Open a full-screen preview when tapping a gallery item

Tapping a gallery tile/row opens the existing media preview scoped to that gallery's attachments, paging between them. Introduces a typed MediaPreviewItemID (replacing the stringly-typed preview identifier) and a gallery-scoped TimelineMediaPreviewDataSource; the tap routes through TimelineInteractionHandler/TimelineViewModel. Non-previewable (.other) items are skipped without shifting the tapped index.

Co-authored-by: svetoslav.mitov <svetoslav.mitov@sportinno.com>

just use id instead of previewID

removed horrible multiline ternary

pr suggestions

remove redundant code

remove empty caption display + gallery uses the appropriate media timeline actions

ElementX/Sources/Screens/Timeline/TimelineInteractionHandler.swift

@@ -239,6 +239,10 @@ class TimelineInteractionHandler {
             text = content.caption ?? ""
             htmlText = content.formattedCaptionHTMLString
             editType = text.isEmpty ? .addCaption : .editCaption
+        case .gallery(let content):
+            text = content.caption ?? ""
+            htmlText = content.formattedCaptionHTMLString
+            editType = text.isEmpty ? .addCaption : .editCaption
         default:
             text = messageTimelineItem.body
         }
@@ -569,6 +573,16 @@ class TimelineInteractionHandler {
         }
     }
     
+    /// Opens a media preview scoped to a single gallery's attachments. The preview pages
+    /// only between the items of that one gallery — siblings in the wider timeline aren't
+    /// reachable from this entry point (use the regular media tap for that).
+    func processGalleryItemTap(itemID: TimelineItemIdentifier, index: Int) -> TimelineControllerAction {
+        guard let galleryItem = timelineController.timelineItems.firstUsingStableID(itemID) as? GalleryRoomTimelineItem else {
+            return .none
+        }
+        return .displayGalleryPreview(galleryItem: galleryItem, initialIndex: index)
+    }
+    
     // MARK: - Private
     
     private func buildReplyInfo(for item: EventBasedTimelineItemProtocol) -> ReplyInfo {

ElementX/Sources/Screens/Timeline/TimelineModels.swift

@@ -53,6 +53,7 @@ enum TimelineViewAction {
     case itemDisappeared(itemID: TimelineItemIdentifier)
     
     case mediaTapped(itemID: TimelineItemIdentifier)
+    case galleryItemTapped(itemID: TimelineItemIdentifier, index: Int)
     case itemSendInfoTapped(itemID: TimelineItemIdentifier)
     case toggleReaction(key: String, itemID: TimelineItemIdentifier)
     case sendReadReceiptIfNeeded(TimelineItemIdentifier)

ElementX/Sources/Screens/Timeline/TimelineViewModel.swift

@@ -159,6 +159,8 @@ class TimelineViewModel: TimelineViewModelType, TimelineViewModelProtocol {
             Task { await timelineController.processItemDisappearance(id) }
         case .mediaTapped(let id):
             Task { await handleMediaTapped(with: id) }
+        case .galleryItemTapped(let id, let index):
+            handleGalleryItemTapped(itemID: id, index: index)
         case .itemSendInfoTapped(let itemID):
             handleItemSendInfoTapped(itemID: itemID)
         case .toggleReaction(let emoji, let itemID):
@@ -708,6 +710,8 @@ class TimelineViewModel: TimelineViewModelType, TimelineViewModelProtocol {
             
             let mediaPreviewViewModel = makeMediaPreviewViewModel(item: item, timelineViewModelKind: timelineViewModelKind)
             actionsSubject.send(.displayMediaPreview(mediaPreviewViewModel))
+        case .displayGalleryPreview:
+            fatalError("Galleries open through the dedicated galleryItemTapped path, which carries the tapped index.")
         case .displayLocation(let location):
             actionsSubject.send(.displayLocation(location))
         case .displayLiveLocation(let sender, let initialLiveLocationShare):
@@ -718,6 +722,18 @@ class TimelineViewModel: TimelineViewModelType, TimelineViewModelProtocol {
         state.showLoading = false
     }
     
