From 5e6bcbd7ac9c95565ec89f8a78ecd02c29ea7855 Mon Sep 17 00:00:00 2001
From: ganfra <francoisg@matrix.org>
Date: Wed, 17 Jul 2024 15:49:11 +0200
Subject: [PATCH] Performance : do not trigger back pagination when opening
 room.

---
 .../matrix/impl/timeline/RustTimeline.kt      | 31 ++++++++++++++-----
 .../impl/timeline/TimelineItemsSubscriber.kt  |  8 ++---
 2 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/RustTimeline.kt b/libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/RustTimeline.kt
index fb42f27f62..fe2f01925d 100644
--- a/libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/RustTimeline.kt
+++ b/libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/RustTimeline.kt
@@ -81,7 +81,6 @@ import timber.log.Timber
 import uniffi.matrix_sdk_ui.LiveBackPaginationStatus
 import java.io.File
 import java.util.Date
-import java.util.concurrent.atomic.AtomicBoolean
 import org.matrix.rustcomponents.sdk.Timeline as InnerTimeline
 
 private const val PAGINATION_SIZE = 50
@@ -99,7 +98,7 @@ class RustTimeline(
     onNewSyncedEvent: () -> Unit,
 ) : Timeline {
     private val initLatch = CompletableDeferred<Unit>()
-    private val isInit = AtomicBoolean(false)
+    private val isInit = MutableStateFlow(false)
 
     private val _timelineItems: MutableStateFlow<List<MatrixTimelineItem>> =
         MutableStateFlow(emptyList())
@@ -208,7 +207,7 @@ class RustTimeline(
     }
 
     private fun canPaginate(direction: Timeline.PaginationDirection): Boolean {
-        if (!isInit.get()) return false
+        if (!isInit.value) return false
         return when (direction) {
             Timeline.PaginationDirection.BACKWARDS -> backPaginationStatus.value.canPaginate
             Timeline.PaginationDirection.FORWARDS -> forwardPaginationStatus.value.canPaginate
@@ -226,20 +225,25 @@ class RustTimeline(
         _timelineItems,
         backPaginationStatus.map { it.hasMoreToLoad }.distinctUntilChanged(),
         forwardPaginationStatus.map { it.hasMoreToLoad }.distinctUntilChanged(),
-    ) { timelineItems, hasMoreToLoadBackward, hasMoreToLoadForward ->
+        isInit,
+    ) { timelineItems, hasMoreToLoadBackward, hasMoreToLoadForward, isInit ->
         withContext(dispatcher) {
             timelineItems
-                .let { items -> encryptedHistoryPostProcessor.process(items) }
-                .let { items ->
+                .process { items -> encryptedHistoryPostProcessor.process(items) }
+                .process { items ->
                     roomBeginningPostProcessor.process(
                         items = items,
                         isDm = matrixRoom.isDm,
                         hasMoreToLoadBackwards = hasMoreToLoadBackward
                     )
                 }
-                .let { items -> loadingIndicatorsPostProcessor.process(items, hasMoreToLoadBackward, hasMoreToLoadForward) }
+                .process(predicate = isInit) { items ->
+                    loadingIndicatorsPostProcessor.process(items, hasMoreToLoadBackward, hasMoreToLoadForward)
+                }
                 // Keep lastForwardIndicatorsPostProcessor last
-                .let { items -> lastForwardIndicatorsPostProcessor.process(items) }
+                .process(predicate = isInit) { items ->
+                    lastForwardIndicatorsPostProcessor.process(items)
+                }
         }
     }.onStart {
         timelineItemsSubscriber.subscribeIfNeeded()
@@ -545,3 +549,14 @@ class RustTimeline(
         }
     }
 }
+
+private suspend fun List<MatrixTimelineItem>.process(
+    predicate: Boolean = true,
+    processor: suspend (List<MatrixTimelineItem>) -> List<MatrixTimelineItem>
+): List<MatrixTimelineItem> {
+    return if (predicate) {
+        processor(this)
+    } else {
+        this
+    }
+}
diff --git a/libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/TimelineItemsSubscriber.kt b/libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/TimelineItemsSubscriber.kt
index a4086c2810..d5454ff254 100644
--- a/libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/TimelineItemsSubscriber.kt
+++ b/libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/TimelineItemsSubscriber.kt
@@ -23,6 +23,7 @@ import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.cancelChildren
 import kotlinx.coroutines.coroutineScope
 import kotlinx.coroutines.ensureActive
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.launchIn
 import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.sync.Mutex
@@ -32,7 +33,6 @@ import org.matrix.rustcomponents.sdk.TimelineChange
 import org.matrix.rustcomponents.sdk.TimelineDiff
 import org.matrix.rustcomponents.sdk.TimelineItem
 import uniffi.matrix_sdk_ui.EventItemOrigin
-import java.util.concurrent.atomic.AtomicBoolean
 
 private const val INITIAL_MAX_SIZE = 50
 
@@ -47,7 +47,7 @@ internal class TimelineItemsSubscriber(
     private val timeline: Timeline,
     private val timelineDiffProcessor: MatrixTimelineDiffProcessor,
     private val initLatch: CompletableDeferred<Unit>,
-    private val isInit: AtomicBoolean,
+    private val isInit: MutableStateFlow<Boolean>,
     private val onNewSyncedEvent: () -> Unit,
 ) {
     private var subscriptionCount = 0
@@ -94,13 +94,13 @@ internal class TimelineItemsSubscriber(
             ensureActive()
             timelineDiffProcessor.postItems(it)
         }
-        isInit.set(true)
+        isInit.value = true
         initLatch.complete(Unit)
     }
 
     private suspend fun postDiffs(diffs: List<TimelineDiff>) {
         val diffsToProcess = diffs.toMutableList()
-        if (!isInit.get()) {
+        if (!isInit.value) {
             val resetDiff = diffsToProcess.firstOrNull { it.change() == TimelineChange.RESET }
             if (resetDiff != null) {
                 // Keep using the postItems logic so we can post the timelineItems asap.