Add pagination to status actions account list

Tusker/Screens/Status Action Account List/StatusActionAccountListCollectionViewController.swift

@@ -11,6 +11,8 @@ import Pachyderm
 
 class StatusActionAccountListCollectionViewController: UIViewController, CollectionViewController {
     
+    private let statusID: String
+    private let actionType: StatusActionAccountListViewController.ActionType
     private let mastodonController: MastodonController
     
     /// If `true`, a warning will be shown below the account list describing that the total favs/reblogs may be innacurate.
@@ -21,12 +23,17 @@ class StatusActionAccountListCollectionViewController: UIViewController, Collect
     }
     private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
     
+    private var state: State = .unloaded
+    private var older: RequestRange?
+    
     /**
      Creates a new view controller showing the accounts that performed the given action on the given status.
      
      - Parameter mastodonController The `MastodonController` instance this view controller uses.
      */
-    init(mastodonController: MastodonController) {
+    init(statusID: String, actionType: StatusActionAccountListViewController.ActionType, mastodonController: MastodonController) {
+        self.statusID = statusID
+        self.actionType = actionType
         self.mastodonController = mastodonController
         
         super.init(nibName: nil, bundle: nil)
@@ -38,6 +45,18 @@ class StatusActionAccountListCollectionViewController: UIViewController, Collect
     }
     
     override func loadView() {
+        var accountsConfig = UICollectionLayoutListConfiguration(appearance: .grouped)
+        accountsConfig.itemSeparatorHandler = { [unowned self] indexPath, sectionConfig in
+            guard let item = self.dataSource.itemIdentifier(for: indexPath) else {
+                return sectionConfig
+            }
+            var config = sectionConfig
+            if item.hideSeparators {
+                config.topSeparatorVisibility = .hidden
+                config.bottomSeparatorVisibility = .hidden
+            }
+            return config
+        }
         let layout = UICollectionViewCompositionalLayout { [unowned self] sectionIndex, environment in
             switch dataSource.sectionIdentifier(for: sectionIndex)! {
             case .status:
@@ -51,7 +70,7 @@ class StatusActionAccountListCollectionViewController: UIViewController, Collect
                 }
                 return NSCollectionLayoutSection.list(using: config, layoutEnvironment: environment)
             case .accounts:
-                return NSCollectionLayoutSection.list(using: .init(appearance: .grouped), layoutEnvironment: environment)
+                return NSCollectionLayoutSection.list(using: accountsConfig, layoutEnvironment: environment)
             }
         }
         view = UICollectionView(frame: .zero, collectionViewLayout: layout)
@@ -70,12 +89,17 @@ class StatusActionAccountListCollectionViewController: UIViewController, Collect
             cell.delegate = self
             cell.updateUI(accountID: item)
         }
+        let loadingCell = UICollectionView.CellRegistration<LoadingCollectionViewCell, Void> { cell, indexPath, item in
+            cell.indicator.startAnimating()
+        }
         let dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView) { collectionView, indexPath, itemIdentifier in
             switch itemIdentifier {
             case .status(let id, let state):
                 return collectionView.dequeueConfiguredReusableCell(using: statusCell, for: indexPath, item: (id, state))
             case .account(let id):
                 return collectionView.dequeueConfiguredReusableCell(using: accountCell, for: indexPath, item: id)
+            case .loadingIndicator:
+                return collectionView.dequeueConfiguredReusableCell(using: loadingCell, for: indexPath, item: ())
             }
         }
         let sectionHeaderCell = UICollectionView.SupplementaryRegistration<UICollectionViewListCell>(elementKind: UICollectionView.elementKindSectionFooter) { (headerView, collectionView, indexPath) in
@@ -93,6 +117,12 @@ class StatusActionAccountListCollectionViewController: UIViewController, Collect
         super.viewWillAppear(animated)
         
         clearSelectionOnAppear(animated: animated)
+        
+        if case .unloaded = state {
+            Task {
+                await loadAccounts()
+            }
+        }
     }
     
     func addStatus(_ status: StatusMO, state: CollapseState) {
@@ -104,12 +134,115 @@ class StatusActionAccountListCollectionViewController: UIViewController, Collect
         dataSource.apply(snapshot, animatingDifferences: false)
     }
     