+    private func handleGalleryItemTapped(itemID: TimelineItemIdentifier, index: Int) {
+        if case let .displayGalleryPreview(galleryItem, initialIndex) = timelineInteractionHandler.processGalleryItemTap(itemID: itemID, index: index) {
+            displayGalleryPreview(galleryItem: galleryItem, initialIndex: initialIndex)
+        }
+    }
+    
+    private func displayGalleryPreview(galleryItem: GalleryRoomTimelineItem, initialIndex: Int) {
+        actionsSubject.send(.composer(action: .removeFocus))
+        let mediaPreviewViewModel = makeGalleryPreviewViewModel(galleryItem: galleryItem, initialIndex: initialIndex)
+        actionsSubject.send(.displayMediaPreview(mediaPreviewViewModel))
+    }
+    
     private func handleItemSendInfoTapped(itemID: TimelineItemIdentifier) {
         guard let timelineItem = timelineController.timelineItems.firstUsingStableID(itemID) else {
             MXLog.warning("Couldn't find timeline item.")
@@ -833,6 +849,17 @@ class TimelineViewModel: TimelineViewModelType, TimelineViewModelProtocol {
                                              appMediator: appMediator)
     }
     
+    private func makeGalleryPreviewViewModel(galleryItem: GalleryRoomTimelineItem,
+                                             initialIndex: Int) -> TimelineMediaPreviewViewModel {
+        TimelineMediaPreviewViewModel(galleryItem: galleryItem,
+                                      initialIndex: initialIndex,
+                                      timelineViewModel: self,
+                                      mediaProvider: userSession.mediaProvider,
+                                      photoLibraryManager: PhotoLibraryManager(),
+                                      userIndicatorController: userIndicatorController,
+                                      appMediator: appMediator)
+    }
+    
     // MARK: - Timeline Item Building
     
     private func buildTimelineViews(timelineItems: [RoomTimelineItemProtocol], isSwitchingTimelines: Bool = false) {

ElementX/Sources/Screens/Timeline/View/TimelineItemViews/GalleryItemTileView.swift

@@ -107,6 +107,7 @@ struct GalleryItemTileView: View {
                 .font(.compound.headingSMSemibold)
                 .foregroundStyle(.compound.textPrimary)
         }
+        .allowsHitTesting(false) // Let the tap fall through to the tile below.
     }
     
     private func formatted(duration: TimeInterval) -> String {

ElementX/Sources/Screens/Timeline/View/TimelineItemViews/GalleryRoomTimelineView.swift

@@ -27,15 +27,13 @@ struct GalleryRoomTimelineView: View {
                 if usesListLayout {
                     GalleryListView(items: timelineItem.content.items,
                                     mediaProvider: context?.mediaProvider,
-                                    contentScannerService: context?.contentScannerService) { _ in
-                        // Tapping to open the full-screen preview lands in a follow-up.
-                    }
+                                    contentScannerService: context?.contentScannerService,
+                                    onItemTap: tap)
                 } else {
                     GalleryGridView(items: timelineItem.content.items,
                                     mediaProvider: context?.mediaProvider,
-                                    contentScannerService: context?.contentScannerService) { _ in
-                        // Tapping to open the full-screen preview lands in a follow-up.
-                    }
+                                    contentScannerService: context?.contentScannerService,
+                                    onItemTap: tap)
                 }
                 
                 if hasMediaCaption {
@@ -61,6 +59,10 @@ struct GalleryRoomTimelineView: View {
                               boostFontSize: timelineItem.shouldBoost)
         }
     }
+    
+    private func tap(index: Int) {
+        context?.send(viewAction: .galleryItemTapped(itemID: timelineItem.id, index: index))
+    }
 }
 
 // MARK: - Previews