Merge pull request #2830 from vector-im/feature/fga/fix_some_voip_issues

Feature/fga/fix some voip issues

.idea/dictionaries/bmarty.xml

@@ -26,6 +26,7 @@
       <w>pkcs</w>
       <w>previewable</w>
       <w>previewables</w>
+      <w>pstn</w>
       <w>riotx</w>
       <w>signin</w>
       <w>signout</w>

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/call/CallSignalingService.kt

@@ -16,12 +16,11 @@
 
 package org.matrix.android.sdk.api.session.call
 
-import org.matrix.android.sdk.api.MatrixCallback
-import org.matrix.android.sdk.api.util.Cancelable
-
 interface CallSignalingService {
 
-    fun getTurnServer(callback: MatrixCallback<TurnServerResponse>): Cancelable
+    suspend fun getTurnServer(): TurnServerResponse
+
+    fun getPSTNProtocolChecker(): PSTNProtocolChecker
 
     /**
      * Create an outgoing call

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/call/PSTNProtocolChecker.kt

@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2021 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.matrix.android.sdk.api.session.call
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
+import org.matrix.android.sdk.api.extensions.tryOrNull
+import org.matrix.android.sdk.api.session.room.model.thirdparty.ThirdPartyProtocol
+import org.matrix.android.sdk.internal.session.SessionScope
+import org.matrix.android.sdk.internal.session.thirdparty.GetThirdPartyProtocolsTask
+import org.matrix.android.sdk.internal.task.TaskExecutor
+import timber.log.Timber
+import java.util.concurrent.atomic.AtomicBoolean
+import javax.inject.Inject
+
+private const val PSTN_VECTOR_KEY = "im.vector.protocol.pstn"
+private const val PSTN_MATRIX_KEY = "m.protocol.pstn"
+
+/**
+ * This class is responsible for checking if the HS support the PSTN protocol.
+ * As long as the request succeed, it'll check only once by session.
+ */
+@SessionScope
+class PSTNProtocolChecker @Inject internal constructor(private val taskExecutor: TaskExecutor,
+                                                       private val getThirdPartyProtocolsTask: GetThirdPartyProtocolsTask) {
+
+    interface Listener {
+        fun onPSTNSupportUpdated()
+    }
+
+    private var alreadyChecked = AtomicBoolean(false)
+
+    private val pstnSupportListeners = mutableListOf<Listener>()
+
+    fun addListener(listener: Listener) {
+        pstnSupportListeners.add(listener)
+    }
+
+    fun removeListener(listener: Listener) {
+        pstnSupportListeners.remove(listener)
+    }
+
+    var supportedPSTNProtocol: String? = null
+        private set
+
+    fun checkForPSTNSupportIfNeeded() {
+        if (alreadyChecked.get()) return
+        taskExecutor.executorScope.checkForPSTNSupport()
+    }
+
+    private fun CoroutineScope.checkForPSTNSupport() = launch {
+        try {
+            supportedPSTNProtocol = getSupportedPSTN(3)
+            alreadyChecked.set(true)
+            if (supportedPSTNProtocol != null) {
+                pstnSupportListeners.forEach {
+                    tryOrNull { it.onPSTNSupportUpdated() }
+                }
+            }
+        } catch (failure: Throwable) {
+            Timber.v("Fail to get supported PSTN, will check again next time.")
+        }
+    }
+
+    private suspend fun getSupportedPSTN(maxTries: Int): String? {
+        val thirdPartyProtocols: Map<String, ThirdPartyProtocol> = try {
+            getThirdPartyProtocolsTask.execute(Unit)
+        } catch (failure: Throwable) {
+            if (maxTries == 1) {
+                throw failure
+            } else {
+                // Wait for 10s before trying again
+                delay(10_000L)
+                return getSupportedPSTN(maxTries - 1)
+            }
+        }
+        return when {
+            thirdPartyProtocols.containsKey(PSTN_VECTOR_KEY) -> PSTN_VECTOR_KEY
+            thirdPartyProtocols.containsKey(PSTN_MATRIX_KEY) -> PSTN_MATRIX_KEY
+            else                                             -> null
+        }
+    }
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/call/DefaultCallSignalingService.kt

@@ -16,16 +16,12 @@
 
 package org.matrix.android.sdk.internal.session.call
 
-import kotlinx.coroutines.Dispatchers
-import org.matrix.android.sdk.api.MatrixCallback
 import org.matrix.android.sdk.api.session.call.CallListener
 import org.matrix.android.sdk.api.session.call.CallSignalingService
 import org.matrix.android.sdk.api.session.call.MxCall
+import org.matrix.android.sdk.api.session.call.PSTNProtocolChecker
 import org.matrix.android.sdk.api.session.call.TurnServerResponse
-import org.matrix.android.sdk.api.util.Cancelable
 import org.matrix.android.sdk.internal.session.SessionScope
-import org.matrix.android.sdk.internal.task.TaskExecutor
-import org.matrix.android.sdk.internal.task.launchToCallback
 import timber.log.Timber
 import javax.inject.Inject
 
