Add infinite scrolling to trending hashtags screen

See #355

Packages/Pachyderm/Sources/Pachyderm/Client.swift

@@ -417,16 +417,28 @@ public class Client {
     }
     
     // MARK: - Instance
-    public static func getTrendingHashtags(limit: Int? = nil) -> Request<[Hashtag]> {
+    public static func getTrendingHashtagsDeprecated(limit: Int? = nil, offset: Int? = nil) -> Request<[Hashtag]> {
-        let parameters: [Parameter]
+        var parameters: [Parameter] = []
-        if let limit = limit {
+        if let limit {
-            parameters = ["limit" => limit]
+            parameters.append("limit" => limit)
-        } else {
+        }
-            parameters = []
+        if let offset {
+            parameters.append("offset" => offset)
         }
         return Request<[Hashtag]>(method: .get, path: "/api/v1/trends", queryParameters: parameters)
     }
     
+    public static func getTrendingHashtags(limit: Int? = nil, offset: Int? = nil) -> Request<[Hashtag]> {
+        var parameters: [Parameter] = []
+        if let limit {
+            parameters.append("limit" => limit)
+        }
+        if let offset {
+            parameters.append("offset" => offset)
+        }
+        return Request<[Hashtag]>(method: .get, path: "/api/v1/trends/tags", queryParameters: parameters)
+    }
+    
     public static func getTrendingStatuses(limit: Int? = nil) -> Request<[Status]> {
         let parameters: [Parameter]
         if let limit = limit {

Tusker/Screens/Explore/TrendingHashtagsViewController.swift

@@ -9,6 +9,7 @@
 import UIKit
 import Pachyderm
 import WebURLFoundationExtras
+import Combine
 
 class TrendingHashtagsViewController: UIViewController {
 
@@ -17,6 +18,9 @@ class TrendingHashtagsViewController: UIViewController {
     private var collectionView: UICollectionView!
     private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
     
+    private var state = State.unloaded
+    private var confirmLoadMore = PassthroughSubject<Void, Never>()
+    
     init(mastodonController: MastodonController) {
         self.mastodonController = mastodonController
         
@@ -32,9 +36,21 @@ class TrendingHashtagsViewController: UIViewController {
 
         title = NSLocalizedString("Trending Hashtags", comment: "trending hashtags screen title")
         
-        view.backgroundColor = .systemGroupedBackground
+        view.backgroundColor = .appGroupedBackground
         
-        let config = UICollectionLayoutListConfiguration(appearance: .grouped)
+        var config = UICollectionLayoutListConfiguration(appearance: .grouped)
+        config.backgroundColor = .appGroupedBackground
+        config.itemSeparatorHandler = { [unowned self] indexPath, sectionConfig in
+            guard let item = dataSource.itemIdentifier(for: indexPath) else {
+                return sectionConfig
+            }
+            var config = sectionConfig
+            if item.hideSeparators {
+                config.topSeparatorVisibility = .hidden
+                config.bottomSeparatorVisibility = .hidden
+            }
+            return config
+        }
         let layout = UICollectionViewCompositionalLayout.list(using: config)
         collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
         collectionView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
@@ -43,14 +59,24 @@ class TrendingHashtagsViewController: UIViewController {
         collectionView.allowsFocus = true
         view.addSubview(collectionView)
         
-        let registration = UICollectionView.CellRegistration<TrendingHashtagCollectionViewCell, Hashtag> { cell, indexPath, hashtag in
+        let loadingCell = UICollectionView.CellRegistration<LoadingCollectionViewCell, Void> { cell, indexPath, itemIdentifier in
+            cell.indicator.startAnimating()
+        }
+        let hashtagCell = UICollectionView.CellRegistration<TrendingHashtagCollectionViewCell, Hashtag> { cell, indexPath, hashtag in
             cell.updateUI(hashtag: hashtag)
         }
-        
+        let confirmLoadMoreCell = UICollectionView.CellRegistration<ConfirmLoadMoreCollectionViewCell, Bool> { [unowned self] cell, indexPath, isLoading in
+            cell.confirmLoadMore = self.confirmLoadMore
+            cell.isLoading = isLoading
+        }
         dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView) { (collectionView, indexPath, item) in
             switch item {
-            case let .tag(hashtag):
+            case .loadingIndicator:
-                return collectionView.dequeueConfiguredReusableCell(using: registration, for: indexPath, item: hashtag)
+                return collectionView.dequeueConfiguredReusableCell(using: loadingCell, for: indexPath, item: ())
+            case .tag(let hashtag):
+                return collectionView.dequeueConfiguredReusableCell(using: hashtagCell, for: indexPath, item: hashtag)
+            case .confirmLoadMore(let loading):
+                return collectionView.dequeueConfiguredReusableCell(using: confirmLoadMoreCell, for: indexPath, item: loading)
             }
         }
     }
@@ -58,18 +84,104 @@ class TrendingHashtagsViewController: UIViewController {
     override func viewWillAppear(_ animated: Bool) {
         super.viewWillAppear(animated)
         
