Fix gifv playback not continuing when returning from background

Closes #506

Tusker.xcodeproj/project.pbxproj

@@ -361,6 +361,7 @@
 		D6EBF01523C55C0900AE061B /* UIApplication+Scenes.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6EBF01423C55C0900AE061B /* UIApplication+Scenes.swift */; };
 		D6EBF01723C55E0D00AE061B /* UISceneSession+MastodonController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6EBF01623C55E0D00AE061B /* UISceneSession+MastodonController.swift */; };
 		D6EE63FB2551F7F60065485C /* StatusCollapseButton.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6EE63FA2551F7F60065485C /* StatusCollapseButton.swift */; };
+		D6EEDE932C3CF21800E10E51 /* AudioSessionCoordinator.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6EEDE922C3CF21800E10E51 /* AudioSessionCoordinator.swift */; };
 		D6F0B12B24A3071C001E48C3 /* MainSplitViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6F0B12A24A3071C001E48C3 /* MainSplitViewController.swift */; };
 		D6F0B17524A3A1AA001E48C3 /* MainSidebarViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6F0B17424A3A1AA001E48C3 /* MainSidebarViewController.swift */; };
 		D6F253CF2AC9F86300806D83 /* SearchTokenSuggestionCollectionViewCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6F253CE2AC9F86300806D83 /* SearchTokenSuggestionCollectionViewCell.swift */; };
@@ -803,6 +804,7 @@
 		D6EBF01423C55C0900AE061B /* UIApplication+Scenes.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "UIApplication+Scenes.swift"; sourceTree = "<group>"; };
 		D6EBF01623C55E0D00AE061B /* UISceneSession+MastodonController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "UISceneSession+MastodonController.swift"; sourceTree = "<group>"; };
 		D6EE63FA2551F7F60065485C /* StatusCollapseButton.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StatusCollapseButton.swift; sourceTree = "<group>"; };
+		D6EEDE922C3CF21800E10E51 /* AudioSessionCoordinator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AudioSessionCoordinator.swift; sourceTree = "<group>"; };
 		D6F0B12A24A3071C001E48C3 /* MainSplitViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MainSplitViewController.swift; sourceTree = "<group>"; };
 		D6F0B17424A3A1AA001E48C3 /* MainSidebarViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MainSidebarViewController.swift; sourceTree = "<group>"; };
 		D6F253CE2AC9F86300806D83 /* SearchTokenSuggestionCollectionViewCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SearchTokenSuggestionCollectionViewCell.swift; sourceTree = "<group>"; };
@@ -1607,6 +1609,7 @@
 				D691296D2BA75ACF005C58ED /* PrivacyInfo.xcprivacy */,
 				D671A6BE299DA96100A81FEA /* Tusker-Bridging-Header.h */,
 				D6D4DDCF212518A000E1C4BB /* AppDelegate.swift */,
+				D6EEDE922C3CF21800E10E51 /* AudioSessionCoordinator.swift */,
 				D6D79F582A13293200AB2315 /* BackgroundManager.swift */,
 				D69261262BB3BA610023152C /* Box.swift */,
 				D61F75B6293C119700C0B37F /* Filterer.swift */,
@@ -2147,6 +2150,7 @@
 				D61F759B29384F9C00C0B37F /* FilterMO.swift in Sources */,
 				D68FEC4F232C5BC300C84F23 /* SegmentedPageViewController.swift in Sources */,
 				D6934F342BA8D65A002B1C8D /* ImageGalleryDataSource.swift in Sources */,
+				D6EEDE932C3CF21800E10E51 /* AudioSessionCoordinator.swift in Sources */,
 				D6C4532D2BCB86AC00E26A0E /* AppearancePrefsView.swift in Sources */,
 				D64AAE9126C80DC600FC57FB /* ToastView.swift in Sources */,
 				D6BC74862AFC4772000DD603 /* SuggestedProfileCardView.swift in Sources */,

