Timeline: first version of diff/cache

features/messages/build.gradle.kts

@@ -18,6 +18,7 @@ dependencies {
     implementation(libs.timber)
     implementation(libs.datetime)
     implementation(libs.accompanist.flowlayout)
+    implementation(libs.androidx.recyclerview)
     implementation("org.jsoup:jsoup:1.15.3")
     testImplementation("junit:junit:4.13.2")
     androidTestImplementation("androidx.test.ext:junit:1.1.3")

features/messages/src/main/java/io/element/android/x/features/messages/MessageTimelineItemStateFactory.kt

@@ -1,7 +1,10 @@
 package io.element.android.x.features.messages
 
+import androidx.recyclerview.widget.DiffUtil
 import io.element.android.x.designsystem.components.avatar.AvatarData
 import io.element.android.x.designsystem.components.avatar.AvatarSize
+import io.element.android.x.features.messages.diff.CacheInvalidator
+import io.element.android.x.features.messages.diff.MatrixTimelineItemsDiffCallback
 import io.element.android.x.features.messages.model.AggregatedReaction
 import io.element.android.x.features.messages.model.MessagesItemGroupPosition
 import io.element.android.x.features.messages.model.MessagesItemReactionState
@@ -12,44 +15,92 @@ import io.element.android.x.matrix.media.MediaResolver
 import io.element.android.x.matrix.room.MatrixRoom
 import io.element.android.x.matrix.timeline.MatrixTimelineItem
 import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
 import org.jsoup.Jsoup
 import org.jsoup.nodes.Document
 import org.matrix.rustcomponents.sdk.FormattedBody
 import org.matrix.rustcomponents.sdk.MessageFormat
 import org.matrix.rustcomponents.sdk.MessageType
-import org.matrix.rustcomponents.sdk.TimelineKey
+import timber.log.Timber
+import kotlin.system.measureTimeMillis
 
 class MessageTimelineItemStateFactory(
     private val client: MatrixClient,
     private val room: MatrixRoom,
     private val dispatcher: CoroutineDispatcher,
 ) {
+
+    private val timelineItemCaches = arrayListOf<MessagesTimelineItemState?>()
+    private var currentSnapshot: List<MatrixTimelineItem> = emptyList()
+
+    private val lock = Mutex()
+    private val cacheInvalidator = CacheInvalidator(timelineItemCaches)
+
     suspend fun create(
         timelineItems: List<MatrixTimelineItem>,
     ): List<MessagesTimelineItemState> =
         withContext(dispatcher) {
-            val messagesTimelineItemState = ArrayList<MessagesTimelineItemState>()
+            lock.withLock {
-            for (index in timelineItems.indices.reversed()) {
+                calculateAndApplyDiff(timelineItems)
-                val currentTimelineItem = timelineItems[index]
+                getOrCreateFromCache(timelineItems)
-                val timelineItemState = when (currentTimelineItem) {
-                    is MatrixTimelineItem.Event -> {
-                        buildMessageEvent(
-                            currentTimelineItem,
-                            index,
-                            timelineItems,
-                        )
-                    }
-                    is MatrixTimelineItem.Virtual -> MessagesTimelineItemState.Virtual(
-                        "virtual_item_$index"
-                    )
-                    MatrixTimelineItem.Other -> continue
-                }
-                messagesTimelineItemState.add(timelineItemState)
             }
-            messagesTimelineItemState
         }
 
+    private suspend fun getOrCreateFromCache(timelineItems: List<MatrixTimelineItem>): List<MessagesTimelineItemState> {
+        val messagesTimelineItemState = ArrayList<MessagesTimelineItemState>()
+        for (index in timelineItemCaches.indices.reversed()) {
+            val cacheItem = timelineItemCaches[index]
+            if (cacheItem == null) {
+                buildAndCacheItem(timelineItems, index)?.also { timelineItemState ->
+                    messagesTimelineItemState.add(timelineItemState)
+                }
+            } else {
+                messagesTimelineItemState.add(cacheItem)
+            }
+        }
+        return messagesTimelineItemState
+    }
+
+
+    private fun calculateAndApplyDiff(timelineItems: List<MatrixTimelineItem>) {
+        val timeToDiff = measureTimeMillis {
+            val diffCallback =
+                MatrixTimelineItemsDiffCallback(
+                    oldList = currentSnapshot,
+                    newList = timelineItems
+                )
+
+            val diffResult = DiffUtil.calculateDiff(diffCallback, false)
+            currentSnapshot = timelineItems
+            diffResult.dispatchUpdatesTo(cacheInvalidator)
+        }
+        Timber.v("Time to apply diff on new list of ${timelineItems.size} items: $timeToDiff ms")
+    }
+
+    private suspend fun buildAndCacheItem(
+        timelineItems: List<MatrixTimelineItem>,
+        index: Int
+    ): MessagesTimelineItemState? {
+        val timelineItemState =
+            when (val currentTimelineItem = timelineItems[index]) {
+                is MatrixTimelineItem.Event -> {
+                    buildMessageEvent(
+                        currentTimelineItem,
+                        index,
+                        timelineItems,
+                    )
+                }
+                is MatrixTimelineItem.Virtual -> MessagesTimelineItemState.Virtual(
+                    "virtual_item_$index"
+                )
+                MatrixTimelineItem.Other -> null
+            }
+        timelineItemCaches[index] = timelineItemState
+        return timelineItemState
+    }
+
     private suspend fun buildMessageEvent(
         currentTimelineItem: MatrixTimelineItem.Event,
         index: Int,
@@ -62,12 +113,8 @@ class MessageTimelineItemStateFactory(
         val senderAvatarUrl = room.userAvatarUrl(currentSender).getOrNull()
         val senderAvatarData =
             loadAvatarData(senderDisplayName ?: currentSender, senderAvatarUrl)
-        val uniqueId = when (val eventKey = currentTimelineItem.event.key()) {
-            is TimelineKey.TransactionId -> eventKey.txnId
-            is TimelineKey.EventId -> eventKey.eventId
-        }
         return MessagesTimelineItemState.MessageEvent(
-            id = uniqueId,
+            id = currentTimelineItem.uniqueId,
             senderId = currentSender,
             senderDisplayName = senderDisplayName,
             senderAvatar = senderAvatarData,
@@ -166,6 +213,4 @@ class MessageTimelineItemStateFactory(
             .resolve(url, kind = MediaResolver.Kind.Thumbnail(size.value))
         return AvatarData(name, model, size)
     }
-
+}
-
-}

