Convert edit list screen to collection view

Tusker/Screens/Lists/EditListAccountsViewController.swift

@@ -10,18 +10,21 @@ import UIKit
 import Pachyderm
 import Combine
 
-class EditListAccountsViewController: EnhancedTableViewController {
+class EditListAccountsViewController: UIViewController, CollectionViewController {
 
     private var list: List
-    let mastodonController: MastodonController
+    private let mastodonController: MastodonController
     
-    var changedAccounts = false
+    private var state = State.unloaded
     
-    var dataSource: DataSource!
+    private(set) var changedAccounts = false
-    var nextRange: RequestRange?
     
-    var searchResultsController: SearchResultsViewController!
+    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
-    var searchController: UISearchController!
+    var collectionView: UICollectionView! { view as? UICollectionView }
+    private var nextRange: RequestRange?
+    
+    private var searchResultsController: SearchResultsViewController!
+    private var searchController: UISearchController!
     
     private var listRenamedCancellable: AnyCancellable?
     
@@ -29,7 +32,7 @@ class EditListAccountsViewController: EnhancedTableViewController {
         self.list = list
         self.mastodonController = mastodonController
         
-        super.init(style: .plain)
+        super.init(nibName: nil, bundle: nil)
         
         listChanged()
         
@@ -46,29 +49,45 @@ class EditListAccountsViewController: EnhancedTableViewController {
         fatalError("init(coder:) has not been implemeneted")
     }
     
+    override func loadView() {
+        var config = UICollectionLayoutListConfiguration(appearance: .grouped)
+        config.itemSeparatorHandler = { [unowned self] indexPath, sectionConfig in
+            var config = sectionConfig
+            switch dataSource.itemIdentifier(for: indexPath)! {
+            case .loadingIndicator:
+                config.topSeparatorVisibility = .hidden
+                config.bottomSeparatorVisibility = .hidden
+            case .account(id: _):
+                config.topSeparatorInsets = TimelineStatusCollectionViewCell.separatorInsets
+                config.bottomSeparatorInsets = TimelineStatusCollectionViewCell.separatorInsets
+            }
+            return config
+        }
+        config.trailingSwipeActionsConfigurationProvider = { [unowned self] indexPath in
+            switch dataSource.itemIdentifier(for: indexPath) {
+            case .account(id: let id):
+                let remove = UIContextualAction(style: .destructive, title: "Remove") { [unowned self] _, _, completion in
+                    Task {
+                        await self.removeAccount(id: id)
+                        completion(true)
+                    }
+                }
+                return UISwipeActionsConfiguration(actions: [remove])
+            default:
+                return nil
+            }
+        }
+        let layout = UICollectionViewCompositionalLayout.list(using: config)
+        view = UICollectionView(frame: .zero, collectionViewLayout: layout)
+        collectionView.delegate = self
+        collectionView.allowsSelection = false
+        collectionView.backgroundColor = .appGroupedBackground
+        dataSource = createDataSource()
+    }
+    
     override func viewDidLoad() {
         super.viewDidLoad()
         
-        tableView.register(UINib(nibName: "AccountTableViewCell", bundle: .main), forCellReuseIdentifier: "accountCell")
-        
-        tableView.rowHeight = UITableView.automaticDimension
-        tableView.estimatedRowHeight = 66
-        tableView.allowsSelection = false
-        tableView.backgroundColor = .appGroupedBackground
-        
-        dataSource = DataSource(tableView: tableView, cellProvider: { (tableView, indexPath, item) -> UITableViewCell? in
-            guard case let .account(id) = item else { fatalError() }
-            
-            let cell = tableView.dequeueReusableCell(withIdentifier: "accountCell", for: indexPath) as! AccountTableViewCell
-            cell.delegate = self
-            cell.updateUI(accountID: id)
-            cell.configurationUpdateHandler = { cell, state in
-                cell.backgroundConfiguration = .appListGroupedCell(for: state)
-            }
-            return cell
-        })
-        dataSource.editListAccountsController = self
-        
         searchResultsController = SearchResultsViewController(mastodonController: mastodonController, scope: .people)
         searchResultsController.following = true
         searchResultsController.delegate = self
@@ -87,6 +106,33 @@ class EditListAccountsViewController: EnhancedTableViewController {
         }
         
         navigationItem.rightBarButtonItem = UIBarButtonItem(title: NSLocalizedString("Rename", comment: "rename list button title"), style: .plain, target: self, action: #selector(renameButtonPressed))
+    }
+    
+    private func createDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
+        let loadingCell = UICollectionView.CellRegistration<LoadingCollectionViewCell, Void> { cell, indexPath, itemIdentifier in
+            cell.indicator.startAnimating()
+        }
+        let accountCell = UICollectionView.CellRegistration<AccountCollectionViewCell, String> { [unowned self] cell, indexPath, itemIdentifier in
+            cell.delegate = self
+            cell.updateUI(accountID: itemIdentifier)
+            cell.configurationUpdateHandler = { cell, state in
+                cell.backgroundConfiguration = .appListGroupedCell(for: state)
+            }
+        }
+        return UICollectionViewDiffableDataSource(collectionView: collectionView) { collectionView, indexPath, itemIdentifier in
+            switch itemIdentifier {
+            case .loadingIndicator:
+                return collectionView.dequeueConfiguredReusableCell(using: loadingCell, for: indexPath, item: ())
+            case .account(id: let id):
+                return collectionView.dequeueConfiguredReusableCell(using: accountCell, for: indexPath, item: id)
+            }
+        }
+    }
+    
+    override func viewWillAppear(_ animated: Bool) {
+        super.viewWillAppear(animated)
+        
+        clearSelectionOnAppear(animated: animated)
                 
