Merge pull request #731 from vector-im/feature/fga/timeline_back_pagination

Feature/fga/timeline back pagination

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

@@ -59,21 +59,16 @@ class TimelinePresenter @Inject constructor(
         var lastReadMarkerIndex by rememberSaveable { mutableStateOf(Int.MAX_VALUE) }
         var lastReadMarkerId by rememberSaveable { mutableStateOf<EventId?>(null) }
 
-        val timelineItems = timelineItemsFactory
-            .flow()
-            .collectAsState()
-
-        val paginationState = timeline
-            .paginationState()
-            .collectAsState()
+        val timelineItems by timelineItemsFactory.collectItemsAsState()
+        val paginationState by timeline.paginationState.collectAsState()
 
         fun handleEvents(event: TimelineEvents) {
             when (event) {
-                TimelineEvents.LoadMore -> localCoroutineScope.loadMore(paginationState.value)
+                TimelineEvents.LoadMore -> localCoroutineScope.loadMore(paginationState)
                 is TimelineEvents.SetHighlightedEvent -> highlightedEventId.value = event.eventId
                 is TimelineEvents.OnScrollFinished -> {
                     // Get last valid EventId seen by the user, as the first index might refer to a Virtual item
-                    val eventId = getLastEventIdBeforeOrAt(event.firstIndex, timelineItems.value) ?: return
+                    val eventId = getLastEventIdBeforeOrAt(event.firstIndex, timelineItems) ?: return
                     if (event.firstIndex <= lastReadMarkerIndex && eventId != lastReadMarkerId) {
                         lastReadMarkerIndex = event.firstIndex
                         lastReadMarkerId = eventId
@@ -85,11 +80,11 @@ class TimelinePresenter @Inject constructor(
 
         LaunchedEffect(Unit) {
             timeline
-                .timelineItems()
+                .timelineItems
                 .onEach(timelineItemsFactory::replaceWith)
                 .onEach { timelineItems ->
                     if (timelineItems.isEmpty()) {
-                        loadMore(paginationState.value)
+                        loadMore(paginationState)
                     }
                 }
                 .launchIn(this)
@@ -97,8 +92,8 @@ class TimelinePresenter @Inject constructor(
 
         return TimelineState(
             highlightedEventId = highlightedEventId.value,
-            paginationState = paginationState.value,
-            timelineItems = timelineItems.value,
+            paginationState = paginationState,
+            timelineItems = timelineItems,
             eventSink = ::handleEvents
         )
     }

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

@@ -39,7 +39,6 @@ import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.saveable.rememberSaveable
-import androidx.compose.runtime.snapshotFlow
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.res.pluralStringResource
@@ -62,7 +61,6 @@ import io.element.android.libraries.designsystem.theme.components.Icon
 import io.element.android.libraries.matrix.api.core.EventId
 import io.element.android.libraries.matrix.api.core.UserId
 import kotlinx.collections.immutable.ImmutableList
-import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.launch
 
 @Composable
@@ -123,8 +121,7 @@ fun TimelineView(
 
         TimelineScrollHelper(
             lazyListState = lazyListState,
-            timelineItems = state.timelineItems,
-            onLoadMore = ::onReachedLoadMore
+            timelineItems = state.timelineItems
         )
     }
 }
@@ -222,7 +219,6 @@ fun TimelineItemRow(
 internal fun BoxScope.TimelineScrollHelper(
     lazyListState: LazyListState,
     timelineItems: ImmutableList<TimelineItem>,
-    onLoadMore: () -> Unit = {},
 ) {
     val coroutineScope = rememberCoroutineScope()
     val firstVisibleItemIndex by remember { derivedStateOf { lazyListState.firstVisibleItemIndex } }
@@ -236,24 +232,6 @@ internal fun BoxScope.TimelineScrollHelper(
         }
     }
 
-    // Handle load more preloading
-    val loadMore by remember {
-        derivedStateOf {
-            val layoutInfo = lazyListState.layoutInfo
-            val totalItemsNumber = layoutInfo.totalItemsCount
-            val lastVisibleItemIndex = (layoutInfo.visibleItemsInfo.lastOrNull()?.index ?: 0) + 1
-            lastVisibleItemIndex > (totalItemsNumber - 30)
-        }
-    }
-
-    LaunchedEffect(loadMore) {
-        snapshotFlow { loadMore }
-            .distinctUntilChanged()
-            .collect {
-                onLoadMore()
-            }
-    }
-
     // Jump to bottom button
     if (firstVisibleItemIndex > 2) {
         FloatingActionButton(

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

@@ -16,6 +16,9 @@
 
 package io.element.android.features.messages.impl.timeline.factories
 
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.State
+import androidx.compose.runtime.collectAsState
 import androidx.recyclerview.widget.DiffUtil
 import io.element.android.features.messages.impl.timeline.diff.CacheInvalidator
 import io.element.android.features.messages.impl.timeline.diff.MatrixTimelineItemsDiffCallback
@@ -27,11 +30,8 @@ import io.element.android.libraries.core.coroutine.CoroutineDispatchers
 import io.element.android.libraries.matrix.api.timeline.MatrixTimelineItem
 import kotlinx.collections.immutable.ImmutableList
 import kotlinx.collections.immutable.persistentListOf
-import kotlinx.collections.immutable.toImmutableList
 import kotlinx.collections.immutable.toPersistentList
 import kotlinx.coroutines.flow.MutableStateFlow
-import kotlinx.coroutines.flow.StateFlow
-import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
@@ -55,7 +55,10 @@ class TimelineItemsFactory @Inject constructor(
     private val lock = Mutex()
     private val cacheInvalidator = CacheInvalidator(timelineItemsCache)
 
-    fun flow(): StateFlow<ImmutableList<TimelineItem>> = timelineItems.asStateFlow()
+    @Composable
+    fun collectItemsAsState(): State<ImmutableList<TimelineItem>> {
+        return timelineItems.collectAsState()
+    }
 
     suspend fun replaceWith(
         timelineItems: List<MatrixTimelineItem>,