@@ -34,14 +30,16 @@ internal class DefaultCallSignalingService @Inject constructor(
         private val callSignalingHandler: CallSignalingHandler,
         private val mxCallFactory: MxCallFactory,
         private val activeCallHandler: ActiveCallHandler,
-        private val taskExecutor: TaskExecutor,
+        private val turnServerDataSource: TurnServerDataSource,
-        private val turnServerDataSource: TurnServerDataSource
+        private val pstnProtocolChecker: PSTNProtocolChecker
 ) : CallSignalingService {
 
-    override fun getTurnServer(callback: MatrixCallback<TurnServerResponse>): Cancelable {
+    override suspend fun getTurnServer(): TurnServerResponse {
-        return taskExecutor.executorScope.launchToCallback(Dispatchers.Default, callback) {
+        return turnServerDataSource.getTurnServer()
-            turnServerDataSource.getTurnServer()
+    }
-        }
+
+    override fun getPSTNProtocolChecker(): PSTNProtocolChecker {
+        return pstnProtocolChecker
     }
 
     override fun createOutgoingCall(roomId: String, otherUserId: String, isVideoCall: Boolean): MxCall {

vector/src/main/java/im/vector/app/core/epoxy/TimelineEmptyItem.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2019 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package im.vector.app.core.epoxy
+
+import com.airbnb.epoxy.EpoxyAttribute
+import com.airbnb.epoxy.EpoxyModelClass
+import im.vector.app.R
+import im.vector.app.features.home.room.detail.timeline.item.ItemWithEvents
+
+@EpoxyModelClass(layout = R.layout.item_timeline_empty)
+abstract class TimelineEmptyItem : VectorEpoxyModel<TimelineEmptyItem.Holder>(), ItemWithEvents {
+
+    @EpoxyAttribute lateinit var eventId: String
+
+    override fun getEventIds(): List<String> {
+        return listOf(eventId)
+    }
+
+    class Holder : VectorEpoxyHolder()
+}

vector/src/main/java/im/vector/app/features/call/VectorCallViewModel.kt

@@ -16,6 +16,7 @@
 
 package im.vector.app.features.call
 
+import androidx.lifecycle.viewModelScope
 import com.airbnb.mvrx.Fail
 import com.airbnb.mvrx.Loading
 import com.airbnb.mvrx.MvRxViewModelFactory
@@ -29,17 +30,16 @@ import im.vector.app.core.platform.VectorViewModel
 import im.vector.app.features.call.audio.CallAudioManager
 import im.vector.app.features.call.webrtc.WebRtcCall
 import im.vector.app.features.call.webrtc.WebRtcCallManager
-import org.matrix.android.sdk.api.MatrixCallback
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
 import org.matrix.android.sdk.api.session.Session
 import org.matrix.android.sdk.api.session.call.CallState
 import org.matrix.android.sdk.api.session.call.MxCall
 import org.matrix.android.sdk.api.session.call.MxPeerConnectionState
-import org.matrix.android.sdk.api.session.call.TurnServerResponse
 import org.matrix.android.sdk.api.session.room.model.call.supportCallTransfer
 import org.matrix.android.sdk.api.util.MatrixItem
 import org.matrix.android.sdk.api.util.toMatrixItem
-import java.util.Timer
-import java.util.TimerTask
 
 class VectorCallViewModel @AssistedInject constructor(
         @Assisted initialState: VectorCallViewState,
@@ -50,7 +50,7 @@ class VectorCallViewModel @AssistedInject constructor(
 
     private var call: WebRtcCall? = null
 
-    private var connectionTimeoutTimer: Timer? = null
+    private var connectionTimeoutJob: Job? = null
     private var hasBeenConnectedOnce = false
 
     private val callListener = object : WebRtcCall.Listener {
@@ -92,26 +92,20 @@ class VectorCallViewModel @AssistedInject constructor(
             val callState = call.state
             if (callState is CallState.Connected && callState.iceConnectionState == MxPeerConnectionState.CONNECTED) {
                 hasBeenConnectedOnce = true
-                connectionTimeoutTimer?.cancel()
+                connectionTimeoutJob?.cancel()
-                connectionTimeoutTimer = null
+                connectionTimeoutJob = null
             } else {
                 // do we reset as long as it's moving?
-                connectionTimeoutTimer?.cancel()
+                connectionTimeoutJob?.cancel()
                 if (hasBeenConnectedOnce) {
-                    connectionTimeoutTimer = Timer().apply {
+                    connectionTimeoutJob = viewModelScope.launch {
-                        schedule(object : TimerTask() {
+                        delay(30_000)
-                            override fun run() {
+                        try {
-                                session.callSignalingService().getTurnServer(object : MatrixCallback<TurnServerResponse> {
+                            val turn = session.callSignalingService().getTurnServer()
-                                    override fun onFailure(failure: Throwable) {
+                            _viewEvents.post(VectorCallViewEvents.ConnectionTimeout(turn))
-                                        _viewEvents.post(VectorCallViewEvents.ConnectionTimeout(null))
+                        } catch (failure: Throwable) {
-                                    }
+                            _viewEvents.post(VectorCallViewEvents.ConnectionTimeout(null))
-
+                        }
-                                    override fun onSuccess(data: TurnServerResponse) {
-                                        _viewEvents.post(VectorCallViewEvents.ConnectionTimeout(data))
-                                    }
-                                })
-                            }
-                        }, 30_000)
                     }
                 }
             }

vector/src/main/java/im/vector/app/features/call/dialpad/DialPadLookup.kt

@@ -22,20 +22,22 @@ import org.matrix.android.sdk.api.extensions.tryOrNull
 import org.matrix.android.sdk.api.session.Session
 import javax.inject.Inject
 