         Task {
             await loadAccounts()
@@ -97,10 +143,21 @@ class EditListAccountsViewController: EnhancedTableViewController {
         title = String(format: NSLocalizedString("Edit %@", comment: "edit list screen title"), list.title)
     }
     
-    func loadAccounts() async {
+    @MainActor
+    private func loadAccounts() async {
+        guard state == .unloaded else { return }
+        
+        state = .loading
+        
+        async let results = try await mastodonController.run(List.getAccounts(list.id))
+        
+        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
+        snapshot.appendSections([.accounts])
+        snapshot.appendItems([.loadingIndicator])
+        await dataSource.apply(snapshot)
+        
         do {
-            let request = List.getAccounts(list.id)
+            let (accounts, pagination) = try await results
-            let (accounts, pagination) = try await mastodonController.run(request)
             self.nextRange = pagination?.older
             
             await withCheckedContinuation { continuation in
@@ -109,20 +166,61 @@ class EditListAccountsViewController: EnhancedTableViewController {
                 }
             }
             
-            var snapshot = self.dataSource.snapshot()
+            var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
-            if snapshot.indexOfSection(.accounts) == nil {
             snapshot.appendSections([.accounts])
-            } else {
-                snapshot.deleteItems(snapshot.itemIdentifiers(inSection: .accounts))
-            }
             snapshot.appendItems(accounts.map { .account(id: $0.id) })
             await dataSource.apply(snapshot)
+            
+            state = .loaded
         } catch {
             let config = ToastConfiguration(from: error, with: "Error Loading Accounts", in: self) { [unowned self] toast in
                 toast.dismissToast(animated: true)
                 await self.loadAccounts()
             }
             self.showToast(configuration: config, animated: true)
+            
+            state = .unloaded
+            await dataSource.apply(.init())
+        }
+    }
+    
+    private func loadNextPage() async {
+        guard state == .loaded,
+              let nextRange else { return }
+        
+        state = .loading
+        
+        async let results = try await mastodonController.run(List.getAccounts(list.id, range: nextRange))
+        
+        let origSnapshot = dataSource.snapshot()
+        var snapshot = origSnapshot
+        snapshot.appendItems([.loadingIndicator])
+        await dataSource.apply(snapshot)
+        
+        do {
+            let (accounts, pagination) = try await results
+            self.nextRange = pagination?.older
+            
+            await withCheckedContinuation { continuation in
+                mastodonController.persistentContainer.addAll(accounts: accounts) {
+                    continuation.resume()
+                }
+            }
+            
+            var snapshot = origSnapshot
+            snapshot.appendItems(accounts.map { .account(id: $0.id) })
+            await dataSource.apply(snapshot)
+            
+            state = .loaded
+        } catch {
+            let config = ToastConfiguration(from: error, with: "Error Loading Accounts", in: self) { [unowned self] toast in
+                toast.dismissToast(animated: true)
+                await self.loadNextPage()
+            }
+            self.showToast(configuration: config, animated: true)
+            
+            state = .loaded
+            await dataSource.apply(origSnapshot)
         }
     }
     
@@ -157,12 +255,6 @@ class EditListAccountsViewController: EnhancedTableViewController {
         }
     }
 
-    // MARK: - Table view delegate
-
-    override func tableView(_ tableView: UITableView, editingStyleForRowAt indexPath: IndexPath) -> UITableViewCell.EditingStyle {
-        return .delete
-    }
-    
     // MARK: - Interaction
     
     @objc func renameButtonPressed() {
@@ -171,29 +263,31 @@ class EditListAccountsViewController: EnhancedTableViewController {
     
 }
 
+extension EditListAccountsViewController {
+    enum State {
+        case unloaded
+        case loading
+        case loaded
+        case loadingOlder
+    }
+}
+
 extension EditListAccountsViewController {
     enum Section: Hashable {
         case accounts
     }
     enum Item: Hashable {
+        case loadingIndicator
         case account(id: String)
     }
-    
-    class DataSource: UITableViewDiffableDataSource<Section, Item> {
-        weak var editListAccountsController: EditListAccountsViewController?
-        
-        override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
-            return true
-        }
-        
-        override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
-            guard editingStyle == .delete,
-                case let .account(id) = itemIdentifier(for: indexPath) else {
-                return
 }
 
+extension EditListAccountsViewController: UICollectionViewDelegate {
+    func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
+        if state == .loaded,
+        indexPath.item == collectionView.numberOfItems(inSection: indexPath.section) - 1 {
             Task {
-                await self.editListAccountsController?.removeAccount(id: id)
+                await loadNextPage()
             }
         }
     }