Show threads on Conversation screen

Tusker.xcodeproj/project.pbxproj

@@ -272,6 +272,8 @@
 		D6C693FC2162FE6F007D6A6D /* LoadingViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C693FB2162FE6F007D6A6D /* LoadingViewController.swift */; };
 		D6C693FE2162FEEA007D6A6D /* UIViewController+Children.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C693FD2162FEEA007D6A6D /* UIViewController+Children.swift */; };
 		D6C7D27D22B6EBF800071952 /* AttachmentsContainerView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C7D27C22B6EBF800071952 /* AttachmentsContainerView.swift */; };
+		D6C82B5625C5F3F20017F1E6 /* ExpandThreadTableViewCell.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C82B5425C5F3F20017F1E6 /* ExpandThreadTableViewCell.swift */; };
+		D6C82B5725C5F3F20017F1E6 /* ExpandThreadTableViewCell.xib in Resources */ = {isa = PBXBuildFile; fileRef = D6C82B5525C5F3F20017F1E6 /* ExpandThreadTableViewCell.xib */; };
 		D6C94D872139E62700CB5196 /* LargeImageViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C94D862139E62700CB5196 /* LargeImageViewController.swift */; };
 		D6C94D892139E6EC00CB5196 /* AttachmentView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C94D882139E6EC00CB5196 /* AttachmentView.swift */; };
 		D6C99FC724FACFAB005C74D3 /* ActivityIndicatorView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C99FC624FACFAB005C74D3 /* ActivityIndicatorView.swift */; };
@@ -634,6 +636,8 @@
 		D6C693FB2162FE6F007D6A6D /* LoadingViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LoadingViewController.swift; sourceTree = "<group>"; };
 		D6C693FD2162FEEA007D6A6D /* UIViewController+Children.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "UIViewController+Children.swift"; sourceTree = "<group>"; };
 		D6C7D27C22B6EBF800071952 /* AttachmentsContainerView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AttachmentsContainerView.swift; sourceTree = "<group>"; };
+		D6C82B5425C5F3F20017F1E6 /* ExpandThreadTableViewCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ExpandThreadTableViewCell.swift; sourceTree = "<group>"; };
+		D6C82B5525C5F3F20017F1E6 /* ExpandThreadTableViewCell.xib */ = {isa = PBXFileReference; lastKnownFileType = file.xib; path = ExpandThreadTableViewCell.xib; sourceTree = "<group>"; };
 		D6C94D862139E62700CB5196 /* LargeImageViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LargeImageViewController.swift; sourceTree = "<group>"; };
 		D6C94D882139E6EC00CB5196 /* AttachmentView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AttachmentView.swift; sourceTree = "<group>"; };
 		D6C99FC624FACFAB005C74D3 /* ActivityIndicatorView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ActivityIndicatorView.swift; sourceTree = "<group>"; };
@@ -1043,6 +1047,8 @@
 			isa = PBXGroup;
 			children = (
 				D667E5F42135BCD50057A976 /* ConversationTableViewController.swift */,
+				D6C82B5425C5F3F20017F1E6 /* ExpandThreadTableViewCell.swift */,
+				D6C82B5525C5F3F20017F1E6 /* ExpandThreadTableViewCell.xib */,
 			);
 			path = Conversation;
 			sourceTree = "<group>";
@@ -1746,6 +1752,7 @@
 				D627FF7D217E958900CC0648 /* DraftTableViewCell.xib in Resources */,
 				D6A3BC7D232195C600FD64D5 /* ActionNotificationGroupTableViewCell.xib in Resources */,
 				D6412B0B24B0D4C600F5412E /* ProfileHeaderView.xib in Resources */,
+				D6C82B5725C5F3F20017F1E6 /* ExpandThreadTableViewCell.xib in Resources */,
 				D6D4DDDA212518A200E1C4BB /* LaunchScreen.storyboard in Resources */,
 				D6E57FA325C26FAB00341037 /* Localizable.stringsdict in Resources */,
 				D6B053AC23BD2F1400A066FA /* AssetCollectionViewCell.xib in Resources */,
@@ -2013,6 +2020,7 @@
 				D626493823C0FD0000612E6E /* AllPhotosTableViewCell.swift in Sources */,
 				D627943B23A55BA600D38C68 /* NavigableTableViewCell.swift in Sources */,
 				D6333B792139AEFD00CE884A /* Date+TimeAgo.swift in Sources */,
+				D6C82B5625C5F3F20017F1E6 /* ExpandThreadTableViewCell.swift in Sources */,
 				D686BBE324FBF8110068E6AA /* WrappedProgressView.swift in Sources */,
 				D620483423D3801D008A63EF /* LinkTextView.swift in Sources */,
 				D6412B0D24B0D4CF00F5412E /* ProfileHeaderView.swift in Sources */,

