Add interacting pushing to navigation controllers

Allows people to move forward in the navigation stack after popping
(making popping a non-destructive action).

Tusker.xcodeproj/project.pbxproj

@@ -157,6 +157,8 @@
 		D67C57B221E28FAD00C3118B /* ComposeStatusReplyView.xib in Resources */ = {isa = PBXBuildFile; fileRef = D67C57B121E28FAD00C3118B /* ComposeStatusReplyView.xib */; };
 		D67C57B421E2910700C3118B /* ComposeStatusReplyView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D67C57B321E2910700C3118B /* ComposeStatusReplyView.swift */; };
 		D68FEC4F232C5BC300C84F23 /* SegmentedPageViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D68FEC4E232C5BC300C84F23 /* SegmentedPageViewController.swift */; };
+		D693DE5723FE1A6A0061E07D /* EnhancedNavigationViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D693DE5623FE1A6A0061E07D /* EnhancedNavigationViewController.swift */; };
+		D693DE5923FE24310061E07D /* InteractivePushTransition.swift in Sources */ = {isa = PBXBuildFile; fileRef = D693DE5823FE24300061E07D /* InteractivePushTransition.swift */; };
 		D6945C2F23AC47C3005C403C /* SavedDataManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6945C2E23AC47C3005C403C /* SavedDataManager.swift */; };
 		D6945C3223AC4D36005C403C /* HashtagTimelineViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6945C3123AC4D36005C403C /* HashtagTimelineViewController.swift */; };
 		D6945C3423AC6431005C403C /* AddSavedHashtagViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6945C3323AC6431005C403C /* AddSavedHashtagViewController.swift */; };
@@ -432,6 +434,8 @@
 		D67C57B121E28FAD00C3118B /* ComposeStatusReplyView.xib */ = {isa = PBXFileReference; lastKnownFileType = file.xib; path = ComposeStatusReplyView.xib; sourceTree = "<group>"; };
 		D67C57B321E2910700C3118B /* ComposeStatusReplyView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ComposeStatusReplyView.swift; sourceTree = "<group>"; };
 		D68FEC4E232C5BC300C84F23 /* SegmentedPageViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SegmentedPageViewController.swift; sourceTree = "<group>"; };
+		D693DE5623FE1A6A0061E07D /* EnhancedNavigationViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EnhancedNavigationViewController.swift; sourceTree = "<group>"; };
+		D693DE5823FE24300061E07D /* InteractivePushTransition.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InteractivePushTransition.swift; sourceTree = "<group>"; };
 		D6945C2E23AC47C3005C403C /* SavedDataManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SavedDataManager.swift; sourceTree = "<group>"; };
 		D6945C3123AC4D36005C403C /* HashtagTimelineViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = HashtagTimelineViewController.swift; sourceTree = "<group>"; };
 		D6945C3323AC6431005C403C /* AddSavedHashtagViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AddSavedHashtagViewController.swift; sourceTree = "<group>"; };
@@ -1136,6 +1140,8 @@
 				D6B8DB332182A59300424AF7 /* UIAlertController+Visibility.swift */,
 				D6BC8747219738E1006163F1 /* EnhancedTableViewController.swift */,
 				D68FEC4E232C5BC300C84F23 /* SegmentedPageViewController.swift */,
+				D693DE5623FE1A6A0061E07D /* EnhancedNavigationViewController.swift */,
+				D693DE5823FE24300061E07D /* InteractivePushTransition.swift */,
 			);
 			path = Utilities;
 			sourceTree = "<group>";
@@ -1584,6 +1590,7 @@
 				D6BC9DB3232D4C07002CA326 /* WellnessPrefsView.swift in Sources */,
 				0454DDAF22B462EF00B8BB8E /* GalleryExpandAnimationController.swift in Sources */,
 				D64BC18F23C18B9D000D0238 /* FollowRequestNotificationTableViewCell.swift in Sources */,
+				D693DE5923FE24310061E07D /* InteractivePushTransition.swift in Sources */,
 				D6A3BC8A2321F79B00FD64D5 /* AccountTableViewCell.swift in Sources */,
 				D66A77BB233838DC0058F1EC /* UIFont+Traits.swift in Sources */,
 				D68FEC4F232C5BC300C84F23 /* SegmentedPageViewController.swift in Sources */,
@@ -1698,6 +1705,7 @@
 				D667E5E721349D4C0057A976 /* ProfileTableViewController.swift in Sources */,
 				D6D4DDD0212518A000E1C4BB /* AppDelegate.swift in Sources */,
 				D6B053A423BD2C8100A066FA /* AssetCollectionsListViewController.swift in Sources */,
+				D693DE5723FE1A6A0061E07D /* EnhancedNavigationViewController.swift in Sources */,
 				D6163F2C21AA0AF1008DAC41 /* MyProfileTableViewController.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;

