Initial implementation of profile switching with collection views

Tusker.xcodeproj/project.pbxproj

@@ -36,13 +36,15 @@
 		D61A45E828DF477D002BE511 /* LoadingCollectionViewCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61A45E728DF477D002BE511 /* LoadingCollectionViewCell.swift */; };
 		D61A45EA28DF51EE002BE511 /* TimelineLikeCollectionViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61A45E928DF51EE002BE511 /* TimelineLikeCollectionViewController.swift */; };
 		D61ABEF628EE74D400B29151 /* StatusCollectionViewCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61ABEF528EE74D400B29151 /* StatusCollectionViewCell.swift */; };
+		D61ABEF828EFC3F900B29151 /* NewProfileStatusesViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61ABEF728EFC3F900B29151 /* NewProfileStatusesViewController.swift */; };
 		D61ABEFC28F105DE00B29151 /* Pachyderm in Frameworks */ = {isa = PBXBuildFile; productRef = D61ABEFB28F105DE00B29151 /* Pachyderm */; };
 		D61ABEFE28F1C92600B29151 /* FavoriteService.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61ABEFD28F1C92600B29151 /* FavoriteService.swift */; };
-		D61ABEF828EFC3F900B29151 /* NewProfileStatusesViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61ABEF728EFC3F900B29151 /* NewProfileStatusesViewController.swift */; };
 		D61AC1D5232E9FA600C54D2D /* InstanceSelectorTableViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61AC1D4232E9FA600C54D2D /* InstanceSelectorTableViewController.swift */; };
 		D61AC1D8232EA42D00C54D2D /* InstanceTableViewCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61AC1D6232EA42D00C54D2D /* InstanceTableViewCell.swift */; };
 		D61AC1D9232EA42D00C54D2D /* InstanceTableViewCell.xib in Resources */ = {isa = PBXBuildFile; fileRef = D61AC1D7232EA42D00C54D2D /* InstanceTableViewCell.xib */; };
 		D61DC84628F498F200B82C6E /* Logging.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61DC84528F498F200B82C6E /* Logging.swift */; };
+		D61DC84B28F4FD2000B82C6E /* NewProfileHeaderCollectionViewCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61DC84A28F4FD2000B82C6E /* NewProfileHeaderCollectionViewCell.swift */; };
+		D61DC84D28F500D200B82C6E /* NewProfileViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D61DC84C28F500D200B82C6E /* NewProfileViewController.swift */; };
 		D620483423D3801D008A63EF /* LinkTextView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D620483323D3801D008A63EF /* LinkTextView.swift */; };
 		D620483623D38075008A63EF /* ContentTextView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D620483523D38075008A63EF /* ContentTextView.swift */; };
 		D620483823D38190008A63EF /* StatusContentTextView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D620483723D38190008A63EF /* StatusContentTextView.swift */; };
@@ -390,12 +392,14 @@
 		D61A45E728DF477D002BE511 /* LoadingCollectionViewCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LoadingCollectionViewCell.swift; sourceTree = "<group>"; };
 		D61A45E928DF51EE002BE511 /* TimelineLikeCollectionViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TimelineLikeCollectionViewController.swift; sourceTree = "<group>"; };
 		D61ABEF528EE74D400B29151 /* StatusCollectionViewCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StatusCollectionViewCell.swift; sourceTree = "<group>"; };
-		D61ABEFD28F1C92600B29151 /* FavoriteService.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FavoriteService.swift; sourceTree = "<group>"; };
