Extract TimelineLikeDataSource into separate protocol

Tusker/Screens/Notifications/NotificationsCollectionViewController.swift

@@ -40,7 +40,7 @@ class NotificationsCollectionViewController: UIViewController, TimelineLikeColle
         
         super.init(nibName: nil, bundle: nil)
         
-        self.controller = TimelineLikeController(delegate: self, ownerType: String(describing: self))
+        self.controller = TimelineLikeController(delegate: self, dataSource: self, ownerType: String(describing: self))
         
         addKeyCommand(MenuController.refreshCommand(discoverabilityTitle: "Refresh Notifications"))
     }
@@ -387,8 +387,16 @@ extension NotificationsCollectionViewController {
     }
 }
 
-// MARK: TimelineLikeControllerDelegate
+// MARK: TimelineLikeCollectionViewController
 extension NotificationsCollectionViewController {
+    enum Error: TimelineLikeCollectionViewError {
+        case noNewer
+        case noOlder
+        case allCaughtUp
+    }
+}
+
+extension NotificationsCollectionViewController: TimelineLikeControllerDataSource {
     typealias TimelineItem = NotificationGroup
     
     private static let pageSize = 40
@@ -478,27 +486,6 @@ extension NotificationsCollectionViewController {
         return NotificationGroup.mergeGroups(first: newerGroups, second: existingGroups, only: self.groupTypes)
     }
     
-    func handlePrependItems(_ timelineItems: [NotificationGroup]) async {
-        let topItem = dataSource.snapshot().itemIdentifiers(inSection: .notifications).first
-        
-        // we always replace all, because new items are merged with existing ones
-        await handleReplaceAllItems(timelineItems)
-        
-        // preserve the scroll position
-        // todo: this won't work for cmd+r when not at top
-        if let topID = topItem?.group?.notifications.first?.id {
-            // the exact item may have changed, due to merging
-            let newTopGroup = timelineItems.first {
-                $0.notifications.contains {
-                    $0.id == topID
-                }
-            }!
-            if let newTopIndexPath = dataSource.indexPath(for: .group(newTopGroup, nil, nil)) {
-                collectionView.scrollToItem(at: newTopIndexPath, at: .top, animated: false)
-            }
-        }
-    }
-    
     func loadOlder() async throws -> [NotificationGroup] {
         guard let older else {
             throw Error.noOlder
@@ -523,16 +510,34 @@ extension NotificationsCollectionViewController {
         let existingGroups = dataSource.snapshot().itemIdentifiers(inSection: .notifications).compactMap(\.group)
         return NotificationGroup.mergeGroups(first: existingGroups, second: olderGroups, only: self.groupTypes)
     }
+}
+
+// MARK: TimelineLikeControllerDelegate
+extension NotificationsCollectionViewController {
+    func handlePrependItems(_ timelineItems: [NotificationGroup]) async {
+        let topItem = dataSource.snapshot().itemIdentifiers(inSection: .notifications).first
+        
+        // we always replace all, because new items are merged with existing ones
+        await handleReplaceAllItems(timelineItems)
+        
+        // preserve the scroll position
+        // todo: this won't work for cmd+r when not at top
+        if let topID = topItem?.group?.notifications.first?.id {
+            // the exact item may have changed, due to merging
+            let newTopGroup = timelineItems.first {
+                $0.notifications.contains {
+                    $0.id == topID
+                }
+            }!
+            if let newTopIndexPath = dataSource.indexPath(for: .group(newTopGroup, nil, nil)) {
+                collectionView.scrollToItem(at: newTopIndexPath, at: .top, animated: false)
+            }
+        }
+    }
     
     func handleAppendItems(_ timelineItems: [NotificationGroup]) async {
         await handleReplaceAllItems(timelineItems)
     }
-    
-    enum Error: TimelineLikeCollectionViewError {
-        case noNewer
-        case noOlder
-        case allCaughtUp
-    }
 }
 
 extension NotificationsCollectionViewController: UICollectionViewDelegate {

Tusker/Screens/Profile/ProfileStatusesViewController.swift

@@ -45,7 +45,7 @@ class ProfileStatusesViewController: UIViewController, TimelineLikeCollectionVie
         
         super.init(nibName: nil, bundle: nil)
         
-        self.controller = TimelineLikeController(delegate: self, ownerType: String(describing: self))
+        self.controller = TimelineLikeController(delegate: self, dataSource: self, ownerType: String(describing: self))
         
         addKeyCommand(MenuController.refreshCommand(discoverabilityTitle: "Refresh Profile"))
     }
@@ -501,7 +501,16 @@ extension ProfileStatusesViewController {
     }
 }
 
-extension ProfileStatusesViewController: TimelineLikeControllerDelegate {
+// MARK: TimelineLikeCollectionViewController
+extension ProfileStatusesViewController {
+    enum Error: TimelineLikeCollectionViewError {
+        case noNewer
+        case noOlder
+        case allCaughtUp
+    }
+}
+
+extension ProfileStatusesViewController: TimelineLikeControllerDataSource {
     typealias TimelineItem = String // status ID
     
     private func request(for range: RequestRange = .default) -> Request<[Status]> {
@@ -572,12 +581,6 @@ extension ProfileStatusesViewController: TimelineLikeControllerDelegate {
             }
         }
     }
-    
-    enum Error: TimelineLikeCollectionViewError {
-        case noNewer
-        case noOlder
-        case allCaughtUp
-    }
 }
 
 extension ProfileStatusesViewController: UICollectionViewDelegate {

Tusker/Screens/Timeline/TimelineViewController.swift

@@ -66,7 +66,7 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
         
         super.init(nibName: nil, bundle: nil)
         
