Add DiffableTimelineLikeTableViewController

Tusker.xcodeproj/project.pbxproj

@@ -155,6 +155,7 @@
 		D6531DEE246B81C9000F9538 /* GifvAttachmentView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6531DED246B81C9000F9538 /* GifvAttachmentView.swift */; };
 		D6531DF0246B867E000F9538 /* GifvAttachmentViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6531DEF246B867E000F9538 /* GifvAttachmentViewController.swift */; };
 		D6538945214D6D7500E3CEFC /* TableViewSwipeActionProvider.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6538944214D6D7500E3CEFC /* TableViewSwipeActionProvider.swift */; };
+		D653F411267D1E32004E32B1 /* DiffableTimelineLikeTableViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D653F410267D1E32004E32B1 /* DiffableTimelineLikeTableViewController.swift */; };
 		D65C6BF525478A9C00A6E89C /* BackgroundableViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D65C6BF425478A9C00A6E89C /* BackgroundableViewController.swift */; };
 		D65F613423AEAB6600F3CFD3 /* OnboardingTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D65F613323AEAB6600F3CFD3 /* OnboardingTests.swift */; };
 		D6620ACE2511A0ED00312CA0 /* StatusStateResolver.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6620ACD2511A0ED00312CA0 /* StatusStateResolver.swift */; };
@@ -553,6 +554,7 @@
 		D6531DED246B81C9000F9538 /* GifvAttachmentView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GifvAttachmentView.swift; sourceTree = "<group>"; };
 		D6531DEF246B867E000F9538 /* GifvAttachmentViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GifvAttachmentViewController.swift; sourceTree = "<group>"; };
 		D6538944214D6D7500E3CEFC /* TableViewSwipeActionProvider.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TableViewSwipeActionProvider.swift; sourceTree = "<group>"; };
+		D653F410267D1E32004E32B1 /* DiffableTimelineLikeTableViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DiffableTimelineLikeTableViewController.swift; sourceTree = "<group>"; };
 		D65C6BF425478A9C00A6E89C /* BackgroundableViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BackgroundableViewController.swift; sourceTree = "<group>"; };
 		D65F612D23AE990C00F3CFD3 /* Embassy.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; path = Embassy.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		D65F613023AE99E000F3CFD3 /* Ambassador.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; path = Ambassador.framework; sourceTree = BUILT_PRODUCTS_DIR; };
@@ -1485,6 +1487,7 @@
 				D65C6BF425478A9C00A6E89C /* BackgroundableViewController.swift */,
 				D6B81F3B2560365300F6E31D /* RefreshableViewController.swift */,
 				D65234C8256189D0001AF9CF /* TimelineLikeTableViewController.swift */,
+				D653F410267D1E32004E32B1 /* DiffableTimelineLikeTableViewController.swift */,
 				D625E4812588262A0074BB2B /* DraggableTableViewCell.swift */,
 				D6A6C10425B6138A00298D0F /* StatusTablePrefetching.swift */,
 			);
@@ -2151,6 +2154,7 @@
 				D626493823C0FD0000612E6E /* AllPhotosTableViewCell.swift in Sources */,
 				D627943B23A55BA600D38C68 /* NavigableTableViewCell.swift in Sources */,
 				D6333B792139AEFD00CE884A /* Date+TimeAgo.swift in Sources */,
+				D653F411267D1E32004E32B1 /* DiffableTimelineLikeTableViewController.swift in Sources */,
 				D6C82B5625C5F3F20017F1E6 /* ExpandThreadTableViewCell.swift in Sources */,
 				D686BBE324FBF8110068E6AA /* WrappedProgressView.swift in Sources */,
 				D620483423D3801D008A63EF /* LinkTextView.swift in Sources */,