 		D61ABEF728EFC3F900B29151 /* NewProfileStatusesViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NewProfileStatusesViewController.swift; sourceTree = "<group>"; };
+		D61ABEFD28F1C92600B29151 /* FavoriteService.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FavoriteService.swift; sourceTree = "<group>"; };
 		D61AC1D4232E9FA600C54D2D /* InstanceSelectorTableViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InstanceSelectorTableViewController.swift; sourceTree = "<group>"; };
 		D61AC1D6232EA42D00C54D2D /* InstanceTableViewCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InstanceTableViewCell.swift; sourceTree = "<group>"; };
 		D61AC1D7232EA42D00C54D2D /* InstanceTableViewCell.xib */ = {isa = PBXFileReference; lastKnownFileType = file.xib; path = InstanceTableViewCell.xib; sourceTree = "<group>"; };
 		D61DC84528F498F200B82C6E /* Logging.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Logging.swift; sourceTree = "<group>"; };
+		D61DC84A28F4FD2000B82C6E /* NewProfileHeaderCollectionViewCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NewProfileHeaderCollectionViewCell.swift; sourceTree = "<group>"; };
+		D61DC84C28F500D200B82C6E /* NewProfileViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NewProfileViewController.swift; sourceTree = "<group>"; };
 		D620483323D3801D008A63EF /* LinkTextView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LinkTextView.swift; sourceTree = "<group>"; };
 		D620483523D38075008A63EF /* ContentTextView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ContentTextView.swift; sourceTree = "<group>"; };
 		D620483723D38190008A63EF /* StatusContentTextView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StatusContentTextView.swift; sourceTree = "<group>"; };
@@ -946,7 +950,9 @@
 				D6412B0424B0227D00F5412E /* ProfileViewController.swift */,
 				D63A8D0A2561C27F00D9DFFF /* ProfileStatusesViewController.swift */,
 				D6412B0824B0291E00F5412E /* MyProfileViewController.swift */,
+				D61DC84C28F500D200B82C6E /* NewProfileViewController.swift */,
 				D61ABEF728EFC3F900B29151 /* NewProfileStatusesViewController.swift */,
+				D61DC84A28F4FD2000B82C6E /* NewProfileHeaderCollectionViewCell.swift */,
 			);
 			path = Profile;
 			sourceTree = "<group>";
@@ -1832,6 +1838,7 @@
 				D681E4D5246E2BC30053414F /* UnmuteConversationActivity.swift in Sources */,
 				D6B4A4FF2506B81A000C81C1 /* AccountDisplayNameLabel.swift in Sources */,
 				D63D8DF42850FE7A008D95E1 /* ViewTags.swift in Sources */,
+				D61DC84B28F4FD2000B82C6E /* NewProfileHeaderCollectionViewCell.swift in Sources */,
 				D6B053A623BD2D0C00A066FA /* AssetCollectionViewController.swift in Sources */,
 				D61A45E828DF477D002BE511 /* LoadingCollectionViewCell.swift in Sources */,
 				D67B506D250B291200FAECFB /* BlurHashDecode.swift in Sources */,
@@ -1858,6 +1865,7 @@
 				D623A5412635FB3C0095BD04 /* PollOptionView.swift in Sources */,
 				D65C6BF525478A9C00A6E89C /* BackgroundableViewController.swift in Sources */,
 				D6AEBB4A23216F0400E5038B /* UnfollowAccountActivity.swift in Sources */,
+				D61DC84D28F500D200B82C6E /* NewProfileViewController.swift in Sources */,
 				D663626421360D2300C9CBA2 /* AvatarStyle.swift in Sources */,
 				D6D3FDE024F41B8400FF50A5 /* ComposeContainerView.swift in Sources */,
 				D693A72A25CF8C1E003A14E2 /* ProfileDirectoryViewController.swift in Sources */,

