllerForPresentation(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactionController
    }
    
    func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactionController
    }
    
    
    // MARK: - UINavigationControllerDelegate
    func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        
        guard operation != .none else {
            return nil
        }
        
        var animation: UIViewControllerAnimatedTransitioning = nil
        
        if let currentViewController = viewControllers.last as? InteractiveNavigation {
            if operation == .push {
                animation = currentViewController.presentAnimation
            }
            else if operation == .pop {
                animation = currentViewController.dismissAnimation
            }
        }
        
        return animation
    }
    
    func navigationController(_ navigationController: UINavigationController, interactionControllerFor animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactionController
    }
}