Tusker/Screens/Conversation/ConversationTableViewController.swift

@@ -8,23 +8,30 @@
 
 import UIKit
 import Pachyderm
+import CoreData
+
+class ConversationNode {
+    let status: StatusMO
+    var children: [ConversationNode]
+    
+    init(status: StatusMO) {
+        self.status = status
+        self.children = []
+    }
+}
 
 class ConversationTableViewController: EnhancedTableViewController {
     
     static let showPostsImage = UIImage(systemName: "eye.fill")!
     static let hidePostsImage = UIImage(systemName: "eye.slash.fill")!
     
+    static let bottomSeparatorTag = 101
+    
     weak var mastodonController: MastodonController!
     
     let mainStatusID: String
     let mainStatusState: StatusState
-    var statuses: [(id: String, state: StatusState)] = [] {
+    private(set) var dataSource: UITableViewDiffableDataSource<Section, Item>!
-        didSet {
-            DispatchQueue.main.async {
-                self.tableView.reloadData()
-            }
-        }
-    }
     
     var showStatusesAutomatically = false
     var visibilityBarButtonItem: UIBarButtonItem!
@@ -45,7 +52,8 @@ class ConversationTableViewController: EnhancedTableViewController {
     
     deinit {
         guard let persistentContainer = mastodonController?.persistentContainer else { return }
-        for (id, _) in statuses {
+        let snapshot = dataSource.snapshot()
+        for case let .status(id: id, state: _) in snapshot.itemIdentifiers {
             persistentContainer.status(for: id)?.decrementReferenceCount()
         }
     }
@@ -60,13 +68,72 @@ class ConversationTableViewController: EnhancedTableViewController {
         
         tableView.register(UINib(nibName: "TimelineStatusTableViewCell", bundle: nil), forCellReuseIdentifier: "statusCell")
         tableView.register(UINib(nibName: "ConversationMainStatusTableViewCell", bundle: nil), forCellReuseIdentifier: "mainStatusCell")
+        tableView.register(UINib(nibName: "ExpandThreadTableViewCell", bundle: .main), forCellReuseIdentifier: "expandThreadCell")
         
         tableView.prefetchDataSource = self
         
-        visibilityBarButtonItem = UIBarButtonItem(image: ConversationTableViewController.showPostsImage, style: .plain, target: self, action: #selector(toggleVisibilityButtonPressed))
+        tableView.backgroundColor = .secondarySystemBackground
+        // separators are disabled on the table view so we can re-add them ourselves
+        // so they're not inserted in between statuses in the ame sub-thread
+        tableView.separatorStyle = .none
+        
+        dataSource = UITableViewDiffableDataSource<Section, Item>(tableView: tableView, cellProvider: { (tableView, indexPath, item) -> UITableViewCell? in
+            switch item {
+            case let .status(id: id, state: state):
+                let rowsInSection = self.dataSource.tableView(tableView, numberOfRowsInSection: indexPath.section)
+                let firstInSection = indexPath.row == 0
+                let lastInSection = indexPath.row == rowsInSection - 1
+                
+                let identifier = id == self.mainStatusID ? "mainStatusCell" : "statusCell"
+                let cell = tableView.dequeueReusableCell(withIdentifier: identifier, for: indexPath) as! BaseStatusTableViewCell
+                
+                cell.delegate = self
+                cell.showStatusAutomatically = self.showStatusesAutomatically
+                
+                if let cell = cell as? TimelineStatusTableViewCell {
+                    cell.showReplyIndicator = false
+                }
+                
+                cell.updateUI(statusID: id, state: state)
+                
+                cell.setShowThreadLinks(prev: !firstInSection, next: !lastInSection)
+                if lastInSection {
+                    if cell.viewWithTag(ConversationTableViewController.bottomSeparatorTag) == nil {
+                        let separator = UIView()
+                        separator.tag = ConversationTableViewController.bottomSeparatorTag
+                        separator.translatesAutoresizingMaskIntoConstraints = false
+                        separator.backgroundColor = tableView.separatorColor
+                        cell.addSubview(separator)
+                        NSLayoutConstraint.activate([
+                            separator.heightAnchor.constraint(equalToConstant: 0.5),
+                            separator.bottomAnchor.constraint(equalTo: cell.bottomAnchor),
+                            separator.leftAnchor.constraint(equalTo: cell.leftAnchor, constant: cell.separatorInset.left),
+                            separator.rightAnchor.constraint(equalTo: cell.rightAnchor),
+                        ])
+                    }
+                } else {
+                    cell.viewWithTag(ConversationTableViewController.bottomSeparatorTag)?.removeFromSuperview()
+                }
+                
+                return cell
+                
+            case let .expandThread(childThreads: childThreads):
+                let cell = tableView.dequeueReusableCell(withIdentifier: "expandThreadCell", for: indexPath) as! ExpandThreadTableViewCell
+                cell.updateUI(childThreads: childThreads)
+                return cell
+            }
+        })
+        
+        let initialImage = showStatusesAutomatically ? ConversationTableViewController.hidePostsImage : ConversationTableViewController.showPostsImage
+        visibilityBarButtonItem = UIBarButtonItem(image: initialImage, style: .plain, target: self, action: #selector(toggleVisibilityButtonPressed))
         navigationItem.rightBarButtonItem = visibilityBarButtonItem
 
