Implement permalink support for /relations live thread timeline

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/timeline/DefaultTimeline.kt

@@ -301,7 +301,13 @@ internal class DefaultTimeline(private val roomId: String,
         Timber.v("Post snapshot of ${snapshot.size} events")
         withContext(coroutineDispatchers.main) {
             listeners.forEach {
-                tryOrNull { it.onTimelineUpdated(snapshot) }
+                if (initialEventId != null && isFromThreadTimeline && snapshot.firstOrNull { it.eventId == initialEventId } == null) {
+                    // We are in a thread timeline with a permalink, post update timeline only when the appropriate message have been found
+                    tryOrNull { it.onTimelineUpdated(arrayListOf()) }
+                } else {
+                    // In all the other cases update timeline as expected
+                    tryOrNull { it.onTimelineUpdated(snapshot) }
+                }
             }
         }
     }

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/timeline/TimelineChunk.kt

@@ -171,11 +171,12 @@ internal class TimelineChunk(private val chunkEntity: ChunkEntity,
      * always fetch results, while we want our data to be up to dated.
      */
     suspend fun loadMoreThread(count: Int, direction: Timeline.Direction): LoadMoreResult {
+        val rootThreadEventId = timelineSettings.rootThreadEventId ?: return LoadMoreResult.FAILURE
         return if (direction == Timeline.Direction.BACKWARDS) {
             try {
                 fetchThreadTimelineTask.execute(FetchThreadTimelineTask.Params(
                         roomId,
-                        timelineSettings.rootThreadEventId!!,
+                        rootThreadEventId,
                         chunkEntity.prevToken,
                         count
                 )).toLoadMoreResult()

vector/src/main/java/im/vector/app/features/home/room/detail/TimelineViewModel.kt

@@ -156,6 +156,9 @@ class TimelineViewModel @AssistedInject constructor(
 
     companion object : MavericksViewModelFactory<TimelineViewModel, RoomDetailViewState> by hiltMavericksViewModelFactory() {
         const val PAGINATION_COUNT = 50
+        // The larger the number the faster the results, COUNT=200 for 500 thread messages its x4 faster than COUNT=50
+        const val PAGINATION_COUNT_THREADS_PERMALINK = 200
+
     }
 
     init {
@@ -1174,10 +1177,30 @@ class TimelineViewModel @AssistedInject constructor(
         }
     }
 
+    /**
+     * Navigates to the appropriate event (by paginating the thread timeline until the event is found
+     * in the snapshot. The main reason for this function is to support the /relations api
+     */
+    private var threadPermalinkHandled = false
+    private fun navigateToThreadEventIfNeeded(snapshot: List<TimelineEvent>) {
+        if (eventId != null && initialState.rootThreadEventId != null) {
+            // When we have a permalink and we are in a thread timeline
+            if (snapshot.firstOrNull { it.eventId == eventId } != null && !threadPermalinkHandled) {
+                // Permalink event found lets navigate there
+                handleNavigateToEvent(RoomDetailAction.NavigateToEvent(eventId, true))
+                threadPermalinkHandled = true
+            } else {
+                // Permalink event not found yet continue paginating
+                timeline.paginate(Timeline.Direction.BACKWARDS, PAGINATION_COUNT_THREADS_PERMALINK)
+            }
+        }
+    }
+
     override fun onTimelineUpdated(snapshot: List<TimelineEvent>) {
         viewModelScope.launch {
             // tryEmit doesn't work with SharedFlow without cache
             timelineEvents.emit(snapshot)
+            navigateToThreadEventIfNeeded(snapshot)
         }
     }