Tusker/Screens/Main/MainTabBarViewController.swift

@@ -48,7 +48,7 @@ class MainTabBarViewController: UITabBarController, UITabBarControllerDelegate {
         if let vc = vc as? UINavigationController {
             return vc
         } else {
-            return UINavigationController(rootViewController: vc)
+            return EnhancedNavigationViewController(rootViewController: vc)
         }
     }
     

Tusker/Screens/Utilities/EnhancedNavigationViewController.swift

@@ -0,0 +1,76 @@
+//
+//  EnhancedNavigationViewController.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 2/19/20.
+//  Copyright © 2020 Shadowfacts. All rights reserved.
+//
+
+import UIKit
+
+class EnhancedNavigationViewController: UINavigationController {
+
+    var poppedViewControllers = [UIViewController]()
+    var skipResetPoppedOnNextPush = false
+    
+    private var interactivePushTransition: InteractivePushTransition!
+    
+    override func viewDidLoad() {
+        super.viewDidLoad()
+
+        self.interactivePushTransition = InteractivePushTransition(navigationController: self)
+    }
+    
+    override func popViewController(animated: Bool) -> UIViewController? {
+        if let popped = super.popViewController(animated: animated) {
+            poppedViewControllers.insert(popped, at: 0)
+            return popped
+        } else {
+            return nil
+        }
+    }
+    
+    override func popToRootViewController(animated: Bool) -> [UIViewController]? {
+        if let popped = super.popToRootViewController(animated: animated) {
+            poppedViewControllers = popped
+            return popped
+        } else {
+            return nil
+        }
+    }
+    
+    override func popToViewController(_ viewController: UIViewController, animated: Bool) -> [UIViewController]? {
+        if let popped = super.popToViewController(viewController, animated: animated) {
+            poppedViewControllers.insert(contentsOf: popped, at: 0)
+            return popped
+        } else {
+            return nil
+        }
+    }
+    
+    override func pushViewController(_ viewController: UIViewController, animated: Bool) {
+        if skipResetPoppedOnNextPush {
+            skipResetPoppedOnNextPush = false
+        } else {
+            self.poppedViewControllers = []
+        }
+        super.pushViewController(viewController, animated: animated)
+    }
+    
+    func onWillShow() {
+        self.transitionCoordinator?.notifyWhenInteractionChanges({ (context) in
+            if context.isCancelled {
+                if self.interactivePushTransition.interactive {
+                    // when an interactive push gesture is cancelled, make sure to adding the VC that was being pushed back onto the popped stack so it doesn't disappear
+                    self.poppedViewControllers.insert(self.interactivePushTransition.pushingViewController!, at: 0)
+                } else {
+                    // when an interactive pop gesture is cancelled (i.e. the user lifts their finger before it triggers),
+                    // the popViewController(animated:) method has already been called so the VC has already been added to the popped stack
+                    // so we make sure to remove it, otherwise there could be duplicate VCs on the navigation stasck
+                    self.poppedViewControllers.remove(at: 0)
+                }
+            }
+        })
+    }
+
+}