-    func addAccounts(_ accountIDs: [String], animated: Bool) {
+    func setAccounts(_ accountIDs: [String], animated: Bool) {
+        guard case .unloaded = state else {
+            return
+        }
         var snapshot = dataSource.snapshot()
         snapshot.appendItems(accountIDs.map { .account($0) }, toSection: .accounts)
         dataSource.apply(snapshot, animatingDifferences: animated)
+        self.state = .loaded
     }
     
+    private func request(for range: RequestRange) -> Request<[Account]> {
+        switch actionType {
+        case .favorite:
+            return Status.getFavourites(statusID, range: range)
+        case .reblog:
+            return Status.getReblogs(statusID, range: range)
+        }
+    }
+    
+    func apply(snapshot: NSDiffableDataSourceSnapshot<Section, Item>) async {
+        await Task { @MainActor in
+            self.dataSource.apply(snapshot)
+        }.value
+    }
+    
+    @MainActor
+    private func loadAccounts() async {
+        guard case .unloaded = state else {
+            return
+        }
+        self.state = .loadingInitial
+        
+        var snapshot = dataSource.snapshot()
+        snapshot.appendItems([.loadingIndicator], toSection: .accounts)
+        await apply(snapshot: snapshot)
+        
+        do {
+            let (accounts, pagination) = try await mastodonController.run(request(for: .default))
+            await mastodonController.persistentContainer.addAll(accounts: accounts)
+            
+            guard case .loadingInitial = self.state else {
+                return
+            }
+            self.state = .loaded
+            self.older = pagination?.older
+            
+            var snapshot = dataSource.snapshot()
+            snapshot.deleteItems([.loadingIndicator])
+            snapshot.appendItems(accounts.map { .account($0.id) }, toSection: .accounts)
+            await apply(snapshot: snapshot)
+            
+        } catch {
+            self.state = .unloaded
+            
+            let config = ToastConfiguration(from: error, with: "Error Loading Accounts", in: self) { toast in
+                toast.dismissToast(animated: true)
+                await self.loadAccounts()
+            }
+            self.showToast(configuration: config, animated: true)
+        }
+    }
+    
+    @MainActor
+    private func loadOlder() async {
+        guard case .loaded = state,
+              let older else {
+            return
+        }
+        self.state = .loadingOlder
+        
+        var snapshot = self.dataSource.snapshot()
+        snapshot.appendItems([.loadingIndicator], toSection: .accounts)
+        await apply(snapshot: snapshot)
+        
+        do {
+            try! await Task.sleep(nanoseconds: 2 * NSEC_PER_SEC)
+            let (accounts, pagination) = try await mastodonController.run(request(for: older))
+            await mastodonController.persistentContainer.addAll(accounts: accounts)
+            
+            guard case .loadingOlder = self.state else {
+                return
+            }
+            self.state = .loaded
+            self.older = pagination?.older
+            
+            var snapshot = dataSource.snapshot()
+            snapshot.deleteItems([.loadingIndicator])
+            snapshot.appendItems(accounts.map { .account($0.id) }, toSection: .accounts)
+            await apply(snapshot: snapshot)
+            
+        } catch {
+            self.state = .loaded
+            
+            let config = ToastConfiguration(from: error, with: "Error Loading More", in: self) { [unowned self] toast in
+                toast.dismissToast(animated: true)
+                await self.loadOlder()
+            }
+            self.showToast(configuration: config, animated: true)
+        }
+    }
+}
+
+extension StatusActionAccountListCollectionViewController {
+    enum State {
+        case unloaded
+        case loadingInitial
+        case loaded
+        case loadingOlder
+    }
 }
 
 extension StatusActionAccountListCollectionViewController {
@@ -120,6 +253,16 @@ extension StatusActionAccountListCollectionViewController {
     enum Item: Hashable {
         case status(String, CollapseState)
         case account(String)
+        case loadingIndicator
+        
+        var hideSeparators: Bool {
+            switch self {
+            case .loadingIndicator:
+                return true
+            default:
+                return false
+            }
+        }
         