Tusker/Screens/Profile/NewProfileHeaderCollectionViewCell.swift

@@ -0,0 +1,62 @@
+//
+//  NewProfileHeaderCollectionViewCell.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 10/10/22.
+//  Copyright © 2022 Shadowfacts. All rights reserved.
+//
+
+import UIKit
+
+class NewProfileHeaderCollectionViewCell: UICollectionViewCell {
+    
+    private var state: State = .unloaded
+    
+    override init(frame: CGRect) {
+        super.init(frame: frame)
+        
+        contentView.backgroundColor = .systemBackground
+        isOpaque = true
+        contentView.isOpaque = true
+    }
+    
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+    
+    func addHeader(_ header: ProfileHeaderView) {
+        switch state {
+        case .unloaded, .placeholder(heightConstraint: _):
+            header.translatesAutoresizingMaskIntoConstraints = false
+            contentView.embedSubview(header)
+            self.state = .view(header)
+        case .view(_):
+            fatalError("profile header collection view cell already has view")
+        }
+    }
+    
+    func addConstraint(height: CGFloat) -> ProfileHeaderView? {
+        switch state {
+        case .unloaded:
+            let constraint = contentView.heightAnchor.constraint(equalToConstant: height)
+            constraint.isActive = true
+            state = .placeholder(heightConstraint: constraint)
+            return nil
+        case .placeholder(let heightConstraint):
+            heightConstraint.constant = height
+            return nil
+        case .view(let header):
+            let constraint = contentView.heightAnchor.constraint(equalToConstant: height)
+            constraint.isActive = true
+            state = .placeholder(heightConstraint: constraint)
+            return header
+        }
+    }
+    
+    enum State {
+        case unloaded
+        case placeholder(heightConstraint: NSLayoutConstraint)
+        case view(ProfileHeaderView)
+    }
+    
+}

Tusker/Screens/Profile/NewProfileStatusesViewController.swift

@@ -12,29 +12,54 @@ import Combine
 
 class NewProfileStatusesViewController: UIViewController, TimelineLikeCollectionViewController {
     
-    weak var mastodonController: MastodonController!
+    unowned var owner: NewProfileViewController
-    var accountID: String!
+    var mastodonController: MastodonController { owner.mastodonController }
+    private var accountID: String!
     let kind: Kind
+    var initialHeaderMode: HeaderMode?
+    weak var profileHeaderDelegate: ProfileHeaderViewDelegate?
     
     private(set) var controller: TimelineLikeController<TimelineItem>!
     let confirmLoadMore = PassthroughSubject<Void, Never>()
     private var newer: RequestRange?
     private var older: RequestRange?
+    private var cancellables = Set<AnyCancellable>()
     
     var collectionView: UICollectionView {
         view as! UICollectionView
     }
     private(set) var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
     
-    init(accountID: String?, kind: Kind, mastodonController: MastodonController) {
+//    var headerCell: NewProfileHeaderCollectionViewCell? {
+//        guard let accountID,
+//              isViewLoaded,
+//              let indexPath = dataSource.indexPath(for: .header(accountID)),
+//              let cell = collectionView.cellForItem(at: indexPath) as? NewProfileHeaderCollectionViewCell else {
+//            return nil
+//        }
+//        return cell
+//    }
+    private(set) var headerCell: NewProfileHeaderCollectionViewCell?
+    
+    init(accountID: String?, kind: Kind, owner: NewProfileViewController) {
         self.accountID = accountID
         self.kind = kind
-        self.mastodonController = mastodonController
+        self.owner = owner
         
         super.init(nibName: nil, bundle: nil)
         
         self.controller = TimelineLikeController(delegate: self)
         
+        mastodonController.persistentContainer.accountSubject
+            .receive(on: DispatchQueue.main)
+            .filter { [unowned self] in $0 == self.accountID }
+            .sink { [unowned self] id in
+                var snapshot = dataSource.snapshot()
+                snapshot.reconfigureItems([.header(id)])
+                dataSource.apply(snapshot, animatingDifferences: true)
+            }
+            .store(in: &cancellables)
+        
         // TODO: refresh key command
     }
     
@@ -58,7 +83,6 @@ class NewProfileStatusesViewController: UIViewController, TimelineLikeCollection
         
         registerTimelineLikeCells()
         dataSource = createDataSource()
-        applyInitialSnapshot()
         
         // TODO: refresh control
     }
@@ -69,6 +93,12 @@ class NewProfileStatusesViewController: UIViewController, TimelineLikeCollection
     }
     