Tusker/AudioSessionCoordinator.swift

@@ -0,0 +1,87 @@
+//
+//  AudioSessionCoordinator.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 7/8/24.
+//  Copyright © 2024 Shadowfacts. All rights reserved.
+//
+
+import Foundation
+import AVFoundation
+
+final class AudioSessionCoordinator {
+    static let shared = AudioSessionCoordinator()
+    
+    private init() {}
+    
+    private let queue = DispatchQueue(label: "AudioSessionCoordinator", qos: .userInitiated)
+    
+    private var videoCount = 0
+    private var gifvCount = 0
+    
+    func beginPlayback(mode: Mode, completionHandler: (() -> Void)? = nil) -> Token {
+        let token = Token(mode: mode)
+        queue.async {
+            switch mode {
+            case .video:
+                self.videoCount += 1
+            case .gifv:
+                self.gifvCount += 1
+            }
+            self.update(completionHandler: completionHandler)
+        }
+        return token
+    }
+    
+    func endPlayback(token: Token, completionHandler: (() -> Void)? = nil) {
+        // the enqueued block can't retain token, since it may be being dealloc'd right now
+        let mode = token.mode
+        queue.async {
+            switch mode {
+            case .video:
+                self.videoCount -= 1
+            case .gifv:
+                self.gifvCount -= 1
+            }
+            self.update(completionHandler: completionHandler)
+        }
+    }
+    
+    private func update(completionHandler: (() -> Void)?) {
+        let currentCategory = AVAudioSession.sharedInstance().category
+        if videoCount > 0 {
+            try? AVAudioSession.sharedInstance().setCategory(.playback)
+            try? AVAudioSession.sharedInstance().setActive(true)
+        } else if gifvCount > 0 {
+            // if we're transitioning from video to gifv, fully deactivate first
+            // in order to let other (music) apps resume, then activate with the
+            // ambient category to "mix" with others
+            if currentCategory == .playback {
+                try? AVAudioSession.sharedInstance().setActive(false, options: .notifyOthersOnDeactivation)
+            }
+            // only gifv modes requested, allow mixing with others
+            try? AVAudioSession.sharedInstance().setCategory(.ambient)
+            try? AVAudioSession.sharedInstance().setActive(true)
+        } else {
+            try? AVAudioSession.sharedInstance().setActive(false, options: .notifyOthersOnDeactivation)
+        }
+        completionHandler?()
+    }
+    
+    final class Token {
+        let mode: Mode
+        
+        init(mode: Mode) {
+            self.mode = mode
+        }
+        
+        deinit {
+            AudioSessionCoordinator.shared.endPlayback(token: self)
+        }
+    }
+    
+    enum Mode {
+        case video
+        case gifv
+    }
+}

Tusker/Screens/Gallery/VideoGalleryContentViewController.swift

@@ -29,6 +29,7 @@ class VideoGalleryContentViewController: UIViewController, GalleryContentViewCon
     private var rateObservation: NSKeyValueObservation?
     private var isFirstAppearance = true
     private var hideControlsWorkItem: DispatchWorkItem?
+    private var audioSessionToken: AudioSessionCoordinator.Token?
     
     init(url: URL, caption: String?) {
         self.url = url
@@ -172,10 +173,7 @@ class VideoGalleryContentViewController: UIViewController, GalleryContentViewCon
         let wasFirstAppearance = isFirstAppearance
         isFirstAppearance = false
         
-        DispatchQueue.global(qos: .userInitiated).async {
-            try? AVAudioSession.sharedInstance().setCategory(.playback)
-            try? AVAudioSession.sharedInstance().setActive(true)
-            
+        audioSessionToken = AudioSessionCoordinator.shared.beginPlayback(mode: .video) {
             if wasFirstAppearance {
                 DispatchQueue.main.async {
                     self.player.play()
@@ -187,8 +185,8 @@ class VideoGalleryContentViewController: UIViewController, GalleryContentViewCon
     func galleryContentWillDisappear() {
         player.pause()
         
-        DispatchQueue.global(qos: .userInitiated).async {
-            try? AVAudioSession.sharedInstance().setActive(false, options: .notifyOthersOnDeactivation)
+        if let audioSessionToken {
+            AudioSessionCoordinator.shared.endPlayback(token: audioSessionToken)
         }
     }
     