-class DialPadLookup @Inject constructor(val session: Session,
+class DialPadLookup @Inject constructor(
-                                        val directRoomHelper: DirectRoomHelper,
+        private val session: Session,
-                                        val callManager: WebRtcCallManager
+        private val directRoomHelper: DirectRoomHelper,
+        private val callManager: WebRtcCallManager
 ) {
-
     class Failure : Throwable()
+
     data class Result(val userId: String, val roomId: String)
 
     suspend fun lookupPhoneNumber(phoneNumber: String): Result {
         val supportedProtocolKey = callManager.supportedPSTNProtocol ?: throw Failure()
         val thirdPartyUser = tryOrNull {
-            session.thirdPartyService().getThirdPartyUser(supportedProtocolKey, fields = mapOf(
+            session.thirdPartyService().getThirdPartyUser(
-                    "m.id.phone" to phoneNumber
+                    protocol = supportedProtocolKey,
-            )).firstOrNull()
+                    fields = mapOf("m.id.phone" to phoneNumber)
+            ).firstOrNull()
         } ?: throw Failure()
 
         val roomId = directRoomHelper.ensureDMExists(thirdPartyUser.userId)

vector/src/main/java/im/vector/app/features/call/webrtc/PSTNProtocol.kt

@@ -1,43 +0,0 @@
-/*
- * Copyright (c) 2021 New Vector Ltd
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package im.vector.app.features.call.webrtc
-
-import kotlinx.coroutines.delay
-import org.matrix.android.sdk.api.session.Session
-import org.matrix.android.sdk.api.session.room.model.thirdparty.ThirdPartyProtocol
-
-private const val PSTN_VECTOR_KEY = "im.vector.protocol.pstn"
-private const val PSTN_MATRIX_KEY = "m.protocol.pstn"
-
-suspend fun Session.getSupportedPSTN(maxTries: Int): String? {
-    val thirdPartyProtocols: Map<String, ThirdPartyProtocol> = try {
-        thirdPartyService().getThirdPartyProtocols()
-    } catch (failure: Throwable) {
-        if (maxTries == 1) {
-            return null
-        } else {
-            // Wait for 10s before trying again
-            delay(10_000L)
-            return getSupportedPSTN(maxTries - 1)
-        }
-    }
-    return when {
-        thirdPartyProtocols.containsKey(PSTN_VECTOR_KEY) -> PSTN_VECTOR_KEY
-        thirdPartyProtocols.containsKey(PSTN_MATRIX_KEY) -> PSTN_MATRIX_KEY
-        else                                             -> null
-    }
-}

vector/src/main/java/im/vector/app/features/call/webrtc/WebRtcCall.kt

@@ -53,7 +53,6 @@ import org.matrix.android.sdk.api.session.room.model.call.CallHangupContent
 import org.matrix.android.sdk.api.session.room.model.call.CallInviteContent
 import org.matrix.android.sdk.api.session.room.model.call.CallNegotiateContent
 import org.matrix.android.sdk.api.session.room.model.call.SdpType
-import org.matrix.android.sdk.internal.util.awaitCallback
 import org.threeten.bp.Duration
 import org.webrtc.AudioSource
 import org.webrtc.AudioTrack
@@ -420,9 +419,7 @@ class WebRtcCall(val mxCall: MxCall,
 
     private suspend fun getTurnServer(): TurnServerResponse? {
         return tryOrNull {
-            awaitCallback {
+            sessionProvider.get()?.callSignalingService()?.getTurnServer()
-                sessionProvider.get()?.callSignalingService()?.getTurnServer(it)
-            }
         }
     }
 

vector/src/main/java/im/vector/app/features/call/webrtc/WebRtcCallManager.kt

@@ -26,14 +26,13 @@ import im.vector.app.features.call.VectorCallActivity
 import im.vector.app.features.call.audio.CallAudioManager
 import im.vector.app.features.call.utils.EglUtils
 import im.vector.app.push.fcm.FcmHelper
-import kotlinx.coroutines.GlobalScope
 import kotlinx.coroutines.asCoroutineDispatcher
-import kotlinx.coroutines.launch
 import org.matrix.android.sdk.api.extensions.tryOrNull
 import org.matrix.android.sdk.api.session.Session
 import org.matrix.android.sdk.api.session.call.CallListener
 import org.matrix.android.sdk.api.session.call.CallState
 import org.matrix.android.sdk.api.session.call.MxCall
+import org.matrix.android.sdk.api.session.call.PSTNProtocolChecker
 import org.matrix.android.sdk.api.session.room.model.call.CallAnswerContent
 import org.matrix.android.sdk.api.session.room.model.call.CallCandidatesContent
 import org.matrix.android.sdk.api.session.room.model.call.CallHangupContent
@@ -65,22 +64,26 @@ class WebRtcCallManager @Inject constructor(
     private val currentSession: Session?
         get() = activeSessionDataSource.currentValue?.orNull()
 