     private func createDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
+//        let headerCell = UICollectionView.CellRegistration<NewProfileHeaderCollectionViewCell, String> { [unowned self] cell, indexPath, item in
+//            cell.header.delegate = self.profileHeaderDelegate
+//            cell.header.updateUI(for: item)
+//            cell.header.pagesSegmentedControl.selectedSegmentIndex = self.owner.currentIndex ?? 0
+//        }
+        collectionView.register(NewProfileHeaderCollectionViewCell.self, forCellWithReuseIdentifier: "headerCell")
         let statusCell = UICollectionView.CellRegistration<TimelineStatusCollectionViewCell, (String, StatusState, Bool)> { [unowned self] cell, indexPath, item in
             cell.delegate = self
             cell.showPinned = item.2
@@ -76,6 +106,26 @@ class NewProfileStatusesViewController: UIViewController, TimelineLikeCollection
         }
         return UICollectionViewDiffableDataSource(collectionView: collectionView) { [unowned self] collectionView, indexPath, itemIdentifier in
             switch itemIdentifier {
+            case .header(let id):
+                if let headerCell = self.headerCell {
+                    return headerCell
+                } else {
+                    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "headerCell", for: indexPath) as! NewProfileHeaderCollectionViewCell
+                    switch self.initialHeaderMode {
+                    case nil:
+                        fatalError("missing initialHeaderMode")
+                    case .createView:
+                        let view = ProfileHeaderView.create()
+                        view.delegate = self.profileHeaderDelegate
+                        view.updateUI(for: id)
+                        view.pagesSegmentedControl.selectedSegmentIndex = self.owner.currentIndex ?? 0
+                        cell.addHeader(view)
+                    case .placeholder(height: let height):
+                        _ = cell.addConstraint(height: height)
+                    }
+                    self.headerCell = cell
+                    return cell
+                }
             case .status(id: let id, state: let state, pinned: let pinned):
                 return collectionView.dequeueConfiguredReusableCell(using: statusCell, for: indexPath, item: (id, state, pinned))
             case .loadingIndicator:
@@ -86,10 +136,6 @@ class NewProfileStatusesViewController: UIViewController, TimelineLikeCollection
         }
     }
     
-    private func applyInitialSnapshot() {
-        // TODO: header
-    }
-    
     override func viewWillAppear(_ animated: Bool) {
         super.viewWillAppear(animated)
         
@@ -98,8 +144,7 @@ class NewProfileStatusesViewController: UIViewController, TimelineLikeCollection
         }
         
         Task {
-            await controller.loadInitial()
+            await load()
-            await tryLoadPinned()
         }
     }
     
@@ -111,16 +156,38 @@ class NewProfileStatusesViewController: UIViewController, TimelineLikeCollection
     
     // TODO: refreshing
     
+    func setAccountID(_ id: String) {
+        self.accountID = id
+        // TODO: maybe this function should be async?
+        Task {
+            await load()
+        }
+    }
+    
+    private func load() async {
+        guard accountID != nil,
+              await controller.state == .notLoadedInitial else {
+            return
+        }
+        
+        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
+        snapshot.appendSections([.header, .pinned, .statuses])
+        snapshot.appendItems([.header(accountID)], toSection: .header)
+        await apply(snapshot, animatingDifferences: false)
+        print("added header item")
+        
+        await controller.loadInitial()
+        await tryLoadPinned()
+    }
+    
     private func tryLoadPinned() async {
         do {
             try await loadPinned()
         } catch {
             let config = ToastConfiguration(from: error, with: "Loading Pinned", in: self) { toast in
                 toast.dismissToast(animated: true)
-                Task {
                 await self.tryLoadPinned()
             }
-            }
             self.showToast(configuration: config, animated: true)
         }
     }
@@ -141,13 +208,6 @@ class NewProfileStatusesViewController: UIViewController, TimelineLikeCollection
         }
         
         var snapshot = dataSource.snapshot()
-        if !snapshot.sectionIdentifiers.contains(.pinned) {
-            if snapshot.sectionIdentifiers.isEmpty {
-                snapshot.appendSections([.pinned])
-            } else {
-                snapshot.insertSections([.pinned], beforeSection: snapshot.sectionIdentifiers.first!)
-            }
-        }
         let items = statuses.map { Item.status(id: $0.id, state: .unknown, pinned: true) }
         snapshot.appendItems(items, toSection: .pinned)
         await apply(snapshot, animatingDifferences: true)
@@ -159,10 +219,14 @@ extension NewProfileStatusesViewController {
     enum Kind {
         case statuses, withReplies, onlyMedia
     }
+    enum HeaderMode {
+        case createView, placeholder(height: CGFloat)
+    }
 }
 
 extension NewProfileStatusesViewController {
     enum Section: TimelineLikeCollectionViewSection {
+        case header
         case pinned
         case statuses
         case footer
@@ -172,6 +236,7 @@ extension NewProfileStatusesViewController {
     enum Item: TimelineLikeCollectionViewItem {
         typealias TimelineItem = String
         