-        let request = Client.getTrendingHashtags(limit: 10)
         Task {
-            guard let (hashtags, _) = try? await mastodonController.run(request) else {
+            await loadInitial()
-                return
-            }
-            var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
-            snapshot.appendSections([.trendingTags])
-            snapshot.appendItems(hashtags.map { .tag($0) })
-            await dataSource.apply(snapshot)
         }
     }
     
+    private func request(offset: Int?) -> Request<[Hashtag]> {
+        if mastodonController.instanceFeatures.hasMastodonVersion(3, 5, 0) {
+            return Client.getTrendingHashtags(offset: offset)
+        } else {
+            return Client.getTrendingHashtagsDeprecated(offset: offset)
+        }
+    }
+    
+    @MainActor
+    private func loadInitial() async {
+        guard case .unloaded = state else {
+            return
+        }
+        state = .loadingInitial
+        
+        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
+        snapshot.appendSections([.trendingTags])
+        snapshot.appendItems([.loadingIndicator])
+        await dataSource.apply(snapshot)
+        
+        do {
+            let request = self.request(offset: nil)
+            let (hashtags, _) = try await mastodonController.run(request)
+            snapshot.deleteItems([.loadingIndicator])
+            snapshot.appendItems(hashtags.map { .tag($0) })
+            state = .loaded
+            await dataSource.apply(snapshot)
+        } catch {
+            snapshot.deleteItems([.loadingIndicator])
+            await dataSource.apply(snapshot)
+            state = .unloaded
+            
+            let config = ToastConfiguration(from: error, with: "Error Loading Trending Tags", in: self) { [weak self] toast in
+                toast.dismissToast(animated: true)
+                await self?.loadInitial()
+            }
+            self.showToast(configuration: config, animated: true)
+        }
+    }
+    
+    @MainActor
+    private func loadOlder() async {
+        guard case .loaded = state else {
+            return
+        }
+        state = .loadingOlder
+        
+        let origSnapshot = dataSource.snapshot()
+        var snapshot = origSnapshot
+        if Preferences.shared.disableInfiniteScrolling {
+            snapshot.appendItems([.confirmLoadMore(false)])
+            await dataSource.apply(snapshot)
+            
+            for await _ in confirmLoadMore.values {
+                break
+            }
+            
+            snapshot.deleteItems([.confirmLoadMore(false)])
+            snapshot.appendItems([.confirmLoadMore(true)])
+            await dataSource.apply(snapshot, animatingDifferences: false)
+        } else {
+            snapshot.appendItems([.loadingIndicator])
+            await dataSource.apply(snapshot)
+        }
+        
+        do {
+            let request = self.request(offset: snapshot.itemIdentifiers.count - 1)
+            let (hashtags, _) = try await mastodonController.run(request)
+            var snapshot = origSnapshot
+            snapshot.appendItems(hashtags.map { .tag($0) })
+            await dataSource.apply(snapshot)
+        } catch {
+            await dataSource.apply(origSnapshot)
+            
+            let config = ToastConfiguration(from: error, with: "Error Loading Older Tags", in: self) { [weak self] toast in
+                toast.dismissToast(animated: true)
+                await self?.loadOlder()
+            }
+            self.showToast(configuration: config, animated: true)
+        }
+        
+        state = .loaded
+    }
+    
+}
+
+extension TrendingHashtagsViewController {
+    enum State {
+        case unloaded
+        case loadingInitial
+        case loaded
+        case loadingOlder
+    }
 }
 
 extension TrendingHashtagsViewController {
@@ -77,11 +189,45 @@ extension TrendingHashtagsViewController {
         case trendingTags
     }
     enum Item: Hashable {
+        case loadingIndicator
         case tag(Hashtag)
+        case confirmLoadMore(Bool)
+        
+        var hideSeparators: Bool {
+            switch self {
+            case .loadingIndicator:
+                return true
+            case .tag(_):
+                return false
+            case .confirmLoadMore(_):
+                return false
+            }
+        }
+        
+        var shouldSelect: Bool {
+            if case .tag(_) = self {
+                return true
+            } else {
+                return false
+            }
+        }
     }
 }
 
 extension TrendingHashtagsViewController: 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, shouldSelectItemAt indexPath: IndexPath) -> Bool {
+        return dataSource.itemIdentifier(for: indexPath)?.shouldSelect ?? false
+    }
+    
     func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
         guard let item = dataSource.itemIdentifier(for: indexPath),
               case let .tag(hashtag) = item else {

Tusker/Screens/Explore/TrendingLinksViewController.swift

@@ -132,8 +132,8 @@ class TrendingLinksViewController: UIViewController, CollectionViewController {
             snapshot.deleteSections([.loadingIndicator])
             snapshot.appendSections([.links])
             snapshot.appendItems(links.map { .link($0) })
-            await dataSource.apply(snapshot)
             state = .loaded
+            await dataSource.apply(snapshot)
         } catch {
             await dataSource.apply(NSDiffableDataSourceSnapshot())
             state = .unloaded