+    private val pstnProtocolChecker: PSTNProtocolChecker?
+        get() = currentSession?.callSignalingService()?.getPSTNProtocolChecker()
+
     interface CurrentCallListener {
         fun onCurrentCallChange(call: WebRtcCall?) {}
         fun onAudioDevicesChange() {}
     }
 
-    interface PSTNSupportListener {
+    val supportedPSTNProtocol: String?
-        fun onPSTNSupportUpdated()
+        get() = pstnProtocolChecker?.supportedPSTNProtocol
+
+    val supportsPSTNProtocol: Boolean
+        get() = supportedPSTNProtocol != null
+
+    fun addPstnSupportListener(listener: PSTNProtocolChecker.Listener) {
+        pstnProtocolChecker?.addListener(listener)
     }
 
-    private val pstnSupportListeners = emptyList<PSTNSupportListener>().toMutableList()
+    fun removePstnSupportListener(listener: PSTNProtocolChecker.Listener) {
-    fun addPstnSupportListener(listener: PSTNSupportListener) {
+        pstnProtocolChecker?.removeListener(listener)
-        pstnSupportListeners.add(listener)
-    }
-
-    fun removePstnSupportListener(listener: PSTNSupportListener) {
-        pstnSupportListeners.remove(listener)
     }
 
     private val currentCallsListeners = CopyOnWriteArrayList<CurrentCallListener>()
@@ -104,27 +107,11 @@ class WebRtcCallManager @Inject constructor(
     private var peerConnectionFactory: PeerConnectionFactory? = null
     private val executor = Executors.newSingleThreadExecutor()
     private val dispatcher = executor.asCoroutineDispatcher()
-    var supportedPSTNProtocol: String? = null
-        private set
-
-    val supportsPSTNProtocol: Boolean
-        get() = supportedPSTNProtocol != null
 
     private val rootEglBase by lazy { EglUtils.rootEglBase }
 
     private var isInBackground: Boolean = true
 
-    init {
-        GlobalScope.launch {
-            supportedPSTNProtocol = currentSession?.getSupportedPSTN(3)
-            if (supportedPSTNProtocol != null) {
-                pstnSupportListeners.forEach {
-                    tryOrNull { it.onPSTNSupportUpdated() }
-                }
-            }
-        }
-    }
-
     @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
     fun entersForeground() {
         isInBackground = false
@@ -167,6 +154,10 @@ class WebRtcCallManager @Inject constructor(
         return callsByCallId.values.toList()
     }
 
+    fun checkForPSTNSupportIfNeeded() {
+        pstnProtocolChecker?.checkForPSTNSupportIfNeeded()
+    }
+
     /**
      * @return a set of all advertised call during the lifetime of the app.
      */
@@ -176,7 +167,6 @@ class WebRtcCallManager @Inject constructor(
         Timber.v("## VOIP headSetButtonTapped")
         val call = getCurrentCall() ?: return
         if (call.mxCall.state is CallState.LocalRinging) {
-            // accept call
             call.acceptIncomingCall()
         }
         if (call.mxCall.state is CallState.Connected) {

vector/src/main/java/im/vector/app/features/home/room/detail/RoomDetailViewModel.kt

@@ -26,8 +26,8 @@ import com.airbnb.mvrx.ViewModelContext
 import com.jakewharton.rxrelay2.BehaviorRelay
 import com.jakewharton.rxrelay2.PublishRelay
 import dagger.assisted.Assisted
-import dagger.assisted.AssistedInject
 import dagger.assisted.AssistedFactory
+import dagger.assisted.AssistedInject
 import im.vector.app.R
 import im.vector.app.core.extensions.exhaustive
 import im.vector.app.core.platform.VectorViewModel
@@ -64,6 +64,7 @@ import org.matrix.android.sdk.api.extensions.tryOrNull
 import org.matrix.android.sdk.api.query.QueryStringValue
 import org.matrix.android.sdk.api.raw.RawService
 import org.matrix.android.sdk.api.session.Session
+import org.matrix.android.sdk.api.session.call.PSTNProtocolChecker
 import org.matrix.android.sdk.api.session.crypto.MXCryptoError
 import org.matrix.android.sdk.api.session.events.model.EventType
 import org.matrix.android.sdk.api.session.events.model.LocalEcho
@@ -120,7 +121,7 @@ class RoomDetailViewModel @AssistedInject constructor(
         private val directRoomHelper: DirectRoomHelper,
         timelineSettingsFactory: TimelineSettingsFactory
 ) : VectorViewModel<RoomDetailViewState, RoomDetailAction, RoomDetailViewEvents>(initialState),
-        Timeline.Listener, ChatEffectManager.Delegate, WebRtcCallManager.PSTNSupportListener {
+        Timeline.Listener, ChatEffectManager.Delegate, PSTNProtocolChecker.Listener {
 
     private val room = session.getRoom(initialState.roomId)!!
     private val eventId = initialState.eventId
@@ -176,6 +177,7 @@ class RoomDetailViewModel @AssistedInject constructor(
         // Inform the SDK that the room is displayed
         session.onRoomDisplayed(initialState.roomId)
         callManager.addPstnSupportListener(this)
+        callManager.checkForPSTNSupportIfNeeded()
         chatEffectManager.delegate = this
     }
 