+        case header(String)
         case status(id: String, state: StatusState, pinned: Bool)
         case loadingIndicator
         case confirmLoadMore
@@ -182,6 +247,8 @@ extension NewProfileStatusesViewController {
         
         static func ==(lhs: Item, rhs: Item) -> Bool {
             switch (lhs, rhs) {
+            case let (.header(a), .header(b)):
+                return a == b
             case let (.status(id: a, state: _, pinned: ap), .status(id: b, state: _, pinned: bp)):
                 return a == b && ap == bp
             case (.loadingIndicator, .loadingIndicator):
@@ -195,14 +262,17 @@ extension NewProfileStatusesViewController {
         
         func hash(into hasher: inout Hasher) {
             switch self {
-            case .status(id: let id, state: _, pinned: let pinned):
+            case .header(let id):
                 hasher.combine(0)
                 hasher.combine(id)
+            case .status(id: let id, state: _, pinned: let pinned):
+                hasher.combine(1)
+                hasher.combine(id)
                 hasher.combine(pinned)
             case .loadingIndicator:
-                hasher.combine(1)
-            case .confirmLoadMore:
                 hasher.combine(2)
+            case .confirmLoadMore:
+                hasher.combine(3)
             }
         }
     }
@@ -223,10 +293,6 @@ extension NewProfileStatusesViewController: TimelineLikeControllerDelegate {
     }
     
     func loadInitial() async throws -> [String] {
-        guard let mastodonController else {
-            throw Error.noClient
-        }
-        
         let request = request()
         let (statuses, _) = try await mastodonController.run(request)
         
@@ -285,7 +351,6 @@ extension NewProfileStatusesViewController: TimelineLikeControllerDelegate {
     }
     
     enum Error: TimelineLikeCollectionViewError {
-        case noClient
         case noNewer
         case noOlder
         case allCaughtUp

