unified the filtering of the gallery items

ElementX/Sources/Screens/FilePreviewScreen/TimelineMediaPreviewDataSource.swift

@@ -449,12 +449,8 @@ private extension RoomTimelineItemViewState {
             return [TimelineMediaPreviewItem.Media(roomTimelineItemViewState: self)].compactMap { $0 }
         }
         
-        return galleryItem.content.items.filter { item in
-            guard let allowedItemType = item.allowedItemType else {
-                return false // Nothing to preview, and unlike a tile there's no index to line up with.
-            }
-            
-            return allowedGalleryItemTypes?.contains(allowedItemType) ?? true
-        }.map { TimelineMediaPreviewItem.Media(galleryParent: galleryItem, item: $0) }
+        return galleryItem.content.attachments(allowedTypes: allowedGalleryItemTypes).map {
+            TimelineMediaPreviewItem.Media(galleryParent: galleryItem, item: $0.item)
+        }
     }
 }

ElementX/Sources/Screens/MediaEventsTimelineScreen/MediaEventsTimelineScreenModels.swift

@@ -13,7 +13,7 @@ enum MediaEventsTimelineScreenViewModelAction {
     case viewInRoomTimeline(TimelineItemIdentifier)
 }
 
-nonisolated enum MediaEventsTimelineScreenMode {
+enum MediaEventsTimelineScreenMode {
     case media
     case files
 }

ElementX/Sources/Screens/MediaEventsTimelineScreen/MediaEventsTimelineScreenViewModel.swift

@@ -204,7 +204,7 @@ class MediaEventsTimelineScreenViewModel: MediaEventsTimelineScreenViewModelType
                 return [itemViewState]
             case .gallery(let galleryItem):
                 // A gallery's attachments are displayed flattened, listed individually.
-                let flattenedItems = galleryItem.itemsAsIndividualMessages(for: state.screenMode)
+                let flattenedItems = galleryItem.itemsAsIndividualMessages(allowedTypes: timelineViewState.allowedGalleryItemTypes)
                 for (mediaIndex, item) in flattenedItems {
                     newGalleryItemLookup[item.id.uniqueID] = .init(parentID: galleryItem.id, mediaIndex: mediaIndex)
                 }
@@ -285,32 +285,31 @@ class MediaEventsTimelineScreenViewModel: MediaEventsTimelineScreenViewModelType
 }
 
 private extension GalleryRoomTimelineItem {
-    /// Represents the gallery's attachments as though each had been sent as an individual message, so
-    /// that the screen can list them alongside the room's other media, keeping only those that belong
-    /// in the given mode. Each one keeps the gallery's event ID but is given its own unique ID so that
-    /// the attachments remain distinct within the list.
-    func itemsAsIndividualMessages(for screenMode: MediaEventsTimelineScreenMode) -> [(mediaIndex: Int, item: EventBasedMessageTimelineItemProtocol)] {
+    /// Represents the gallery's attachments of the given types as though each had been sent as an
+    /// individual message, so that the screen can list them alongside the room's other media. Each one
+    /// keeps the gallery's event ID but is given its own unique ID so that they remain distinct.
+    func itemsAsIndividualMessages(allowedTypes: [TimelineAllowedGalleryItemType]?) -> [(mediaIndex: Int, item: EventBasedMessageTimelineItemProtocol)] {
         guard let eventOrTransactionID = id.eventOrTransactionID else { return [] }
         
-        return content.items.enumerated().compactMap { mediaIndex, galleryItem in
+        return content.attachments(allowedTypes: allowedTypes).compactMap { mediaIndex, galleryItem in
             let itemID = TimelineItemIdentifier.event(uniqueID: .init("\(id.uniqueID.value)-\(mediaIndex)"),
                                                       eventOrTransactionID: eventOrTransactionID)
             
             let item: EventBasedMessageTimelineItemProtocol? = switch galleryItem {
-            case .image(_, let content) where screenMode == .media:
+            case .image(_, let content):
                 ImageRoomTimelineItem(id: itemID, timestamp: timestamp, isOutgoing: isOutgoing, isEditable: isEditable,
                                       canBeRepliedTo: canBeRepliedTo, sender: sender, content: content, properties: properties)
-            case .video(_, let content) where screenMode == .media:
+            case .video(_, let content):
                 VideoRoomTimelineItem(id: itemID, timestamp: timestamp, isOutgoing: isOutgoing, isEditable: isEditable,
                                       canBeRepliedTo: canBeRepliedTo, sender: sender, content: content, properties: properties)
-            case .audio(_, let content) where screenMode == .files:
+            case .audio(_, let content):
                 AudioRoomTimelineItem(id: itemID, timestamp: timestamp, isOutgoing: isOutgoing, isEditable: isEditable,
                                       canBeRepliedTo: canBeRepliedTo, sender: sender, content: content, properties: properties)
-            case .file(_, let content) where screenMode == .files:
+            case .file(_, let content):
                 FileRoomTimelineItem(id: itemID, timestamp: timestamp, isOutgoing: isOutgoing, isEditable: isEditable,
                                      canBeRepliedTo: canBeRepliedTo, sender: sender, content: content, properties: properties)
-            default:
-                nil // Attachments of an unknown type, or that belong in the other mode.
+            case .other:
+                nil // Filtered out above, as there's nothing to show for it.
             }
             