@@ -231,65 +233,65 @@ class RoomDetailViewModel @AssistedInject constructor(
 
     override fun handle(action: RoomDetailAction) {
         when (action) {
-            is RoomDetailAction.UserIsTyping                     -> handleUserIsTyping(action)
+            is RoomDetailAction.UserIsTyping -> handleUserIsTyping(action)
-            is RoomDetailAction.SaveDraft                        -> handleSaveDraft(action)
+            is RoomDetailAction.SaveDraft -> handleSaveDraft(action)
-            is RoomDetailAction.SendMessage                      -> handleSendMessage(action)
+            is RoomDetailAction.SendMessage -> handleSendMessage(action)
-            is RoomDetailAction.SendMedia                        -> handleSendMedia(action)
+            is RoomDetailAction.SendMedia -> handleSendMedia(action)
-            is RoomDetailAction.SendSticker                      -> handleSendSticker(action)
+            is RoomDetailAction.SendSticker -> handleSendSticker(action)
-            is RoomDetailAction.TimelineEventTurnsVisible        -> handleEventVisible(action)
+            is RoomDetailAction.TimelineEventTurnsVisible -> handleEventVisible(action)
-            is RoomDetailAction.TimelineEventTurnsInvisible      -> handleEventInvisible(action)
+            is RoomDetailAction.TimelineEventTurnsInvisible -> handleEventInvisible(action)
-            is RoomDetailAction.LoadMoreTimelineEvents           -> handleLoadMore(action)
+            is RoomDetailAction.LoadMoreTimelineEvents -> handleLoadMore(action)
-            is RoomDetailAction.SendReaction                     -> handleSendReaction(action)
+            is RoomDetailAction.SendReaction -> handleSendReaction(action)
-            is RoomDetailAction.AcceptInvite                     -> handleAcceptInvite()
+            is RoomDetailAction.AcceptInvite -> handleAcceptInvite()
-            is RoomDetailAction.RejectInvite                     -> handleRejectInvite()
+            is RoomDetailAction.RejectInvite -> handleRejectInvite()
-            is RoomDetailAction.RedactAction                     -> handleRedactEvent(action)
+            is RoomDetailAction.RedactAction -> handleRedactEvent(action)
-            is RoomDetailAction.UndoReaction                     -> handleUndoReact(action)
+            is RoomDetailAction.UndoReaction -> handleUndoReact(action)
-            is RoomDetailAction.UpdateQuickReactAction           -> handleUpdateQuickReaction(action)
+            is RoomDetailAction.UpdateQuickReactAction -> handleUpdateQuickReaction(action)
-            is RoomDetailAction.EnterRegularMode                 -> handleEnterRegularMode(action)
+            is RoomDetailAction.EnterRegularMode -> handleEnterRegularMode(action)
-            is RoomDetailAction.EnterEditMode                    -> handleEditAction(action)
+            is RoomDetailAction.EnterEditMode -> handleEditAction(action)
-            is RoomDetailAction.EnterQuoteMode                   -> handleQuoteAction(action)
+            is RoomDetailAction.EnterQuoteMode -> handleQuoteAction(action)
-            is RoomDetailAction.EnterReplyMode                   -> handleReplyAction(action)
+            is RoomDetailAction.EnterReplyMode -> handleReplyAction(action)
-            is RoomDetailAction.DownloadOrOpen                   -> handleOpenOrDownloadFile(action)
+            is RoomDetailAction.DownloadOrOpen -> handleOpenOrDownloadFile(action)
-            is RoomDetailAction.NavigateToEvent                  -> handleNavigateToEvent(action)
+            is RoomDetailAction.NavigateToEvent -> handleNavigateToEvent(action)
-            is RoomDetailAction.HandleTombstoneEvent             -> handleTombstoneEvent(action)
+            is RoomDetailAction.HandleTombstoneEvent -> handleTombstoneEvent(action)
-            is RoomDetailAction.ResendMessage                    -> handleResendEvent(action)
+            is RoomDetailAction.ResendMessage -> handleResendEvent(action)
-            is RoomDetailAction.RemoveFailedEcho                 -> handleRemove(action)
+            is RoomDetailAction.RemoveFailedEcho -> handleRemove(action)
-            is RoomDetailAction.ResendAll                        -> handleResendAll()
+            is RoomDetailAction.ResendAll -> handleResendAll()
-            is RoomDetailAction.MarkAllAsRead                    -> handleMarkAllAsRead()
+            is RoomDetailAction.MarkAllAsRead -> handleMarkAllAsRead()
-            is RoomDetailAction.ReportContent                    -> handleReportContent(action)
+            is RoomDetailAction.ReportContent -> handleReportContent(action)
-            is RoomDetailAction.IgnoreUser                       -> handleIgnoreUser(action)
+            is RoomDetailAction.IgnoreUser -> handleIgnoreUser(action)
             is RoomDetailAction.EnterTrackingUnreadMessagesState -> startTrackingUnreadMessages()
-            is RoomDetailAction.ExitTrackingUnreadMessagesState  -> stopTrackingUnreadMessages()
+            is RoomDetailAction.ExitTrackingUnreadMessagesState -> stopTrackingUnreadMessages()
-            is RoomDetailAction.ReplyToOptions                   -> handleReplyToOptions(action)
+            is RoomDetailAction.ReplyToOptions -> handleReplyToOptions(action)
-            is RoomDetailAction.AcceptVerificationRequest        -> handleAcceptVerification(action)
+            is RoomDetailAction.AcceptVerificationRequest -> handleAcceptVerification(action)
-            is RoomDetailAction.DeclineVerificationRequest       -> handleDeclineVerification(action)
+            is RoomDetailAction.DeclineVerificationRequest -> handleDeclineVerification(action)
-            is RoomDetailAction.RequestVerification              -> handleRequestVerification(action)
+            is RoomDetailAction.RequestVerification -> handleRequestVerification(action)
-            is RoomDetailAction.ResumeVerification               -> handleResumeRequestVerification(action)
+            is RoomDetailAction.ResumeVerification -> handleResumeRequestVerification(action)
-            is RoomDetailAction.ReRequestKeys                    -> handleReRequestKeys(action)
+            is RoomDetailAction.ReRequestKeys -> handleReRequestKeys(action)
-            is RoomDetailAction.TapOnFailedToDecrypt             -> handleTapOnFailedToDecrypt(action)
+            is RoomDetailAction.TapOnFailedToDecrypt -> handleTapOnFailedToDecrypt(action)
-            is RoomDetailAction.SelectStickerAttachment          -> handleSelectStickerAttachment()
+            is RoomDetailAction.SelectStickerAttachment -> handleSelectStickerAttachment()
-            is RoomDetailAction.OpenIntegrationManager           -> handleOpenIntegrationManager()
+            is RoomDetailAction.OpenIntegrationManager -> handleOpenIntegrationManager()
-            is RoomDetailAction.StartCallWithPhoneNumber         -> handleStartCallWithPhoneNumber(action)
+            is RoomDetailAction.StartCallWithPhoneNumber -> handleStartCallWithPhoneNumber(action)
-            is RoomDetailAction.StartCall                        -> handleStartCall(action)
+            is RoomDetailAction.StartCall -> handleStartCall(action)
-            is RoomDetailAction.AcceptCall                       -> handleAcceptCall(action)
+            is RoomDetailAction.AcceptCall -> handleAcceptCall(action)
-            is RoomDetailAction.EndCall                          -> handleEndCall()
+            is RoomDetailAction.EndCall -> handleEndCall()
-            is RoomDetailAction.ManageIntegrations               -> handleManageIntegrations()
+            is RoomDetailAction.ManageIntegrations -> handleManageIntegrations()
-            is RoomDetailAction.AddJitsiWidget                   -> handleAddJitsiConference(action)
+            is RoomDetailAction.AddJitsiWidget -> handleAddJitsiConference(action)
-            is RoomDetailAction.RemoveWidget                     -> handleDeleteWidget(action.widgetId)
+            is RoomDetailAction.RemoveWidget -> handleDeleteWidget(action.widgetId)
-            is RoomDetailAction.EnsureNativeWidgetAllowed        -> handleCheckWidgetAllowed(action)
+            is RoomDetailAction.EnsureNativeWidgetAllowed -> handleCheckWidgetAllowed(action)
-            is RoomDetailAction.CancelSend                       -> handleCancel(action)
+            is RoomDetailAction.CancelSend -> handleCancel(action)
-            is RoomDetailAction.OpenOrCreateDm                   -> handleOpenOrCreateDm(action)
+            is RoomDetailAction.OpenOrCreateDm -> handleOpenOrCreateDm(action)
-            is RoomDetailAction.JumpToReadReceipt                -> handleJumpToReadReceipt(action)
+            is RoomDetailAction.JumpToReadReceipt -> handleJumpToReadReceipt(action)
-            RoomDetailAction.QuickActionInvitePeople             -> handleInvitePeople()
+            RoomDetailAction.QuickActionInvitePeople -> handleInvitePeople()
-            RoomDetailAction.QuickActionSetAvatar                -> handleQuickSetAvatar()
+            RoomDetailAction.QuickActionSetAvatar -> handleQuickSetAvatar()
-            is RoomDetailAction.SetAvatarAction                  -> handleSetNewAvatar(action)
+            is RoomDetailAction.SetAvatarAction -> handleSetNewAvatar(action)
-            RoomDetailAction.QuickActionSetTopic                 -> _viewEvents.post(RoomDetailViewEvents.OpenRoomSettings)
+            RoomDetailAction.QuickActionSetTopic -> _viewEvents.post(RoomDetailViewEvents.OpenRoomSettings)
-            is RoomDetailAction.ShowRoomAvatarFullScreen         -> {
+            is RoomDetailAction.ShowRoomAvatarFullScreen -> {
                 _viewEvents.post(
                         RoomDetailViewEvents.ShowRoomAvatarFullScreen(action.matrixItem, action.transitionView)
                 )
             }
-            is RoomDetailAction.DoNotShowPreviewUrlFor           -> handleDoNotShowPreviewUrlFor(action)
+            is RoomDetailAction.DoNotShowPreviewUrlFor -> handleDoNotShowPreviewUrlFor(action)
         }.exhaustive
     }
 