Tusker/Screens/Profile/NewProfileViewController.swift

@@ -0,0 +1,245 @@
+//
+//  NewProfileViewController.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 10/10/22.
+//  Copyright © 2022 Shadowfacts. All rights reserved.
+//
+
+import UIKit
+import Pachyderm
+
+class NewProfileViewController: UIPageViewController {
+    
+    weak var mastodonController: MastodonController!
+    
+    // This property is optional because MyProfileViewController may not have the user's account ID
+    // when first constructed. It should never be set to nil.
+    var accountID: String? {
+        willSet {
+            precondition(newValue != nil, "Do not set ProfileViewController.accountID to nil")
+        }
+        didSet {
+            pageControllers.forEach { $0.setAccountID(accountID!) }
+            Task {
+                await loadAccount()
+            }
+        }
+    }
+
+    private(set) var currentIndex: Int!
+    private var pageControllers: [NewProfileStatusesViewController]!
+    var currentViewController: NewProfileStatusesViewController {
+        pageControllers[currentIndex]
+    }
+    
+    private var state: State = .idle
+    
+    init(accountID: String?, mastodonController: MastodonController) {
+        self.accountID = accountID
+        self.mastodonController = mastodonController
+        
+        super.init(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
+        
+        self.pageControllers = [
+            .init(accountID: accountID, kind: .statuses, owner: self),
+            .init(accountID: accountID, kind: .withReplies, owner: self),
+            .init(accountID: accountID, kind: .onlyMedia, owner: self),
+        ]
+    }
+    
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+    
+    override func viewDidLoad() {
+        super.viewDidLoad()
+
+        view.backgroundColor = .systemBackground
+        
+        for pageController in pageControllers {
+            pageController.profileHeaderDelegate = self
+        }
+        
+        selectPage(at: 0, animated: false)
+        
+        // TODO: compose button
+        
+        // TODO: key commands
+        
+        Task {
+            await loadAccount()
+        }
+        
+        // TODO: configure nav controller appearance
+    }
+    
+    private func loadAccount() async {
+        guard let accountID else {
+            return
+        }
+        if let account = mastodonController.persistentContainer.account(for: accountID) {
+            updateAccountUI(account: account)
+        } else {
+            do {
+                let req = Client.getAccount(id: accountID)
+                let (account, _) = try await mastodonController.run(req)
+                let mo = await withCheckedContinuation { continuation in
+                    mastodonController.persistentContainer.addOrUpdate(account: account) { (mo) in
+                        continuation.resume(returning: mo)
+                    }
+                }
+                self.updateAccountUI(account: mo)
+            } catch {
+                let config = ToastConfiguration(from: error, with: "Loading Account", in: self) { [unowned self] toast in
+                    toast.dismissToast(animated: true)
+                    await self.loadAccount()
+                }
+                self.showToast(configuration: config, animated: true)
+            }
+        }
+    }
+    
+    private func updateAccountUI(account: AccountMO) {
+        if let currentAccountID = mastodonController.accountInfo?.id {
+            userActivity = UserActivityManager.showProfileActivity(id: account.id, accountID: currentAccountID)
+        }
+        
+        navigationItem.title = account.displayNameWithoutCustomEmoji
+    }
+    
+    private func selectPage(at index: Int, animated: Bool, completion: ((Bool) -> Void)? = nil) {
+        guard case .idle = state else {
+            return
+        }
+        
+        state = .animating
+        
+        let direction: UIPageViewController.NavigationDirection
+        if currentIndex == nil || index - currentIndex > 0 {
+            direction = .forward
+        } else {
+            direction = .reverse
+        }
+        
+        guard let old = viewControllers?.first as? NewProfileStatusesViewController else {
+            // if old doesn't exist, we're selecting the initial view controller, so moving the header around isn't necessary
+            pageControllers[index].initialHeaderMode = .createView
+            setViewControllers([pageControllers[index]], direction: direction, animated: animated) { finished in
+                self.state = .idle
+                completion?(finished)
+            }
+            currentIndex = index
+            return
+        }
+        let new = pageControllers[index]
+        
+        currentIndex = index
+        
+        // TODO: old.headerCell could be nil if scrolled down and key command used
+        let oldHeaderCell = old.headerCell!
+        
+        // old header cell must have the header view
+        let headerView = oldHeaderCell.addConstraint(height: oldHeaderCell.bounds.height)!
+        
+        if new.isViewLoaded {
+            _ = new.headerCell!.addConstraint(height: oldHeaderCell.bounds.height)
+        } else {
+            new.initialHeaderMode = .placeholder(height: oldHeaderCell.bounds.height)
+        }
+        
+        // disable user interaction during animation, to avoid any potential weird race conditions
+        headerView.isUserInteractionEnabled = false
+        headerView.layer.zPosition = 100
+        view.addSubview(headerView)
+        let oldHeaderCellTop = oldHeaderCell.convert(CGPoint.zero, to: view).y
+        // TODO: use safe area layout guide instead of manually adjusting this?
+        let headerTopOffset = oldHeaderCellTop - view.safeAreaInsets.top