             guard let item else { return nil }

ElementX/Sources/Screens/MediaEventsTimelineScreen/View/MediaEventsTimelineScreen.swift

@@ -361,7 +361,15 @@ struct MediaEventsTimelineScreen_Previews: PreviewProvider, TestablePreview {
             timelineItems.append(contentsOf: [makeFileItem(url: .mockMXCScanning), makeFileItem(url: .mockMXCUnsafe)])
         }
         
-        return TimelineControllerMock(.init(timelineKind: .media(.mediaFilesScreen), timelineItems: timelineItems))
+        // Mirrors the message types that the flow coordinator filters each timeline to.
+        let allowedGalleryItemTypes: [TimelineAllowedGalleryItemType] = switch screenMode {
+        case .media: [.image, .video]
+        case .files: [.file, .audio]
+        }
+        
+        return TimelineControllerMock(.init(timelineKind: .media(.mediaFilesScreen),
+                                            timelineItems: timelineItems,
+                                            allowedGalleryItemTypes: allowedGalleryItemTypes))
     }
     
     private static func makeImageItem(url: URL) -> ImageRoomTimelineItem {

ElementX/Sources/Services/Timeline/TimelineItems/Items/Messages/GalleryRoomTimelineItemContent.swift

@@ -15,6 +15,21 @@ nonisolated struct GalleryRoomTimelineItemContent: Hashable {
     /// The original textual representation of the formatted caption directly from the event (usually HTML code)
     var formattedCaptionHTMLString: String?
     let items: [GalleryItem]
+    
+    /// The attachments of the given types, paired with their position in the gallery so that they remain
+    /// identifiable once separated from it. Attachments of an unknown type are never included as there's
+    /// nothing to show for them.
+    /// - Parameter allowedTypes: The types to include, or `nil` to include them all.
+    func attachments(allowedTypes: [TimelineAllowedGalleryItemType]?) -> [(mediaIndex: Int, item: GalleryItem)] {
+        items.enumerated().compactMap { mediaIndex, item in
+            guard let allowedItemType = item.allowedItemType,
+                  allowedTypes?.contains(allowedItemType) ?? true else {
+                return nil
+            }
+            
+            return (mediaIndex, item)
+        }
+    }
 }
 
 /// Identifies a single attachment within a gallery message.

UnitTests/Sources/MediaEventsTimelineScreenViewModelTests.swift

@@ -12,8 +12,8 @@ import Testing
 struct MediaEventsTimelineScreenViewModelTests {
     @Test
     func changingScreenModeSwitchesTimelines() {
-        let mediaTimelineViewModel = makeTimelineViewModel()
-        let filesTimelineViewModel = makeTimelineViewModel()
+        let mediaTimelineViewModel = makeTimelineViewModel(allowedGalleryItemTypes: [.image, .video])
+        let filesTimelineViewModel = makeTimelineViewModel(allowedGalleryItemTypes: [.file, .audio])
         
         let viewModel = MediaEventsTimelineScreenViewModel(mediaTimelineViewModel: mediaTimelineViewModel,
                                                            filesTimelineViewModel: filesTimelineViewModel,
@@ -45,10 +45,12 @@ struct MediaEventsTimelineScreenViewModelTests {
     
     // MARK: - Helpers
     
-    // Both timelines are given the same mixed chunk of items so that the mode based filtering is what's under test.
-    private func makeTimelineViewModel() -> TimelineViewModel {
+    // Both timelines are given the same mixed chunk of items, filtered as they are in the app, so that
+    // the filtering of the items is what's under test.
+    private func makeTimelineViewModel(allowedGalleryItemTypes: [TimelineAllowedGalleryItemType]) -> TimelineViewModel {
         let timelineController = TimelineControllerMock(.init(timelineKind: .media(.mediaFilesScreen),
-                                                              timelineItems: [TimelineFixtures.separator] + TimelineFixtures.mediaChunk))
+                                                              timelineItems: [TimelineFixtures.separator] + TimelineFixtures.mediaChunk,
+                                                              allowedGalleryItemTypes: allowedGalleryItemTypes))
         return TimelineViewModel.mock(timelineKind: .media(.mediaFilesScreen), timelineController: timelineController)
     }