@@ -618,10 +620,10 @@ class RoomDetailViewModel @AssistedInject constructor(
             return@withState false
         }
         when (itemId) {
-            R.id.resend_all       -> state.asyncRoomSummary()?.hasFailedSending == true
+            R.id.resend_all -> state.asyncRoomSummary()?.hasFailedSending == true
             R.id.timeline_setting -> true
-            R.id.invite           -> state.canInvite
+            R.id.invite -> state.canInvite
-            R.id.clear_all        -> state.asyncRoomSummary()?.hasFailedSending == true
+            R.id.clear_all -> state.asyncRoomSummary()?.hasFailedSending == true
             R.id.open_matrix_apps -> true
             R.id.voice_call,
             R.id.video_call       -> callManager.getCallsByRoomId(state.roomId).isEmpty()
@@ -741,7 +743,7 @@ class RoomDetailViewModel @AssistedInject constructor(
                             _viewEvents.post(RoomDetailViewEvents.SlashCommandHandled())
                             popDraft()
                         }
-                        is ParsedCommand.SendChatEffect            -> {
+                        is ParsedCommand.SendChatEffect           -> {
                             sendChatEffect(slashCommandResult)
                             _viewEvents.post(RoomDetailViewEvents.SlashCommandHandled())
                             popDraft()
@@ -774,7 +776,7 @@ class RoomDetailViewModel @AssistedInject constructor(
                         }
                     }.exhaustive
                 }
-                is SendMode.EDIT    -> {
+                is SendMode.EDIT -> {
                     // is original event a reply?
                     val inReplyTo = state.sendMode.timelineEvent.getRelationContent()?.inReplyTo?.eventId
                     if (inReplyTo != null) {
@@ -799,7 +801,7 @@ class RoomDetailViewModel @AssistedInject constructor(
                     _viewEvents.post(RoomDetailViewEvents.MessageSent)
                     popDraft()
                 }
-                is SendMode.QUOTE   -> {
+                is SendMode.QUOTE -> {
                     val messageContent: MessageContent? =
                             state.sendMode.timelineEvent.annotations?.editSummary?.aggregatedContent.toModel()
                                     ?: state.sendMode.timelineEvent.root.getClearContent().toModel()
@@ -822,7 +824,7 @@ class RoomDetailViewModel @AssistedInject constructor(
                     _viewEvents.post(RoomDetailViewEvents.MessageSent)
                     popDraft()
                 }
-                is SendMode.REPLY   -> {
+                is SendMode.REPLY -> {
                     state.sendMode.timelineEvent.let {
                         room.replyToMessage(it, action.text.toString(), action.autoMarkdown)
                         _viewEvents.post(RoomDetailViewEvents.MessageSent)
@@ -1441,7 +1443,7 @@ class RoomDetailViewModel @AssistedInject constructor(
     }
 