+        NSLayoutConstraint.activate([
+            headerView.topAnchor.constraint(equalTo: view.topAnchor, constant: headerTopOffset),
+            headerView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
+            headerView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
+        ])
+        
+        // hide scroll indicators during the transition because otherwise the show through the
+        // profile header, even though it has an opaque background
+        old.collectionView.showsVerticalScrollIndicator = false
+        if new.isViewLoaded {
+            new.collectionView.showsVerticalScrollIndicator = false
+        }
+        
+        // if the new view isn't loaded or it isn't tall enough to match content offsets, animate scrolling old back to top to match new
+        if animated,
+           !new.isViewLoaded || new.collectionView.contentSize.height - new.collectionView.bounds.height < old.collectionView.contentOffset.y {
+            // We need to display a snapshot over the old view because setting the content offset to the top w/o animating
+            // results in the collection view immediately removing cells that will be offscreen.
+            // And we can't just call setContentOffset(_:animated:) because its animation curve does not match ours/the page views
+            // So, we capture a snapshot before the content offset is changed, so those cells can be shown during the animation,
+            // rather than a gap appearing during it.
+            let snapshot = old.collectionView.snapshotView(afterScreenUpdates: true)!
+            let origOldContentOffset = old.collectionView.contentOffset
+            old.collectionView.contentOffset = CGPoint(x: 0, y: view.safeAreaInsets.top)
+            
+            snapshot.frame = old.collectionView.bounds
+            snapshot.frame.origin.y = 0
+            snapshot.layer.zPosition = 99
+            view.addSubview(snapshot)
+            
+            // empirically, 0.3s seems to match the UIPageViewController animation
+            UIView.animate(withDuration: 0.3, delay: 0, options: .curveEaseInOut) {
+                // animate the snapshot offscreen in the same direction as the old view
+                snapshot.frame.origin.x = direction == .forward ? -self.view.bounds.width : self.view.bounds.width
+                // animate the snapshot to be "scrolled" to top
+                snapshot.frame.origin.y = self.view.safeAreaInsets.top + origOldContentOffset.y
+                // if scrolling because the new collection view's content isn't tall enough, make sure to scroll it to top as well
+                if new.isViewLoaded {
+                    new.collectionView.contentOffset = CGPoint(x: 0, y: -self.view.safeAreaInsets.top)
+                }
+                headerView.transform = CGAffineTransform(translationX: 0, y: -headerTopOffset)
+            } completion: { _ in
+                snapshot.removeFromSuperview()
+            }
+        } else if new.isViewLoaded {
+            new.collectionView.contentOffset = old.collectionView.contentOffset
+        }
+        
+        setViewControllers([pageControllers[index]], direction: direction, animated: animated) { finished in
+            // reenable scroll indicators after the switching animation is done
+            old.collectionView.showsVerticalScrollIndicator = true
+            new.collectionView.showsVerticalScrollIndicator = true
+            
+            headerView.isUserInteractionEnabled = true
+            
+            headerView.transform = .identity
+            headerView.layer.zPosition = 0
+            // move the header view into the new page controller's cell
+            // new's headerCell should always be non-nil, because the account must be loaded (in order to have triggered this switch), and so new should add the cell immediately on load
+            new.headerCell!.addHeader(headerView)
+            
+            self.state = .idle
+            completion?(finished)
+        }
+    }
+    
+    enum State {
+        case idle
+        case animating
+    }
+
+}
+
+extension NewProfileViewController: TuskerNavigationDelegate {
+    var apiController: MastodonController { mastodonController }
+}
+
+extension NewProfileViewController: ToastableViewController {
+}
+
+extension NewProfileViewController: ProfileHeaderViewDelegate {
+    func profileHeader(_ headerView: ProfileHeaderView, selectedPostsIndexChangedTo newIndex: Int) {
+        guard case .idle = state else {
+            return
+        }
+        selectPage(at: newIndex, animated: true)
+    }
+}

Tusker/Screens/Utilities/SplitNavigationController.swift

@@ -271,7 +271,8 @@ private class SplitSecondaryNavigationController: EnhancedNavigationViewControll
     override var next: UIResponder? {
         // ordinarily, the next responder in the chain would be the SplitNavigationController's view
         // but that would bypass the VC in the root nav, so we reroute the repsonder chain to include it
-        owner.viewControllers.first!.view
+        // first seems to be nil when using the view debugger for some reason, so in that case, defer to super
+        owner.viewControllers.first?.view ?? super.next
     }
     
     private func configureSecondarySplitCloseButton(for viewController: UIViewController) {

Tusker/TuskerNavigationDelegate.swift

@@ -34,7 +34,7 @@ extension TuskerNavigationDelegate {
         }
         
 //        show(ProfileViewController(accountID: accountID, mastodonController: apiController), sender: self)
-        show(NewProfileStatusesViewController(accountID: accountID, kind: .statuses, mastodonController: apiController), sender: self)
+        show(NewProfileViewController(accountID: accountID, mastodonController: apiController), sender: self)
     }
     
     func selected(mention: Mention) {