-        statuses = [(mainStatusID, mainStatusState)]
+        let mainStatusItem = Item.status(id: mainStatusID, state: mainStatusState)
+        
+        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
+        snapshot.appendSections([.statuses])
+        snapshot.appendItems([mainStatusItem], toSection: .statuses)
+        dataSource.apply(snapshot, animatingDifferences: false)
 
         guard let mainStatus = self.mastodonController.persistentContainer.status(for: self.mainStatusID) else {
             fatalError("Missing cached status \(self.mainStatusID)")
@@ -80,19 +147,39 @@ class ConversationTableViewController: EnhancedTableViewController {
 
             let parents = self.getDirectParents(inReplyTo: mainStatusInReplyToID, from: context.ancestors)
             let parentStatuses = context.ancestors.filter { parents.contains($0.id) }
-            self.mastodonController.persistentContainer.addAll(statuses: parentStatuses) {
+            
-                self.mastodonController.persistentContainer.addAll(statuses: context.descendants) {
+            // todo: should this really be blindly adding all the descendants?
-                    self.statuses = parents.map { ($0, .unknown) } + self.statuses + context.descendants.map { ($0.id, .unknown) }
+            self.mastodonController.persistentContainer.addAll(statuses: parentStatuses + context.descendants) {
-                    let indexPath = IndexPath(row: parents.count, section: 0)
+                DispatchQueue.main.async {
-                    DispatchQueue.main.async {
+                    var snapshot = self.dataSource.snapshot()
-                        self.tableView.scrollToRow(at: indexPath, at: .middle, animated: false)
+                    snapshot.insertItems(parents.map { .status(id: $0, state: .unknown) }, beforeItem: mainStatusItem)
+                    
+                    // fetch all descendant status managed objects
+                    let descendantIDs = context.descendants.map(\.id)
+                    let request: NSFetchRequest<StatusMO> = StatusMO.fetchRequest()
+                    request.predicate = NSPredicate(format: "id in %@", descendantIDs)
+                    
+                    if let descendants = try? self.mastodonController.persistentContainer.viewContext.fetch(request) {
+                        // convert array of descendant statuses into tree of sub-threads
+                        let childThreads = self.getDescendantThreads(mainStatus: mainStatus, descendants: descendants)
+                        
+                        // convert sub-threads into items for section and add to snapshot
+                        self.addFlattenedChildThreadsToSnapshot(childThreads, mainStatus: mainStatus, snapshot: &snapshot)
+                    }
+                    
+                    self.dataSource.apply(snapshot, animatingDifferences: false) {
+                        // ensure that the main status is on-screen after newly loaded statuses are added
+                        // todo: should this not happen if the user has already started scrolling (e.g. because the main status is very long)?
+                        if let indexPath = self.dataSource.indexPath(for: mainStatusItem) {
+                            self.tableView.scrollToRow(at: indexPath, at: .middle, animated: false)
+                        }
                     }
                 }
             }
         }
     }
 
-    func getDirectParents(inReplyTo inReplyToID: String?, from statuses: [Status]) -> [String] {
+    private func getDirectParents(inReplyTo inReplyToID: String?, from statuses: [Status]) -> [String] {
         var statuses = statuses
         var parents = [String]()
         
@@ -107,38 +194,99 @@ class ConversationTableViewController: EnhancedTableViewController {
         return parents
     }
     
-    // MARK: - Table view data source
+    private func getDescendantThreads(mainStatus: StatusMO, descendants: [StatusMO]) -> [ConversationNode] {
+        var descendants = descendants
         