Tusker/Views/Attachments/GifvController.swift

@@ -17,6 +17,7 @@ class GifvController {
     let player: AVPlayer
     
     private var isGrayscale = false
+    private var audioSessionToken: AudioSessionCoordinator.Token?
     
     let presentationSizeSubject = PassthroughSubject<CGSize, Never>()
     private var presentationSizeObservation: NSKeyValueObservation?
@@ -29,7 +30,9 @@ class GifvController {
         self.isGrayscale = Preferences.shared.grayscaleImages
         
         player.isMuted = true
-        #if !os(visionOS)
+        #if os(visionOS)
+        player.preventsAutomaticBackgroundingDuringVideoPlayback = false
+        #else
         player.preventsDisplaySleepDuringVideoPlayback = false
         #endif
         
@@ -41,12 +44,19 @@ class GifvController {
     
     func play() {
         if player.rate == 0 {
-            player.play()
+            audioSessionToken = AudioSessionCoordinator.shared.beginPlayback(mode: .gifv) {
+                DispatchQueue.main.async {
+                    self.player.play()
+                }
+            }
         }
     }
     
     func pause() {
         player.pause()
+        if let audioSessionToken {
+            AudioSessionCoordinator.shared.endPlayback(token: audioSessionToken)
+        }
     }
     
     private func updatePresentationSizeObservation() {

Tusker/Views/Attachments/GifvPlayerView.swift

@@ -22,6 +22,7 @@ class GifvPlayerView: UIView {
 
     let controller: GifvController
     private var presentationSizeCancellable: AnyCancellable?
+    private var wasPlayingWhenSceneBackgrounded = false
     
     override var intrinsicContentSize: CGSize {
         controller.item.presentationSize
@@ -45,4 +46,30 @@ class GifvPlayerView: UIView {
         fatalError("init(coder:) has not been implemented")
     }
     
+    override func willMove(toWindow newWindow: UIWindow?) {
+        super.willMove(toWindow: newWindow)
+        
+        if let oldWindow = window,
+           let oldScene = oldWindow.windowScene {
+            NotificationCenter.default.removeObserver(self, name: UIScene.didEnterBackgroundNotification, object: oldScene)
+            NotificationCenter.default.removeObserver(self, name: UIScene.willEnterForegroundNotification, object: oldScene)
+        }
+        
+        if let newWindow,
+           let newScene = newWindow.windowScene {
+            NotificationCenter.default.addObserver(self, selector: #selector(sceneDidEnterBackground), name: UIScene.didEnterBackgroundNotification, object: newScene)
+            NotificationCenter.default.addObserver(self, selector: #selector(sceneWillEnterForeground), name: UIScene.willEnterForegroundNotification, object: newScene)
+        }
+    }
+    
+    @objc private func sceneDidEnterBackground() {
+        wasPlayingWhenSceneBackgrounded = controller.player.rate > 0
+    }
+    
+    @objc private func sceneWillEnterForeground() {
+        if wasPlayingWhenSceneBackgrounded {
+            controller.play()
+        }
+    }
+    
 }

Tusker/Weak.swift

@@ -8,7 +8,7 @@
 
 import Foundation
 
-class WeakHolder<T: AnyObject> {
+final class WeakHolder<T: AnyObject> {
     weak var object: T?
     
     init(_ object: T?) {
@@ -16,7 +16,7 @@ class WeakHolder<T: AnyObject> {
     }
 }
 
-struct WeakArray<Element: AnyObject>: MutableCollection, RangeReplaceableCollection {
+struct WeakArray<Element: AnyObject>: MutableCollection, RangeReplaceableCollection, RandomAccessCollection, BidirectionalCollection {
     private var array: [WeakHolder<Element>]
     
     var startIndex: Int { array.startIndex }
@@ -47,6 +47,10 @@ struct WeakArray<Element: AnyObject>: MutableCollection, RangeReplaceableCollect
         return array.index(after: i)
     }
     
+    func index(before i: Int) -> Int {
+        return array.index(before: i)
+    }
+    
     mutating func replaceSubrange<C>(_ subrange: Range<Int>, with newElements: C) where C : Collection, Self.Element == C.Element {
         array.replaceSubrange(subrange, with: newElements.map { WeakHolder($0) })
     }