     override fun onPSTNSupportUpdated() {
-       updateShowDialerOptionState()
+        updateShowDialerOptionState()
     }
 
     private fun updateShowDialerOptionState() {

vector/src/main/java/im/vector/app/features/home/room/detail/ScrollOnNewMessageCallback.kt

@@ -19,7 +19,7 @@ package im.vector.app.features.home.room.detail
 import androidx.recyclerview.widget.LinearLayoutManager
 import im.vector.app.core.platform.DefaultListUpdateCallback
 import im.vector.app.features.home.room.detail.timeline.TimelineEventController
-import im.vector.app.features.home.room.detail.timeline.item.BaseEventItem
+import im.vector.app.features.home.room.detail.timeline.item.ItemWithEvents
 import timber.log.Timber
 import java.util.concurrent.CopyOnWriteArrayList
 
@@ -47,8 +47,8 @@ class ScrollOnNewMessageCallback(private val layoutManager: LinearLayoutManager,
         if (layoutManager.findFirstVisibleItemPosition() != position) {
             return
         }
-        val firstNewItem = timelineEventController.adapter.getModelAtPosition(position) as? BaseEventItem ?: return
+        val firstNewItem = timelineEventController.adapter.getModelAtPosition(position) as? ItemWithEvents ?: return
-        val firstNewItemIds = firstNewItem.getEventIds().firstOrNull()
+        val firstNewItemIds = firstNewItem.getEventIds().firstOrNull() ?: return
         val indexOfFirstNewItem = newTimelineEventIds.indexOf(firstNewItemIds)
         if (indexOfFirstNewItem != -1) {
             Timber.v("Should scroll to position: $position")

vector/src/main/java/im/vector/app/features/home/room/detail/timeline/TimelineEventController.kt