-    override func numberOfSections(in tableView: UITableView) -> Int {
+        func removeAllInReplyTo(id: String) -> [StatusMO] {
-        return 1
+            let statuses = descendants.filter { $0.inReplyToID == id }
+            descendants.removeAll { $0.inReplyToID == id }
+            return statuses
+        }
+        
+        var nodes: [String: ConversationNode] = [
+            mainStatus.id: ConversationNode(status: mainStatus)
+        ]
+        
+        var idsToCheck = [mainStatusID]
+        
+        while !idsToCheck.isEmpty {
+            let inReplyToID = idsToCheck.removeFirst()
+            let nodeForID = nodes[inReplyToID]!
+            
+            let inReply = removeAllInReplyTo(id: inReplyToID)
+            for reply in inReply {
+                idsToCheck.append(reply.id)
+                
+                let replyNode = ConversationNode(status: reply)
+                nodes[reply.id] = replyNode
+                
+                nodeForID.children.append(replyNode)
+            }
+        }
+        
+        return nodes[mainStatusID]!.children
     }
     
-    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
+    private func addFlattenedChildThreadsToSnapshot(_ childThreads: [ConversationNode], mainStatus: StatusMO, snapshot: inout NSDiffableDataSourceSnapshot<Section, Item>) {
-        return statuses.count
+        var childThreads = childThreads
+        
+        // child threads by the same author as the main status come first
+        let pivotIndex = childThreads.partition(by: { $0.status.account.id != mainStatus.account.id })
+        
+        // within each group, child threads are sorted chronologically
+        childThreads[0..<pivotIndex].sort(by: { $0.status.createdAt < $1.status.createdAt })
+        childThreads[pivotIndex...].sort(by: { $0.status.createdAt < $1.status.createdAt })
+        
+        for node in childThreads {
+            snapshot.appendSections([.childThread(firstStatusID: node.status.id)])
+            snapshot.appendItems([.status(id: node.status.id, state: .unknown)])
+            
+            var currentNode = node
+            while true {
+                let next: ConversationNode
+                
+                if currentNode.children.count == 0 {
+                    break
+                } else if currentNode.children.count == 1 {
+                    next = currentNode.children[0]
+                } else {
+                    let sameAuthorStatuses = currentNode.children.filter({ $0.status.account.id == node.status.account.id })
+                    if sameAuthorStatuses.count == 1 {
+                        next = sameAuthorStatuses[0]
+                    } else {
+                        snapshot.appendItems([.expandThread(childThreads: currentNode.children)])
+                        break
+                    }
+                }
+                
+                currentNode = next
+                snapshot.appendItems([.status(id: next.status.id, state: .unknown)])
+            }
+        }
     }
     
-    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
+    func item(for indexPath: IndexPath) -> (id: String, state: StatusState)? {
-        let (id, state) = statuses[indexPath.row]
+        return self.dataSource.itemIdentifier(for: indexPath).flatMap { (item) in
-        
+            switch item {
-        if id == mainStatusID {
+            case let .status(id: id, state: state):
-            guard let cell = tableView.dequeueReusableCell(withIdentifier: "mainStatusCell", for: indexPath) as? ConversationMainStatusTableViewCell else { fatalError() }
+                return (id: id, state: state)
-            cell.selectionStyle = .none
+            default:
-            cell.showStatusAutomatically = showStatusesAutomatically
+                return nil
-            cell.delegate = self
+            }
-            cell.updateUI(statusID: id, state: state)
-            return cell
-        } else {
-            guard let cell = tableView.dequeueReusableCell(withIdentifier: "statusCell", for: indexPath) as? TimelineStatusTableViewCell else { fatalError() }
-            cell.showStatusAutomatically = showStatusesAutomatically
-            cell.showReplyIndicator = false
-            cell.delegate = self
-            cell.updateUI(statusID: id, state: state)
-            return cell
         }
     }
     
     // MARK: - Table view delegate
     
+    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
+        if case .expandThread = dataSource.itemIdentifier(for: indexPath),
+           case let .status(id: id, state: state) = dataSource.itemIdentifier(for: IndexPath(row: indexPath.row - 1, section: indexPath.section)) {
+            self.selected(status: id, state: state)
+        } else {
+            super.tableView(tableView, didSelectRowAt: indexPath)
+        }
+    }
+    
     override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
         return true
     }
@@ -154,7 +302,8 @@ class ConversationTableViewController: EnhancedTableViewController {
     @objc func toggleVisibilityButtonPressed() {
         showStatusesAutomatically = !showStatusesAutomatically
         