         static func ==(lhs: Item, rhs: Item) -> Bool {
             switch (lhs, rhs) {
@@ -127,6 +270,8 @@ extension StatusActionAccountListCollectionViewController {
                 return a == b
             case (.account(let a), .account(let b)):
                 return a == b
+            case (.loadingIndicator, .loadingIndicator):
+                return true
             default:
                 return false
             }
@@ -140,12 +285,23 @@ extension StatusActionAccountListCollectionViewController {
             case .account(let id):
                 hasher.combine(1)
                 hasher.combine(id)
+            case .loadingIndicator:
+                hasher.combine(2)
             }
         }
     }
 }
 
 extension StatusActionAccountListCollectionViewController: UICollectionViewDelegate {
+    func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
+        if indexPath.section == collectionView.numberOfSections - 1,
+           indexPath.row == collectionView.numberOfItems(inSection: indexPath.section) - 1 {
+            Task {
+                await self.loadOlder()
+            }
+        }
+    }
+    
     func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
         switch dataSource.itemIdentifier(for: indexPath) {
         case nil:
@@ -154,6 +310,8 @@ extension StatusActionAccountListCollectionViewController: UICollectionViewDeleg
             selected(status: id, state: state.copy())
         case .account(let id):
             selected(account: id)
+        case .loadingIndicator:
+            return
         }
     }
     
@@ -171,6 +329,8 @@ extension StatusActionAccountListCollectionViewController: UICollectionViewDeleg
             } actionProvider: { _ in
                 UIMenu(children: self.actionsForProfile(accountID: id, source: .view(cell)))
             }
+        case .loadingIndicator:
+            return nil
         }
     }
     
@@ -203,6 +363,8 @@ extension StatusActionAccountListCollectionViewController: UICollectionViewDragD
             let activity = UserActivityManager.showProfileActivity(id: account.id, accountID: currentAccountID)
             activity.displaysAuxiliaryScene = true
             provider.registerObject(activity, visibility: .all)
+        case .loadingIndicator:
+            return []
         }
         return [UIDragItem(itemProvider: provider)]
     }

Tusker/Screens/Status Action Account List/StatusActionAccountListViewController.swift

@@ -95,8 +95,10 @@ class StatusActionAccountListViewController: UIViewController {
     override func viewWillAppear(_ animated: Bool) {
         super.viewWillAppear(animated)
         
-        Task {
+        if case .unloaded = state {
-            await loadStatus()
+            Task {
+                await loadStatus()
+            }
         }
     }
     
@@ -143,45 +145,13 @@ class StatusActionAccountListViewController: UIViewController {
     }
     
     private func statusLoaded(_ status: StatusMO) async {
-        let vc = StatusActionAccountListCollectionViewController(mastodonController: mastodonController)
+        let vc = StatusActionAccountListCollectionViewController(statusID: statusID, actionType: actionType, mastodonController: mastodonController)
         vc.addStatus(status, state: statusState)
         vc.showInacurateCountWarning = showInacurateCountWarning
-        state = .displaying(vc)
-        
         if let accountIDs {
-            vc.addAccounts(accountIDs, animated: false)
+            vc.setAccounts(accountIDs, animated: false)
-        } else {
-            await loadAccounts(list: vc)
-        }
-    }
-    
-    private func loadAccounts(list: StatusActionAccountListCollectionViewController) async {
-        let request: Request<[Account]>
-        switch actionType {
-        case .favorite:
-            request = Status.getFavourites(statusID)
-        case .reblog:
-            request = Status.getReblogs(statusID)
-        }
-        do {
-            // TODO: pagination
-            let (accounts, _) = try await mastodonController.run(request)
-            
-            await withCheckedContinuation { continuation in
-                mastodonController.persistentContainer.addAll(accounts: accounts) {
-                    continuation.resume()
-                }
-            }
-            
-            list.addAccounts(accounts.map(\.id), animated: true)
-            
-        } catch {
-            let config = ToastConfiguration(from: error, with: "Error Loading Accounts", in: self) { toast in
-                toast.dismissToast(animated: true)
-                await self.loadAccounts(list: list)
-            }
-            self.showToast(configuration: config, animated: true)
         }
+        state = .displaying(vc)
     }
     
     private func showStatusNotFound() {