features/messages/src/main/java/io/element/android/x/features/messages/diff/CacheInvalidator.kt

@@ -0,0 +1,38 @@
+package io.element.android.x.features.messages.diff
+
+import androidx.recyclerview.widget.ListUpdateCallback
+import io.element.android.x.features.messages.model.MessagesTimelineItemState
+import timber.log.Timber
+
+internal class CacheInvalidator(private val timelineItemCache: MutableList<MessagesTimelineItemState?>) :
+    ListUpdateCallback {
+
+    override fun onChanged(position: Int, count: Int, payload: Any?) {
+        Timber.v("onChanged(position= $position, count= $count")
+        (position until position + count).forEach {
+            // Invalidate cache
+            timelineItemCache[it] = null
+        }
+    }
+
+    override fun onMoved(fromPosition: Int, toPosition: Int) {
+        Timber.v("onMoved(fromPosition= $fromPosition, toPosition= $toPosition")
+        val model = timelineItemCache.removeAt(fromPosition)
+        timelineItemCache.add(toPosition, model)
+    }
+
+    override fun onInserted(position: Int, count: Int) {
+        Timber.v("onInserted(position= $position, count= $count")
+        repeat(count) {
+            timelineItemCache.add(position, null)
+        }
+    }
+
+    override fun onRemoved(position: Int, count: Int) {
+        Timber.v("onRemoved(position= $position, count= $count")
+        repeat(count) {
+            timelineItemCache.removeAt(position)
+        }
+    }
+
+}

features/messages/src/main/java/io/element/android/x/features/messages/diff/MatrixTimelineItemsDiffCallback.kt

@@ -0,0 +1,35 @@
+package io.element.android.x.features.messages.diff
+
+import androidx.recyclerview.widget.DiffUtil
+import io.element.android.x.matrix.timeline.MatrixTimelineItem
+
+internal class MatrixTimelineItemsDiffCallback(
+    private val oldList: List<MatrixTimelineItem>,
+    private val newList: List<MatrixTimelineItem>
+) : DiffUtil.Callback() {
+
+    override fun getOldListSize(): Int {
+        return oldList.size
+    }
+
+    override fun getNewListSize(): Int {
+        return newList.size
+    }
+
+    override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
+        val oldItem = oldList.getOrNull(oldItemPosition)
+        val newItem = newList.getOrNull(newItemPosition)
+        return if (oldItem is MatrixTimelineItem.Event && newItem is MatrixTimelineItem.Event) {
+            oldItem.uniqueId == newItem.uniqueId
+        } else {
+            false
+        }
+    }
+
+    override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
+        val oldItem = oldList.getOrNull(oldItemPosition)
+        val newItem = newList.getOrNull(newItemPosition)
+        return oldItem == newItem
+    }
+
+}

gradle/libs.versions.toml

@@ -10,6 +10,7 @@ material = "1.6.1"
 corektx = "1.9.0"
 datastore = "1.0.0"
 constraintlayout = "2.1.4"
+recyclerview = "1.2.1"
 
 # Compose
 compose_compiler = "1.3.2"
@@ -52,6 +53,7 @@ androidx_corektx = { module = "androidx.core:core-ktx", version.ref = "corektx"
 androidx_datastore_preferences = { module = "androidx.datastore:datastore-preferences", version.ref = "datastore" }
 androidx_datastore_datastore = { module = "androidx.datastore:datastore", version.ref = "datastore" }
 androidx_constraintlayout = { module = "androidx.constraintlayout:constraintlayout", version.ref = "constraintlayout" }
+androidx_recyclerview = { module = "androidx.recyclerview:recyclerview", version.ref = "recyclerview" }
 
 androidx_compose_bom = { group = "androidx.compose", name = "compose-bom", version.ref = "compose_bom" }
 androidx_compose_foundation = { group = "androidx.compose.foundation", name = "foundation" }

libraries/matrix/src/main/java/io/element/android/x/matrix/timeline/MatrixTimelineItem.kt

@@ -2,9 +2,17 @@ package io.element.android.x.matrix.timeline
 
 import org.matrix.rustcomponents.sdk.EventTimelineItem
 import org.matrix.rustcomponents.sdk.TimelineItem
+import org.matrix.rustcomponents.sdk.TimelineKey
 
 sealed interface MatrixTimelineItem {
-    data class Event(val event: EventTimelineItem) : MatrixTimelineItem
+    data class Event(val event: EventTimelineItem) : MatrixTimelineItem {
+        val uniqueId: String
+            get() = when (val eventKey = event.key()) {
+                is TimelineKey.TransactionId -> eventKey.txnId
+                is TimelineKey.EventId -> eventKey.eventId
+            }
+    }
+
     object Virtual : MatrixTimelineItem
     object Other : MatrixTimelineItem
 }