-        for (_, state) in statuses where state.collapsible == true {
+        let snapshot = dataSource.snapshot()
+        for case let .status(id: _, state: state) in snapshot.itemIdentifiers where state.collapsible == true {
             state.collapsed = !showStatusesAutomatically
         }
         
@@ -178,6 +327,48 @@ class ConversationTableViewController: EnhancedTableViewController {
 
 }
 
+extension ConversationTableViewController {
+    enum Section: Hashable {
+        case statuses
+        case childThread(firstStatusID: String)
+    }
+    enum Item: Hashable {
+        case status(id: String, state: StatusState)
+        case expandThread(childThreads: [ConversationNode])
+        
+        static func == (lhs: Item, rhs: Item) -> Bool {
+            switch (lhs, rhs) {
+            case let (.status(id: a, state: _), .status(id: b, state: _)):
+                return a == b
+            case let (.expandThread(childThreads: a), .expandThread(childThreads: b)):
+                return zip(a, b).allSatisfy { $0.status.id == $1.status.id }
+            default:
+                return false
+            }
+        }
+        
+        func hash(into hasher: inout Hasher) {
+            switch self {
+            case let .status(id: id, state: _):
+                hasher.combine("status")
+                hasher.combine(id)
+            case let .expandThread(childThreads: children):
+                hasher.combine("expandThread")
+                hasher.combine(children.map(\.status.id))
+            }
+        }
+    }
+}
+
+extension ConversationTableViewController: TuskerNavigationDelegate {
+    func conversation(mainStatusID: String, state: StatusState) -> ConversationTableViewController {
+        let vc = ConversationTableViewController(for: mainStatusID, state: state, mastodonController: mastodonController)
+        // transfer show statuses automatically state when showing new conversation
+        vc.showStatusesAutomatically = self.showStatusesAutomatically
+        return vc
+    }
+}
+
 extension ConversationTableViewController: StatusTableViewCellDelegate {
     var apiController: MastodonController { mastodonController }
     func statusCellCollapsedStateChanged(_ cell: BaseStatusTableViewCell) {
@@ -189,12 +380,12 @@ extension ConversationTableViewController: StatusTableViewCellDelegate {
 
 extension ConversationTableViewController: UITableViewDataSourcePrefetching, StatusTablePrefetching {
     func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
-        let ids = indexPaths.map { statuses[$0.row].id }
+        let ids: [String] = indexPaths.compactMap { item(for: $0)?.id }
         prefetchStatuses(with: ids)
     }
     
     func tableView(_ tableView: UITableView, cancelPrefetchingForRowsAt indexPaths: [IndexPath]) {
-        let ids: [String] = indexPaths.compactMap { statuses[$0.row].id }
+        let ids: [String] = indexPaths.compactMap { item(for: $0)?.id }
         cancelPrefetchingStatuses(with: ids)
     }
 }