Tusker/Screens/Utilities/InteractivePushTransition.swift

@@ -0,0 +1,139 @@
+//
+//  InteractivePushTransition.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 2/19/20.
+//  Copyright © 2020 Shadowfacts. All rights reserved.
+//
+
+import UIKit
+
+/// Allows interactively moving forward through the navigation stack after popping
+/// Based on https://github.com/NSExceptional/TBInteractivePushTransition
+class InteractivePushTransition: UIPercentDrivenInteractiveTransition {
+    
+    fileprivate let minimumPushVelocityThreshold: CGFloat = 700
+    fileprivate let minimumPushDistanceThreshold: CGFloat = 0.5
+    fileprivate let pushAnimationDuration: TimeInterval = 0.35
+    
+    private(set) weak var navigationController: EnhancedNavigationViewController!
+
+    private(set) weak var interactivePushGestureRecognizer: UIScreenEdgePanGestureRecognizer!
+    
+    private(set) var interactive = false
+    private(set) weak var pushingViewController: UIViewController?
+    
+    init(navigationController: EnhancedNavigationViewController) {
+        super.init()
+        
+        self.navigationController = navigationController
+
+        let interactivePushGestureRecognizer = UIScreenEdgePanGestureRecognizer(target: self, action: #selector(handleSwipeForward(_:)))
+        self.interactivePushGestureRecognizer = interactivePushGestureRecognizer
+        
+        navigationController.delegate = self
+        interactivePushGestureRecognizer.edges = .right
+        interactivePushGestureRecognizer.require(toFail: navigationController.interactivePopGestureRecognizer!)
+        navigationController.view.addGestureRecognizer(interactivePushGestureRecognizer)
+    }
+
+    @objc func handleSwipeForward(_ recognizer: UIPanGestureRecognizer) {
+        interactive = true
+        
+        let velocity = recognizer.velocity(in: recognizer.view)
+        let translation = recognizer.translation(in: recognizer.view)
+        let dx = -translation.x / navigationController.view.bounds.width
+        let vx = -velocity.x
+        
+        switch recognizer.state {
+        case .began:
+            if let viewController = navigationController.poppedViewControllers.first {
+                pushingViewController = viewController
+                navigationController.poppedViewControllers.removeFirst()
+                navigationController.skipResetPoppedOnNextPush = true
+                navigationController.pushViewController(viewController, animated: true)
+            } else {
+                interactive = false
+            }
+            
+        case .changed:
+            update(dx)
+
+        case .ended:
+            if (dx > minimumPushDistanceThreshold || vx > minimumPushVelocityThreshold) {
+                finish()
+            } else {
+                cancel()
+            }
+            interactive = false
+            
+        default:
+            cancel()
+            interactive = false
+        }
+    }
+
+}
+
+extension InteractivePushTransition: UINavigationControllerDelegate {
+    func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {
+        self.navigationController.onWillShow()
+    }
+    
+    func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationController.Operation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
+        if operation == .push, interactive {
+            return self
+        }
+        
+        return nil
+    }
+    
+    func navigationController(_ navigationController: UINavigationController, interactionControllerFor animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
+        if interactive {
+            return self
+        }
+        return nil
+    }
+}
+
+extension InteractivePushTransition: UIViewControllerAnimatedTransitioning {
+    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
+        return pushAnimationDuration
+    }
+    
+    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
+        let toView = transitionContext.view(forKey: .to)!
+        let fromView = transitionContext.view(forKey: .from)!
+
+        let dimmingView = UIView()
+        dimmingView.backgroundColor = .black
+        dimmingView.alpha = 0
+        dimmingView.frame = fromView.frame
+
+        transitionContext.containerView.addSubview(dimmingView)
+        transitionContext.containerView.addSubview(toView)
+        
+        // modify frame of presented view to go from x = <screen width> to x = 0
+        var frame = fromView.frame
+        frame.origin.x = frame.width
+        toView.frame = frame
+        frame.origin.x = 0
+        
+        // we want it linear while interactive, but we want the "ease out" animation
+        // if the user flicks the screen ahrd enough to finish the transition without interaction
+        let options = interactive ? UIView.AnimationOptions.curveLinear : .curveEaseOut
+        
+        let duration = transitionDuration(using: transitionContext)
+        UIView.animate(withDuration: duration, delay: 0, options: options, animations: {
+            // these magic numbers scientifically determined by repeatedly adjusting and comparing to the system animation
+            let translationDistance = -frame.size.width * 0.3
+            fromView.transform = CGAffineTransform(translationX: translationDistance, y: 0)
+            toView.frame = frame
+            dimmingView.alpha = 0.075
+        }) { (finished) in
+            fromView.transform = .identity
+            dimmingView.removeFromSuperview()
+            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
+        }
+    }
+}