Subscribe to RoomListItems in the visible range (#3169)

* Subscribe to `RoomListItems` in the visible range

This ensures the room list items always have updated info.

features/roomlist/impl/src/main/kotlin/io/element/android/features/roomlist/impl/RoomListEvents.kt

@@ -20,6 +20,7 @@ import io.element.android.features.roomlist.impl.model.RoomListRoomSummary
 import io.element.android.libraries.matrix.api.core.RoomId
 
 sealed interface RoomListEvents {
+    data class UpdateVisibleRange(val range: IntRange) : RoomListEvents
     data object DismissRequestVerificationPrompt : RoomListEvents
     data object DismissRecoveryKeyPrompt : RoomListEvents
     data object ToggleSearchResults : RoomListEvents

features/roomlist/impl/src/main/kotlin/io/element/android/features/roomlist/impl/RoomListPresenter.kt

@@ -68,6 +68,8 @@ import io.element.android.services.analyticsproviders.api.trackers.captureIntera
 import kotlinx.collections.immutable.toPersistentList
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.flow.collect
 import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.first
@@ -78,6 +80,8 @@ import kotlinx.coroutines.flow.takeWhile
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
+private const val EXTENDED_RANGE_SIZE = 40
+
 class RoomListPresenter @Inject constructor(
     private val client: MatrixClient,
     private val networkMonitor: NetworkMonitor,
@@ -122,6 +126,9 @@ class RoomListPresenter @Inject constructor(
 
         fun handleEvents(event: RoomListEvents) {
             when (event) {
+                is RoomListEvents.UpdateVisibleRange -> coroutineScope.launch {
+                    updateVisibleRange(event.range)
+                }
                 RoomListEvents.DismissRequestVerificationPrompt -> securityBannerDismissed = true
                 RoomListEvents.DismissRecoveryKeyPrompt -> securityBannerDismissed = true
                 RoomListEvents.ToggleSearchResults -> searchState.eventSink(RoomListSearchEvents.ToggleSearchVisibility)
@@ -283,6 +290,22 @@ class RoomListPresenter @Inject constructor(
                 }
         }
     }
+
+    private var currentUpdateVisibleRangeJob: Job? = null
+    private fun CoroutineScope.updateVisibleRange(range: IntRange) {
+        currentUpdateVisibleRangeJob?.cancel()
+        currentUpdateVisibleRangeJob = launch(SupervisorJob()) {
+            if (range.isEmpty()) return@launch
+            val currentRoomList = roomListDataSource.allRooms.first()
+            // Use extended range to 'prefetch' the next rooms info
+            val midExtendedRangeSize = EXTENDED_RANGE_SIZE / 2
+            val extendedRange = range.first until range.last + midExtendedRangeSize
+            val roomIds = extendedRange.mapNotNull { index ->
+                currentRoomList.getOrNull(index)?.roomId
+            }
+            roomListDataSource.subscribeToVisibleRooms(roomIds)
+        }
+    }
 }
 
 @VisibleForTesting

features/roomlist/impl/src/main/kotlin/io/element/android/features/roomlist/impl/components/RoomListContentView.kt

@@ -30,6 +30,11 @@ import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.itemsIndexed
 import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.derivedStateOf
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberUpdatedState
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.res.stringResource
@@ -165,6 +170,18 @@ private fun RoomsViewList(
     modifier: Modifier = Modifier,
 ) {
     val lazyListState = rememberLazyListState()
+    val visibleRange by remember {
+        derivedStateOf {
+            val layoutInfo = lazyListState.layoutInfo
+            val firstItemIndex = layoutInfo.visibleItemsInfo.firstOrNull()?.index ?: 0
+            val size = layoutInfo.visibleItemsInfo.size
+            firstItemIndex until firstItemIndex + size
+        }
+    }
+    val updatedEventSink by rememberUpdatedState(newValue = eventSink)
+    LaunchedEffect(visibleRange) {
+        updatedEventSink(RoomListEvents.UpdateVisibleRange(visibleRange))
+    }
     LazyColumn(
         state = lazyListState,
         modifier = modifier,
@@ -177,7 +194,7 @@ private fun RoomsViewList(
                     item {
                         ConfirmRecoveryKeyBanner(
                             onContinueClick = onConfirmRecoveryKeyClick,
-                            onDismissClick = { eventSink(RoomListEvents.DismissRecoveryKeyPrompt) }
+                            onDismissClick = { updatedEventSink(RoomListEvents.DismissRecoveryKeyPrompt) }
                         )
                     }
                 }

features/roomlist/impl/src/main/kotlin/io/element/android/features/roomlist/impl/datasource/RoomListDataSource.kt

@@ -20,6 +20,7 @@ import io.element.android.features.roomlist.impl.model.RoomListRoomSummary
 import io.element.android.libraries.androidutils.diff.DiffCacheUpdater
 import io.element.android.libraries.androidutils.diff.MutableListDiffCache
 import io.element.android.libraries.core.coroutine.CoroutineDispatchers
+import io.element.android.libraries.matrix.api.core.RoomId
 import io.element.android.libraries.matrix.api.notificationsettings.NotificationSettingsService
 import io.element.android.libraries.matrix.api.roomlist.RoomListService
 import io.element.android.libraries.matrix.api.roomlist.RoomSummary
@@ -57,6 +58,10 @@ class RoomListDataSource @Inject constructor(
         old?.roomId == new?.roomId
     }
 
+    val allRooms: Flow<ImmutableList<RoomListRoomSummary>> = _allRooms
+
+    val loadingState = roomListService.allRooms.loadingState
+
     fun launchIn(coroutineScope: CoroutineScope) {
         roomListService
             .allRooms
@@ -67,9 +72,9 @@ class RoomListDataSource @Inject constructor(
             .launchIn(coroutineScope)
     }
 
-    val allRooms: Flow<ImmutableList<RoomListRoomSummary>> = _allRooms
-
-    val loadingState = roomListService.allRooms.loadingState
+    suspend fun subscribeToVisibleRooms(roomIds: List<RoomId>) {
+        roomListService.subscribeToVisibleRooms(roomIds)
+    }
 
     @OptIn(FlowPreview::class)
     private fun observeNotificationSettings() {