Tusker/Screens/Conversation/ExpandThreadTableViewCell.swift

@@ -0,0 +1,112 @@
+//
+//  ExpandThreadTableViewCell.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 1/30/21.
+//  Copyright © 2021 Shadowfacts. All rights reserved.
+//
+
+import UIKit
+
+class ExpandThreadTableViewCell: UITableViewCell {
+
+    @IBOutlet weak var avatarContainerView: UIView!
+    @IBOutlet weak var avatarContainerWidthConstraint: NSLayoutConstraint!
+    @IBOutlet weak var replyCountLabel: UILabel!
+    var avatarImageViews: [UIImageView] = []
+    
+    private var avatarRequests: [ImageCache.Request] = []
+    
+    override func awakeFromNib() {
+        super.awakeFromNib()
+        
+        let prevThreadLinkView = UIView()
+        prevThreadLinkView.translatesAutoresizingMaskIntoConstraints = false
+        prevThreadLinkView.backgroundColor = tintColor.withAlphaComponent(0.5)
+        prevThreadLinkView.layer.cornerRadius = 2.5
+        prevThreadLinkView.layer.maskedCorners = [.layerMinXMaxYCorner, .layerMaxXMaxYCorner]
+        contentView.addSubview(prevThreadLinkView)
+        NSLayoutConstraint.activate([
+            prevThreadLinkView.widthAnchor.constraint(equalToConstant: 5),
+            prevThreadLinkView.centerXAnchor.constraint(equalTo: leadingAnchor, constant: 16 + 25),
+            prevThreadLinkView.topAnchor.constraint(equalTo: topAnchor),
+            prevThreadLinkView.bottomAnchor.constraint(equalTo: avatarContainerView.topAnchor, constant: -2),
+        ])
+        
+        NotificationCenter.default.addObserver(self, selector: #selector(preferencesChanged), name: .preferencesChanged, object: nil)
+    }
+    
+    func updateUI(childThreads: [ConversationNode]) {
+        let format = NSLocalizedString("expand threads count", comment: "expand conversation threads button label")
+        replyCountLabel.text = String.localizedStringWithFormat(format, childThreads.count)
+        
+        let accounts = childThreads.map(\.status.account).uniques().prefix(3)
+        
+        avatarImageViews.forEach { $0.removeFromSuperview() }
+        avatarImageViews = []
+        
+        avatarRequests = []
+        
+        let avatarImageSize: CGFloat = 44 - 12
+        
+        if accounts.count == 1 {
+            avatarContainerWidthConstraint.constant = avatarImageSize
+        } else {
+            avatarContainerWidthConstraint.constant = CGFloat(accounts.count) * avatarImageSize * 3 / 4
+        }
+        
+        for (index, account) in accounts.enumerated() {
+            let accountImageView = UIImageView()
+            accountImageView.translatesAutoresizingMaskIntoConstraints = false
+            accountImageView.contentMode = .scaleAspectFit
+            accountImageView.layer.cornerRadius = Preferences.shared.avatarStyle.cornerRadiusFraction * avatarImageSize
+            accountImageView.layer.masksToBounds = true
+            accountImageView.layer.borderWidth = 1
+            accountImageView.layer.borderColor = UIColor.secondarySystemBackground.cgColor
+            // need a solid background color so semi-transparent avatars don't look bad
+            accountImageView.backgroundColor = .secondarySystemBackground
+            avatarContainerView.addSubview(accountImageView)
+            
+            avatarImageViews.append(accountImageView)
+                
+            accountImageView.layer.zPosition = CGFloat(-index)
+            
+            let xConstraint: NSLayoutConstraint
+            if index == 0 {
+                xConstraint = accountImageView.leadingAnchor.constraint(equalTo: avatarContainerView.leadingAnchor)
+            } else if index == accounts.count - 1 {
+                xConstraint = accountImageView.trailingAnchor.constraint(equalTo: avatarContainerView.trailingAnchor)
+            } else {
+                xConstraint = accountImageView.centerXAnchor.constraint(equalTo: avatarContainerView.centerXAnchor)
+            }
+            NSLayoutConstraint.activate([
+                accountImageView.widthAnchor.constraint(equalToConstant: avatarImageSize),
+                accountImageView.heightAnchor.constraint(equalToConstant: avatarImageSize),
+                accountImageView.centerYAnchor.constraint(equalTo: avatarContainerView.centerYAnchor),
+                xConstraint
+            ])
+            
+            let req = ImageCache.avatars.get(account.avatar) { [weak accountImageView] (_, image) in
+                DispatchQueue.main.async {
+                    accountImageView?.image = image
+                }
+            }
+            if let req = req {
+                avatarRequests.append(req)
+            }
+        }
+    }
+    
+    @objc private func preferencesChanged() {
+        avatarImageViews.forEach {
+            $0.layer.cornerRadius = Preferences.shared.avatarStyle.cornerRadius(for: $0)
+        }
+    }
+    
+    override func prepareForReuse() {
+        super.prepareForReuse()
+        
+        avatarRequests.forEach { $0.cancel() }
+    }
+    
+}

