Enable picture-in-picture playback for video attachments

Tusker/Info.plist

@@ -81,6 +81,10 @@
 			</array>
 		</dict>
 	</dict>
+	<key>UIBackgroundModes</key>
+	<array>
+		<string>audio</string>
+	</array>
 	<key>UILaunchStoryboardName</key>
 	<string>LaunchScreen</string>
 	<key>UIRequiredDeviceCapabilities</key>

Tusker/Screens/Attachment Gallery/GalleryPlayerViewController.swift

@@ -8,9 +8,18 @@
 
 import UIKit
 import AVKit
+import Pachyderm
 
 class GalleryPlayerViewController: AVPlayerViewController {
 
+    var attachment: Attachment!
+    
+    override func viewDidLoad() {
+        super.viewDidLoad()
+        
+        allowsPictureInPicturePlayback = true
+    }
+    
     override func viewDidAppear(_ animated: Bool) {
         super.viewDidAppear(animated)
         

Tusker/Screens/Attachment Gallery/GalleryViewController.swift

@@ -12,11 +12,13 @@ import AVKit
 
 class GalleryViewController: UIPageViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate, LargeImageAnimatableViewController {
 
+    weak var avPlayerViewControllerDelegate: AVPlayerViewControllerDelegate?
+    
     let attachments: [Attachment]
     let sourceViews: WeakArray<UIImageView>
     let startIndex: Int
     
-    let pages: [UIViewController]
+    var pages: [UIViewController]!
     
     var currentIndex: Int {
         guard let vc = viewControllers?.first,
@@ -72,6 +74,18 @@ class GalleryViewController: UIPageViewController, UIPageViewControllerDataSourc
         self.sourceViews = WeakArray(sourceViews)
         self.startIndex = startIndex
         
+        super.init(transitionStyle: .scroll, navigationOrientation: .horizontal)
+        
+        modalPresentationStyle = .fullScreen
+    }
+    
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+    
+    override func viewDidLoad() {
+        super.viewDidLoad()
+        
         self.pages = attachments.enumerated().map { (index, attachment) in
             switch attachment.kind {
             case .image:
@@ -82,6 +96,8 @@ class GalleryViewController: UIPageViewController, UIPageViewControllerDataSourc
             case .video, .audio:
                 let vc = GalleryPlayerViewController()
                 vc.player = AVPlayer(url: attachment.url)
+                vc.delegate = avPlayerViewControllerDelegate
+                vc.attachment = attachment
                 return vc
             case .gifv:
                 // Passing the source view to the LargeImageGifvContentView is a crappy workaround for not
@@ -101,19 +117,7 @@ class GalleryViewController: UIPageViewController, UIPageViewControllerDataSourc
             }
         }
         
-        super.init(transitionStyle: .scroll, navigationOrientation: .horizontal)
-        
         setViewControllers([pages[startIndex]], direction: .forward, animated: false)
-        
-        modalPresentationStyle = .fullScreen
-    }
-    
-    required init?(coder: NSCoder) {
-        fatalError("init(coder:) has not been implemented")
-    }
-    
-    override func viewDidLoad() {
-        super.viewDidLoad()
 
         self.dataSource = self
         self.delegate = self

Tusker/Views/Attachments/AttachmentView.swift

@@ -12,7 +12,7 @@ import Gifu
 import AVFoundation
 
 protocol AttachmentViewDelegate: class {
-    func attachmentViewGallery(startingAt index: Int) -> UIViewController?
+    func attachmentViewGallery(startingAt index: Int) -> GalleryViewController?
     func attachmentViewPresent(_ vc: UIViewController, animated: Bool)
 }
 

Tusker/Views/Status/BaseStatusTableViewCell.swift

@@ -9,6 +9,7 @@
 import UIKit
 import Pachyderm
 import Combine
+import AVKit
 
 protocol StatusTableViewCellDelegate: TuskerNavigationDelegate {
     func statusCellCollapsedStateChanged(_ cell: BaseStatusTableViewCell)
@@ -70,6 +71,8 @@ class BaseStatusTableViewCell: UITableViewCell {
     private var statusUpdater: Cancellable?
     private var accountUpdater: Cancellable?
     