Tusker/Screens/Utilities/DiffableTimelineLikeTableViewController.swift

@@ -0,0 +1,268 @@
+//
+//  DiffableTimelineLikeTableViewController.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 6/18/21.
+//  Copyright © 2021 Shadowfacts. All rights reserved.
+//
+
+import UIKit
+import Pachyderm
+
+class DiffableTimelineLikeTableViewController<Section: Hashable & CaseIterable, Item: Hashable>: EnhancedTableViewController, RefreshableViewController {
+    
+    typealias Snapshot = NSDiffableDataSourceSnapshot<Section, Item>
+    typealias LoadResult = Result<Snapshot, LoadError>
+    
+    private let pageSize = 20
+    
+    private(set) var state = State.unloaded
+    private var lastLastVisibleRow: IndexPath?
+    
+    private(set) var dataSource: UITableViewDiffableDataSource<Section, Item>!
+    
+    init() {
+        super.init(style: .plain)
+        
+        addKeyCommand(MenuController.refreshCommand(discoverabilityTitle: Self.refreshCommandTitle()))
+    }
+    
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+    
+    override func viewDidLoad() {
+        super.viewDidLoad()
+        
+        dataSource = UITableViewDiffableDataSource(tableView: tableView, cellProvider: self.cellProvider)
+        
+        tableView.rowHeight = UITableView.automaticDimension
+        tableView.estimatedRowHeight = 140
+        
+        #if !targetEnvironment(macCatalyst)
+        self.refreshControl = UIRefreshControl()
+        self.refreshControl!.addTarget(self, action: #selector(refresh), for: .valueChanged)
+        #endif
+        
+        if let prefetchSource = self as? UITableViewDataSourcePrefetching {
+            tableView.prefetchDataSource = prefetchSource
+        }
+    }
+    
+    override func viewWillAppear(_ animated: Bool) {
+        super.viewWillAppear(animated)
+        
+        loadInitial()
+    }
+    
+    override func viewDidDisappear(_ animated: Bool) {
+        super.viewDidDisappear(animated)
+        
+        pruneOffscreenRows()
+    }
+    
+    class func refreshCommandTitle() -> String {
+        return "Refresh"
+    }
+    
+    private func pruneOffscreenRows() {
+        guard let lastVisibleRow = lastLastVisibleRow else {
+            return
+        }
+        
+        var snapshot = dataSource.snapshot()
+        
+        let lastVisibleRowSection = snapshot.sectionIdentifiers[lastVisibleRow.section]
+        
+        let contentSections = snapshot.sectionIdentifiers.filter { timelineContentSections().contains($0) }
+        
+        guard let lastVisibleContentSectionIndex = contentSections.lastIndex(of: lastVisibleRowSection) else {
+            return
+        }
+        
+        if lastVisibleContentSectionIndex < contentSections.count - 1 {
+            // there are more content sections below the current last visible one
+            
+            let sectionsToRemove = contentSections[lastVisibleContentSectionIndex...]
+            snapshot.deleteSections(Array(sectionsToRemove))
+            
+            willRemoveItems(sectionsToRemove.flatMap(snapshot.itemIdentifiers(inSection:)))
+        } else if lastVisibleContentSectionIndex == contentSections.count - 1 {
+            let items = snapshot.itemIdentifiers(inSection: lastVisibleRowSection)
+            
+            if lastVisibleRow.row < items.count - pageSize {
+                let itemsToRemove = Array(items.suffix(pageSize))
+                snapshot.deleteItems(itemsToRemove)
+                
+                willRemoveItems(itemsToRemove)
+            } else {
+                return
+            }
+        } else {
+            return
+        }
+        
+        dataSource.apply(snapshot, animatingDifferences: false)
+    }
+    
+    private func loadInitial() {
+        guard state == .unloaded else { return }
+        // set loaded immediately so we don't trigger another request while the current one is running
+        state = .loadingInitial
+        
+        loadInitialItems() { result in
+            guard case let .success(snapshot) = result else {
+                self.state = .unloaded
+                return
+            }
+            DispatchQueue.main.async {
+                self.dataSource.apply(snapshot, animatingDifferences: false)
+                self.state = .loaded
+            }
+       }
+    }
+    
+    func reloadInitial() {
+        state = .unloaded
+        loadInitial()
+    }
+    
+    func loadOlder() {
+        guard state != .loadingOlder else { return }
+        
+        state = .loadingOlder
+        
+        loadOlderItems(currentSnapshot: dataSource.snapshot()) { result in
+            guard case let .success(snapshot) = result else {
+                self.state = .loaded
+                return
+            }
+            DispatchQueue.main.async {
+                self.dataSource.apply(snapshot, animatingDifferences: false)