Tusker/Screens/Conversation/ExpandThreadTableViewCell.xib

@@ -0,0 +1,80 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<document type="com.apple.InterfaceBuilder3.CocoaTouch.XIB" version="3.0" toolsVersion="17701" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES">
+    <device id="retina6_1" orientation="portrait" appearance="light"/>
+    <dependencies>
+        <deployment identifier="iOS"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="17703"/>
+        <capability name="Safe area layout guides" minToolsVersion="9.0"/>
+        <capability name="System colors in document resources" minToolsVersion="11.0"/>
+        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
+    </dependencies>
+    <objects>
+        <placeholder placeholderIdentifier="IBFilesOwner" id="-1" userLabel="File's Owner"/>
+        <placeholder placeholderIdentifier="IBFirstResponder" id="-2" customClass="UIResponder"/>
+        <tableViewCell contentMode="scaleToFill" selectionStyle="default" indentationWidth="10" id="KGk-i7-Jjw" customClass="ExpandThreadTableViewCell" customModule="Tusker" customModuleProvider="target">
+            <rect key="frame" x="0.0" y="0.0" width="320" height="44"/>
+            <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMaxY="YES"/>
+            <tableViewCellContentView key="contentView" opaque="NO" clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="center" tableViewCell="KGk-i7-Jjw" id="H2p-sc-9uM">
+                <rect key="frame" x="0.0" y="0.0" width="320" height="44"/>
+                <autoresizingMask key="autoresizingMask"/>
+                <subviews>
+                    <stackView opaque="NO" contentMode="scaleToFill" alignment="center" spacing="8" translatesAutoresizingMaskIntoConstraints="NO" id="IXi-sc-YIw">
+                        <rect key="frame" x="16" y="0.0" width="173" height="44"/>
+                        <subviews>
+                            <view contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="eFB-F1-d3A">
+                                <rect key="frame" x="0.0" y="6" width="100" height="32"/>
+                                <constraints>
+                                    <constraint firstAttribute="height" constant="32" id="g9U-u7-718"/>
+                                    <constraint firstAttribute="width" constant="100" id="tiI-Rj-gjh"/>
+                                </constraints>
+                            </view>
+                            <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="2 replies" textAlignment="natural" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="Dcm-ll-GeE">
+                                <rect key="frame" x="108" y="12" width="65" height="20.5"/>
+                                <fontDescription key="fontDescription" type="system" pointSize="17"/>
+                                <color key="textColor" systemColor="systemBlueColor"/>
+                                <nil key="highlightedColor"/>
+                            </label>
+                        </subviews>
+                        <constraints>
+                            <constraint firstAttribute="height" constant="44" id="jk2-uV-FdO"/>
+                        </constraints>
+                    </stackView>
+                    <view contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="Kkt-hM-ScW">
+                        <rect key="frame" x="16" y="43.5" width="304" height="0.5"/>
+                        <color key="backgroundColor" systemColor="separatorColor"/>
+                        <constraints>
+                            <constraint firstAttribute="height" constant="0.5" id="Fkq-bT-IYv"/>
+                        </constraints>
+                    </view>
+                </subviews>
+                <constraints>
+                    <constraint firstAttribute="bottom" secondItem="Kkt-hM-ScW" secondAttribute="bottom" id="AvY-H1-0YN"/>
+                    <constraint firstItem="Kkt-hM-ScW" firstAttribute="leading" secondItem="H2p-sc-9uM" secondAttribute="leading" constant="16" id="E5g-hz-SLI"/>
+                    <constraint firstItem="IXi-sc-YIw" firstAttribute="top" secondItem="H2p-sc-9uM" secondAttribute="top" id="SRF-Zx-Y0R"/>
+                    <constraint firstAttribute="trailing" secondItem="Kkt-hM-ScW" secondAttribute="trailing" id="YML-R1-ezq"/>
+                    <constraint firstItem="IXi-sc-YIw" firstAttribute="leading" secondItem="H2p-sc-9uM" secondAttribute="leadingMargin" id="iD5-Av-ORS"/>
+                    <constraint firstAttribute="bottom" secondItem="IXi-sc-YIw" secondAttribute="bottom" id="kpD-6Q-qKi"/>
+                </constraints>
+            </tableViewCellContentView>
+            <viewLayoutGuide key="safeArea" id="njF-e1-oar"/>
+            <color key="backgroundColor" systemColor="secondarySystemBackgroundColor"/>
+            <connections>
+                <outlet property="avatarContainerView" destination="eFB-F1-d3A" id="xGo-40-nn7"/>
+                <outlet property="avatarContainerWidthConstraint" destination="tiI-Rj-gjh" id="34n-ev-EKi"/>
+                <outlet property="replyCountLabel" destination="Dcm-ll-GeE" id="E4m-xk-DiQ"/>
+            </connections>
+            <point key="canvasLocation" x="132" y="132"/>
+        </tableViewCell>
+    </objects>
+    <resources>
+        <systemColor name="secondarySystemBackgroundColor">
+            <color red="0.94901960784313721" green="0.94901960784313721" blue="0.96862745098039216" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
+        </systemColor>
+        <systemColor name="separatorColor">
+            <color red="0.23529411764705882" green="0.23529411764705882" blue="0.2627450980392157" alpha="0.28999999999999998" colorSpace="custom" customColorSpace="sRGB"/>
+        </systemColor>
+        <systemColor name="systemBlueColor">
+            <color red="0.0" green="0.47843137254901963" blue="1" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
+        </systemColor>
+    </resources>
+</document>

