Fix loading initial items of non-live timelines (#6598)

This was done automatically by the SDK in the past by returning a `Reset` timeline update, but this behaviour changed and now we have to do it.

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/timeline/TimelineView.kt

@@ -84,6 +84,7 @@ import kotlinx.coroutines.flow.collectLatest
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.conflate
 import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.transform
 import kotlinx.coroutines.launch
 import timber.log.Timber
@@ -262,11 +263,16 @@ private fun TimelinePrefetchingHelper(
             firstVisibleItemIndex + layoutInfo.visibleItemsInfo.size >= layoutInfo.totalItemsCount - 40
         }
 
+        // If we have no timeline items, we need to back paginate to load some messages. This usually happens on all timelines except for live ones.
+        // This automatic pagination was previously done by the SDK, and we received a `Reset` update, but now we need to do it ourselves.
+        val isEmptyTimelineFlow = layoutInfoFlow.map { it.totalItemsCount == 0 }
+
         combine(
             isCloseToStartOfLoadedTimelineFlow.distinctUntilChanged(),
             isScrollingFlow.distinctUntilChanged(),
-        ) { needsPrefetch, isScrolling ->
+            isEmptyTimelineFlow,
-            needsPrefetch && isScrolling
+        ) { needsPrefetch, isScrolling, isEmptyAndNeedsBackPagination ->
+            isEmptyAndNeedsBackPagination || needsPrefetch && isScrolling
         }
             .distinctUntilChanged()
             .collectLatest { needsPrefetch ->

features/messages/impl/src/test/kotlin/io/element/android/features/messages/impl/MessagesViewTest.kt

@@ -522,6 +522,9 @@ class MessagesViewTest {
         rule.setMessagesView(
             state = stateWithActionListState,
         )
+        // Clear initial 'LoadMore' event emitted when setting the state
+        eventsRecorder.clear()
+
         val verifiedUserSendFailure = rule.activity.getString(CommonStrings.screen_timeline_item_menu_send_failure_changed_identity, "Alice")
         rule.onNodeWithText(verifiedUserSendFailure).performClick()
         // Give time for the close animation to complete
@@ -585,6 +588,9 @@ class MessagesViewTest {
             ),
         )
         rule.setMessagesView(state = state)
+        // Clear initial 'LoadMore' event emitted when setting the state
+        eventsRecorder.clear()
+
         rule.onNodeWithText("This is a pinned message").performClick()
         eventsRecorder.assertSingle(TimelineEvent.FocusOnEvent(AN_EVENT_ID, debounce = FOCUS_ON_PINNED_EVENT_DEBOUNCE_DURATION_IN_MILLIS.milliseconds))
     }
@@ -601,6 +607,9 @@ class MessagesViewTest {
             timelineState = aTimelineState(eventSink = eventsRecorder)
         )
         rule.setMessagesView(state = state)
+        // Clear initial 'LoadMore' event emitted when setting the state
+        eventsRecorder.clear()
+
         val text = rule.activity.getString(R.string.screen_room_timeline_tombstoned_room_action)
         // The bottomsheet subcompose seems to make the node to appear twice
         rule.onAllNodesWithText(text).onFirst().performClick()

features/messages/impl/src/test/kotlin/io/element/android/features/messages/impl/timeline/TimelineViewTest.kt

@@ -67,24 +67,31 @@ class TimelineViewTest {
 
     @Test
     fun `reaching the end of the timeline does not send a LoadMore event`() {
-        val eventsRecorder = EventsRecorder<TimelineEvent>(expectEvents = false)
+        val eventsRecorder = EventsRecorder<TimelineEvent>()
         rule.setTimelineView(
             state = aTimelineState(
+                timelineItems = persistentListOf(aTimelineItemEvent(content = aTimelineItemImageContent())),
                 eventSink = eventsRecorder,
             ),
         )
+        eventsRecorder.assertSingle(TimelineEvent.OnScrollFinished(firstIndex = 0))
     }
 
     @Test
     fun `scroll to bottom on live timeline does not emit the Event`() {
-        val eventsRecorder = EventsRecorder<TimelineEvent>(expectEvents = false)
+        val eventsRecorder = EventsRecorder<TimelineEvent>()
         rule.setTimelineView(
             state = aTimelineState(
+                timelineItems = persistentListOf(aTimelineItemEvent(content = aTimelineItemImageContent())),
                 isLive = true,
                 eventSink = eventsRecorder,
             ),
             forceJumpToBottomVisibility = true,
         )
+
+        eventsRecorder.assertSingle(TimelineEvent.OnScrollFinished(firstIndex = 0))
+        eventsRecorder.clear()
+
         val contentDescription = rule.activity.getString(CommonStrings.a11y_jump_to_bottom)
         rule.onNodeWithContentDescription(contentDescription).performClick()
     }
@@ -94,15 +101,33 @@ class TimelineViewTest {
         val eventsRecorder = EventsRecorder<TimelineEvent>()
         rule.setTimelineView(
             state = aTimelineState(
+                timelineItems = persistentListOf(aTimelineItemEvent(content = aTimelineItemImageContent())),
                 isLive = false,
                 eventSink = eventsRecorder,
             ),
         )
+
+        eventsRecorder.assertSingle(TimelineEvent.OnScrollFinished(firstIndex = 0))
+        eventsRecorder.clear()
+
         val contentDescription = rule.activity.getString(CommonStrings.a11y_jump_to_bottom)
         rule.onNodeWithContentDescription(contentDescription).performClick()
         eventsRecorder.assertSingle(TimelineEvent.JumpToLive)
     }
 
+    @Test
+    fun `an empty timeline triggers a prefetch`() {
+        val eventsRecorder = EventsRecorder<TimelineEvent>()
+        rule.setTimelineView(
+            state = aTimelineState(
+                timelineItems = persistentListOf(),
+                eventSink = eventsRecorder,
+            ),
+        )
+
+        eventsRecorder.assertSingle(TimelineEvent.LoadMore(Timeline.PaginationDirection.BACKWARDS))
+    }
+
     @Test
     fun `show shield dialog`() {
         val eventsRecorder = EventsRecorder<TimelineEvent>()
@@ -133,11 +158,15 @@ class TimelineViewTest {
         val eventsRecorder = EventsRecorder<TimelineEvent>()
         rule.setTimelineView(
             state = aTimelineState(
+                timelineItems = persistentListOf(aTimelineItemEvent(content = aTimelineItemImageContent())),
                 isLive = false,
                 eventSink = eventsRecorder,
                 messageShield = aCriticalShield(),
             ),
         )
+        eventsRecorder.assertSingle(TimelineEvent.OnScrollFinished(firstIndex = 0))
+        eventsRecorder.clear()
+
         rule.clickOn(CommonStrings.action_ok)
         eventsRecorder.assertSingle(TimelineEvent.HideShieldDialog)
     }