+                self.state = .loaded
+            }
+        }
+    }
+    
+    func cellHeightChanged() {
+        // causes the table view to recalculate the cell heights
+        tableView.beginUpdates()
+        tableView.endUpdates()
+    }
+    
+    // MARK: - UITableViewDelegate
+    
+    override func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
+        // this assumes that indexPathsForVisibleRows is always in order
+        lastLastVisibleRow = tableView.indexPathsForVisibleRows?.last
+        
+        if indexPath.section == tableView.numberOfSections - 1,
+           indexPath.row == tableView.numberOfRows(inSection: indexPath.section) - 1 {
+            
+            loadOlder()
+        }
+    }
+    
+    override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
+        return true
+    }
+    
+    override func tableView(_ tableView: UITableView, leadingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
+        return (tableView.cellForRow(at: indexPath) as? TableViewSwipeActionProvider)?.leadingSwipeActionsConfiguration()
+    }
+    
+    override func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
+        return (tableView.cellForRow(at: indexPath) as? TableViewSwipeActionProvider)?.trailingSwipeActionsConfiguration()
+    }
+    
+    // MARK: - RefreshableViewController
+    
+    func refresh() {
+        guard state != .loadingNewer else { return }
+        
+        state = .loadingNewer
+        
+        let snapshot = dataSource.snapshot()
+        
+        var item: Item? = nil
+        for section in timelineContentSections() {
+            if let first = snapshot.itemIdentifiers(inSection: section).first {
+                item = first
+                break
+            }
+        }
+        
+        loadNewerItems(currentSnapshot: snapshot) { result in
+            guard case let .success(snapshot) = result else {
+                DispatchQueue.main.async {
+                    self.refreshControl?.endRefreshing()
+                    self.state = .loaded
+                }
+                return
+            }
+            
+            DispatchQueue.main.async {
+                self.refreshControl?.endRefreshing()
+                self.dataSource.apply(snapshot, animatingDifferences: false)
+                self.state = .loaded
+
+                if let item = item,
+                   let indexPath = self.dataSource.indexPath(for: item) {
+                    // maintain the current position in the list (don't scroll to top)
+                    self.tableView.scrollToRow(at: indexPath, at: .top, animated: false)
+                }
+            }
+        }
+    }
+    
+    // MARK: - Subclass Methods
+    
+    func cellProvider(_ tableView: UITableView, _ indexPath: IndexPath, _ item: Item) -> UITableViewCell? {
+        fatalError("cellProvider(_:_:_:) must be implemented by subclasses")
+    }
+    
+    func loadInitialItems(completion: @escaping (LoadResult) -> Void) {
+        fatalError("loadInitialItems(completion:) must be implemented by subclasses")
+    }
+    
+    func loadOlderItems(currentSnapshot: Snapshot, completion: @escaping (LoadResult) -> Void) {
+        fatalError("loadOlderItesm(completion:) must be implemented by subclasses")
+    }
+    
+    func loadNewerItems(currentSnapshot: Snapshot, completion: @escaping (LoadResult) -> Void) {
+        fatalError("loadNewerItems(completion:) must be implemented by subclasses")
+    }
+    
+    func timelineContentSections() -> Section.AllCases {
+        return Section.allCases
+    }
+    
+    func willRemoveItems(_ items: [Item]) {
+    }
+
+}
+
+extension DiffableTimelineLikeTableViewController {
+    enum State: Equatable {
+        case unloaded
+        case loadingInitial
+        case loaded
+        case loadingNewer
+        case loadingOlder
+    }
+}
+
+extension DiffableTimelineLikeTableViewController {
+    enum LoadError: LocalizedError {
+        case noClient
+        case noOlder
+        case noNewer
+        case client(Client.Error)
+    }
+}
+
+extension DiffableTimelineLikeTableViewController: BackgroundableViewController {
+    func sceneDidEnterBackground() {
+        pruneOffscreenRows()
+    }
+}

Tusker/Screens/Utilities/TimelineLikeTableViewController.swift

@@ -9,8 +9,8 @@
 import UIKit
 
 /// A table view controller that manages common functionality  between timeline-like UIs.
-// For example, this class handles loading new items when the user scrolls to the end,
+/// For example, this class handles loading new items when the user scrolls to the end,
-// refreshing, and pruning offscreen rows automatically.
+/// refreshing, and pruning offscreen rows automatically.
 class TimelineLikeTableViewController<Item>: EnhancedTableViewController, RefreshableViewController {
 
     private(set) var loaded = false