+    private var currentPictureInPictureVideoStatusID: String?
+    
     override func awakeFromNib() {
         super.awakeFromNib()
         
@@ -360,15 +363,74 @@ class BaseStatusTableViewCell: UITableViewCell {
 }
 
 extension BaseStatusTableViewCell: AttachmentViewDelegate {
-    func attachmentViewGallery(startingAt index: Int) -> UIViewController? {
+    func attachmentViewGallery(startingAt index: Int) -> GalleryViewController? {
         guard let delegate = delegate,
               let status = mastodonController.persistentContainer.status(for: statusID) else { return nil }
         let sourceViews = status.attachments.map(attachmentsView.getAttachmentView(for:))
-        return delegate.gallery(attachments: status.attachments, sourceViews: sourceViews, startIndex: index)
+        let gallery = delegate.gallery(attachments: status.attachments, sourceViews: sourceViews, startIndex: index)
+        gallery.avPlayerViewControllerDelegate = self
+        return gallery
     }
     
     func attachmentViewPresent(_ vc: UIViewController, animated: Bool) {
-        delegate?.show(vc)
+        delegate?.present(vc, animated: animated)
+    }
+}
+
+// todo: This is not ideal. It works when the original cell remains visible and when the cell is reused, but if the cell is dealloc'd
+// resuming from PiP won't work because AVPlayerViewController.delegate is a weak reference.
+extension BaseStatusTableViewCell: AVPlayerViewControllerDelegate {
+    func playerViewControllerWillStartPictureInPicture(_ playerViewController: AVPlayerViewController) {
+        // We need to save the current statusID when PiP is initiated, because if the user restores from PiP after this cell has
+        // been reused, the current value of statusID will not be correct.
+        currentPictureInPictureVideoStatusID = statusID
+    }
+    
+    func playerViewControllerDidStopPictureInPicture(_ playerViewController: AVPlayerViewController) {
+        currentPictureInPictureVideoStatusID = nil
+    }
+    
+    func playerViewControllerShouldAutomaticallyDismissAtPictureInPictureStart(_ playerViewController: AVPlayerViewController) -> Bool {
+        // Ideally, when PiP is automatically initiated by app closing the gallery should not be dismissed
+        // and when PiP is started because the user has tapped the button in the player controls the gallery
+        // gallery should be dismissed. Unfortunately, this doesn't seem to be possible. Instead, the gallery is
+        // always dismissed and is recreated when restoring the interface from PiP.
+        return true
+    }
+    
+    func playerViewController(_ playerViewController: AVPlayerViewController, restoreUserInterfaceForPictureInPictureStopWithCompletionHandler completionHandler: @escaping (Bool) -> Void) {
+        guard let delegate = delegate,
+              let playerViewController = playerViewController as? GalleryPlayerViewController,
+              let id = currentPictureInPictureVideoStatusID,
+              let status = mastodonController.persistentContainer.status(for: id),
+              let index = status.attachments.firstIndex(where: { $0.id == playerViewController.attachment?.id }) else {
+            // returning without invoking completionHandler will dismiss the PiP window
+            return
+        }
+
+        // We create a new gallery view controller starting at the appropriate index and swap the
+        // already-playing VC into the appropriate index so it smoothly continues playing.
+        
+        let sourceViews: [UIImageView?]
+        if self.statusID == id {
+            sourceViews = status.attachments.map(attachmentsView.getAttachmentView(for:))
+        } else {
+            sourceViews = status.attachments.map { (_) in nil }
+        }
+        let gallery = delegate.gallery(attachments: status.attachments, sourceViews: sourceViews, startIndex: index)
+        gallery.avPlayerViewControllerDelegate = self
+        
+        // ensure that all other page VCs are created
+        gallery.loadViewIfNeeded()
+        // replace the newly created player for the same attachment with the already-playing one
+        gallery.pages[index] = playerViewController
+        gallery.setViewControllers([playerViewController], direction: .forward, animated: false, completion: nil)
+
+        // this isn't animated, otherwise the animation plays first and then the PiP window expands
+        // which looks even weirder than the black background appearing instantly and then the PiP window animating
+        delegate.present(gallery, animated: false) {
+            completionHandler(false)
+        }
     }
 }