-        self.controller = TimelineLikeController(delegate: self, ownerType: String(describing: self))
+        self.controller = TimelineLikeController(delegate: self, dataSource: self, ownerType: String(describing: self))
                 
         self.navigationItem.title = timeline.title
         addKeyCommand(MenuController.refreshCommand(discoverabilityTitle: "Refresh Timeline"))
@@ -1092,8 +1092,18 @@ extension TimelineViewController {
     }
 }
 
-// MARK: TimelineLikeControllerDelegate
+// MARK: TimelineLikeCollectionViewController
 extension TimelineViewController {
+    enum Error: TimelineLikeCollectionViewError {
+        case noClient
+        case noNewer
+        case noOlder
+        case allCaughtUp
+        case noGap
+    }
+}
+
+extension TimelineViewController: TimelineLikeControllerDataSource {
     typealias TimelineItem = String // status ID
     
     // the maximum mastodon will provide in a single request
@@ -1209,7 +1219,10 @@ extension TimelineViewController {
         }
         self.showToast(configuration: config, animated: true)
     }
-    
+}
+
+// MARK: TimelineLikeControllerDelegate
+extension TimelineViewController {
     func handleFillGap(_ timelineItems: [String], direction: TimelineGapDirection) async {
         var snapshot = dataSource.snapshot()
         let addedItems: Bool
@@ -1297,14 +1310,6 @@ extension TimelineViewController {
             showToast(configuration: config, animated: true)
         }
     }
-    
-    enum Error: TimelineLikeCollectionViewError {
-        case noClient
-        case noNewer
-        case noOlder
-        case allCaughtUp
-        case noGap
-    }
 }
 
 extension TimelineViewController: UICollectionViewDelegate {

Tusker/TimelineLikeController.swift

@@ -10,20 +10,20 @@ import Foundation
 import OSLog
 import Combine
 
+protocol TimelineLikeControllerDataSource<TimelineItem>: AnyObject {
+    associatedtype TimelineItem: Sendable
+
+    func loadInitial() async throws -> [TimelineItem]
+    func loadNewer() async throws -> [TimelineItem]
+    func canLoadOlder() async -> Bool
+    func loadOlder() async throws -> [TimelineItem]
+    func loadGap(in direction: TimelineGapDirection) async throws -> [TimelineItem]
+}
+
 @MainActor
 protocol TimelineLikeControllerDelegate<TimelineItem>: AnyObject {
     associatedtype TimelineItem: Sendable
     
-    func loadInitial() async throws -> [TimelineItem]
-    
-    func loadNewer() async throws -> [TimelineItem]
-    
-    func canLoadOlder() async -> Bool
-    
-    func loadOlder() async throws -> [TimelineItem]
-    
-    func loadGap(in direction: TimelineGapDirection) async throws -> [TimelineItem]
-    
     func handleAddLoadingIndicator() async
     func handleRemoveLoadingIndicator() async
     func handleLoadAllError(_ error: Swift.Error) async
@@ -42,6 +42,7 @@ private let logger = Logger(subsystem: Bundle.main.bundleIdentifier!, category:
 class TimelineLikeController<Item: Sendable> {
     
     private unowned var delegate: any TimelineLikeControllerDelegate<Item>
+    private unowned var dataSource: any TimelineLikeControllerDataSource<Item>
     private let ownerType: String
     
     @AsyncObservable private(set) var state = State.notLoadedInitial {
@@ -54,8 +55,9 @@ class TimelineLikeController<Item: Sendable> {
         }
     }
     
-    init(delegate: any TimelineLikeControllerDelegate<Item>, ownerType: String) {
+    init(delegate: any TimelineLikeControllerDelegate<Item>, dataSource: any TimelineLikeControllerDataSource<Item>, ownerType: String) {
         self.delegate = delegate
+        self.dataSource = dataSource
         self.ownerType = ownerType
     }
     
@@ -81,7 +83,7 @@ class TimelineLikeController<Item: Sendable> {
         await emit(event: .addLoadingIndicator)
         state = .loadingInitial(token, hasAddedLoadingIndicator: true)
         do {
-            let items = try await delegate.loadInitial()
+            let items = try await dataSource.loadInitial()
             guard case .loadingInitial(token, _) = state else {
                 return
             }
@@ -118,7 +120,7 @@ class TimelineLikeController<Item: Sendable> {
         let token = LoadAttemptToken()
         state = .loadingNewer(token)
         do {
-            let items = try await delegate.loadNewer()
+            let items = try await dataSource.loadNewer()
             guard case .loadingNewer(token) = state else {
                 return
             }
@@ -137,7 +139,7 @@ class TimelineLikeController<Item: Sendable> {
             return
         }
         let token = LoadAttemptToken()
-        guard await delegate.canLoadOlder(),
+        guard await dataSource.canLoadOlder(),
               // Make sure we're still in the idle state before continuing on, since that may have chnaged while waiting for user input.
               // If the load more cell appears, then the users scrolls up and back down, the VC may kick off a second loadOlder task
               // but we only want one to proceed. The actor prevents a data race, and this prevents multiple simultaneousl loadOlder tasks from running.
@@ -148,7 +150,7 @@ class TimelineLikeController<Item: Sendable> {
         await emit(event: .addLoadingIndicator)
         state = .loadingOlder(token, hasAddedLoadingIndicator: true)
         do {
-            let items = try await delegate.loadOlder()
+            let items = try await dataSource.loadOlder()
             guard case .loadingOlder(token, _) = state else {
                 return
             }
@@ -171,7 +173,7 @@ class TimelineLikeController<Item: Sendable> {
         let token = LoadAttemptToken()
         state = .loadingGap(token, direction)
         do {
-            let items = try await delegate.loadGap(in: direction)
+            let items = try await dataSource.loadGap(in: direction)
             guard case .loadingGap(token, direction) = state else {
                 return
             }