Tusker/TuskerNavigationDelegate.swift

@@ -12,6 +12,8 @@ import Pachyderm
 
 protocol TuskerNavigationDelegate: UIViewController {
     var apiController: MastodonController { get }
+    
+    func conversation(mainStatusID: String, state: StatusState) -> ConversationTableViewController
 }
 
 extension TuskerNavigationDelegate {
@@ -64,19 +66,16 @@ extension TuskerNavigationDelegate {
         }
     }
     
+    func conversation(mainStatusID: String, state: StatusState) -> ConversationTableViewController {
+        return ConversationTableViewController(for: mainStatusID, state: state, mastodonController: apiController)
+    }
+    
     func selected(status statusID: String) {
         self.selected(status: statusID, state: .unknown)
     }
     
     func selected(status statusID: String, state: StatusState) {
-        // todo: is this necessary? should the conversation main status cell prevent this
+        show(conversation(mainStatusID: statusID, state: state), sender: self)
-        // don't open if the conversation is the same as the current one
-        if let conversationController = self as? ConversationTableViewController,
-            conversationController.mainStatusID == statusID {
-            return
-        }
-        
-        show(ConversationTableViewController(for: statusID, state: state, mastodonController: apiController), sender: self)
     }
     
     func compose(editing draft: Draft) {

Tusker/Views/Status/BaseStatusTableViewCell.swift

@@ -38,6 +38,8 @@ class BaseStatusTableViewCell: UITableViewCell {
     @IBOutlet weak var favoriteButton: UIButton!
     @IBOutlet weak var reblogButton: UIButton!
     @IBOutlet weak var moreButton: UIButton!
+    private(set) var prevThreadLinkView: UIView?
+    private(set) var nextThreadLinkView: UIView?
     
     var statusID: String!
     var accountID: String!
@@ -278,6 +280,52 @@ class BaseStatusTableViewCell: UITableViewCell {
         displayNameLabel.updateForAccountDisplayName(account: account)
     }
     
+    func setShowThreadLinks(prev: Bool, next: Bool) {
+        if prev {
+            if let prevThreadLinkView = prevThreadLinkView {
+                prevThreadLinkView.isHidden = false
+            } else {
+                let view = UIView()
+                view.translatesAutoresizingMaskIntoConstraints = false
+                view.backgroundColor = tintColor.withAlphaComponent(0.5)
+                view.layer.cornerRadius = 2.5
+                view.layer.maskedCorners = [.layerMinXMaxYCorner, .layerMaxXMaxYCorner]
+                prevThreadLinkView = view
+                addSubview(view)
+                NSLayoutConstraint.activate([
+                    view.widthAnchor.constraint(equalToConstant: 5),
+                    view.centerXAnchor.constraint(equalTo: avatarImageView.centerXAnchor),
+                    view.topAnchor.constraint(equalTo: topAnchor),
+                    view.bottomAnchor.constraint(equalTo: avatarImageView.topAnchor, constant: -2),
+                ])
+            }
+        } else {
+            prevThreadLinkView?.isHidden = true
+        }
+        
+        if next {
+            if let nextThreadLinkView = nextThreadLinkView {
+                nextThreadLinkView.isHidden = false
+            } else {
+                let view = UIView()
+                view.translatesAutoresizingMaskIntoConstraints = false
+                view.backgroundColor = tintColor.withAlphaComponent(0.5)
+                view.layer.cornerRadius = 2.5
+                view.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
+                nextThreadLinkView = view
+                addSubview(view)
+                NSLayoutConstraint.activate([
+                    view.widthAnchor.constraint(equalToConstant: 5),
+                    view.centerXAnchor.constraint(equalTo: avatarImageView.centerXAnchor),
+                    view.topAnchor.constraint(equalTo: avatarImageView.bottomAnchor, constant: 2),
+                    view.bottomAnchor.constraint(equalTo: bottomAnchor),
+                ])
+            }
+        } else {
+            nextThreadLinkView?.isHidden = true
+        }
+    }
+    
     override func prepareForReuse() {
         super.prepareForReuse()
         

Tusker/en.lproj/Localizable.stringsdict

@@ -29,5 +29,21 @@
 			<string>%u people</string>
 		</dict>
 	</dict>
+	<key>expand threads count</key>
+	<dict>
+		<key>NSStringLocalizedFormatKey</key>
+		<string>%#@replies@</string>
+		<key>replies</key>
+		<dict>
+			<key>NSStringFormatSpecTypeKey</key>
+			<string>NSStringPluralRuleType</string>
+			<key>NSStringFormatValueTypeKey</key>
+			<string>u</string>
+			<key>one</key>
+			<string>1 reply</string>
+			<key>other</key>
+			<string>%u replies</string>
+		</dict>
+	</dict>
 </dict>
 </plist>