@@ -38,18 +38,15 @@ import im.vector.app.features.home.room.detail.timeline.factory.MergedHeaderItem
 import im.vector.app.features.home.room.detail.timeline.factory.TimelineItemFactory
 import im.vector.app.features.home.room.detail.timeline.helper.ContentDownloadStateTrackerBinder
 import im.vector.app.features.home.room.detail.timeline.helper.ContentUploadStateTrackerBinder
-import im.vector.app.features.home.room.detail.timeline.helper.ReadMarkerVisibilityStateChangedListener
+import im.vector.app.features.home.room.detail.timeline.helper.TimelineControllerInterceptorHelper
 import im.vector.app.features.home.room.detail.timeline.helper.TimelineEventDiffUtilCallback
 import im.vector.app.features.home.room.detail.timeline.helper.TimelineEventVisibilityStateChangedListener
 import im.vector.app.features.home.room.detail.timeline.helper.TimelineMediaSizeProvider
-import im.vector.app.features.home.room.detail.timeline.item.BaseEventItem
 import im.vector.app.features.home.room.detail.timeline.item.BasedMergedItem
-import im.vector.app.features.home.room.detail.timeline.item.CallTileTimelineItem
 import im.vector.app.features.home.room.detail.timeline.item.DaySeparatorItem
 import im.vector.app.features.home.room.detail.timeline.item.DaySeparatorItem_
 import im.vector.app.features.home.room.detail.timeline.item.MessageInformationData
 import im.vector.app.features.home.room.detail.timeline.item.ReadReceiptData
-import im.vector.app.features.home.room.detail.timeline.item.TimelineReadMarkerItem_
 import im.vector.app.features.home.room.detail.timeline.url.PreviewUrlRetriever
 import im.vector.app.features.media.ImageContentRenderer
 import im.vector.app.features.media.VideoContentRenderer
@@ -194,75 +191,20 @@ class TimelineEventController @Inject constructor(private val dateFormatter: Vec
         }
     }
 
+    private val interceptorHelper = TimelineControllerInterceptorHelper(
+            ::positionOfReadMarker,
+            adapterPositionMapping,
+            vectorPreferences,
+            callManager
+    )
+
     init {
         addInterceptor(this)
         requestModelBuild()
     }
 
-    // Update position when we are building new items
     override fun intercept(models: MutableList<EpoxyModel<*>>) = synchronized(modelCache) {
-        positionOfReadMarker = null
+        interceptorHelper.intercept(models, unreadState, timeline, callback)
-        adapterPositionMapping.clear()
-        val callIds = mutableSetOf<String>()
-        val modelsIterator = models.listIterator()
-        val showHiddenEvents = vectorPreferences.shouldShowHiddenEvents()
-        modelsIterator.withIndex().forEach {
-            val index = it.index
-            val epoxyModel = it.value
-            if (epoxyModel is CallTileTimelineItem) {
-                val callId = epoxyModel.attributes.callId
-                // We should remove the call tile if we already have one for this call or
-                // if this is an active call tile without an actual call (which can happen with permalink)
-                val shouldRemoveCallItem = callIds.contains(callId)
-                        || (!callManager.getAdvertisedCalls().contains(callId) && epoxyModel.attributes.callStatus.isActive())
-                if (shouldRemoveCallItem && !showHiddenEvents) {
-                    modelsIterator.remove()
-                    return@forEach
-                }
-                callIds.add(callId)
-            }
-            if (epoxyModel is BaseEventItem) {
-                epoxyModel.getEventIds().forEach { eventId ->
-                    adapterPositionMapping[eventId] = index
-                }
-            }
-        }
-        val currentUnreadState = this.unreadState
-        if (currentUnreadState is UnreadState.HasUnread) {
-            val position = adapterPositionMapping[currentUnreadState.firstUnreadEventId]?.plus(1)
-            positionOfReadMarker = position
-            if (position != null) {
-                val readMarker = TimelineReadMarkerItem_()
-                        .also {
-                            it.id("read_marker")
-                            it.setOnVisibilityStateChanged(ReadMarkerVisibilityStateChangedListener(callback))
-                        }
-                models.add(position, readMarker)
-            }
-        }
-        val shouldAddBackwardPrefetch = timeline?.hasMoreToLoad(Timeline.Direction.BACKWARDS) ?: false
-        if (shouldAddBackwardPrefetch) {
-            val indexOfPrefetchBackward = (previousModelsSize - 1)
-                    .coerceAtMost(models.size - DEFAULT_PREFETCH_THRESHOLD)
-                    .coerceAtLeast(0)
-
-            val loadingItem = LoadingItem_()
-                    .id("prefetch_backward_loading${System.currentTimeMillis()}")
-                    .showLoader(false)
-                    .setVisibilityStateChangedListener(Timeline.Direction.BACKWARDS)
-
-            models.add(indexOfPrefetchBackward, loadingItem)
-        }
-        val shouldAddForwardPrefetch = timeline?.hasMoreToLoad(Timeline.Direction.FORWARDS) ?: false
-        if (shouldAddForwardPrefetch) {
-            val indexOfPrefetchForward = DEFAULT_PREFETCH_THRESHOLD.coerceAtMost(models.size - 1)
-            val loadingItem = LoadingItem_()
-                    .id("prefetch_forward_loading${System.currentTimeMillis()}")
-                    .showLoader(false)
-                    .setVisibilityStateChangedListener(Timeline.Direction.FORWARDS)
-            models.add(indexOfPrefetchForward, loadingItem)
-        }
-        previousModelsSize = models.size
     }
 
     fun update(viewState: RoomDetailViewState) {
@@ -431,6 +373,14 @@ class TimelineEventController @Inject constructor(private val dateFormatter: Vec
         }
     }
 
+    private fun LoadingItem_.setVisibilityStateChangedListener(direction: Timeline.Direction): LoadingItem_ {
+        return onVisibilityStateChanged { _, _, visibilityState ->
+            if (visibilityState == VisibilityState.VISIBLE) {
+                callback?.onLoadMore(direction)
+            }
+        }
+    }
+
     private fun updateUTDStates(event: TimelineEvent, nextEvent: TimelineEvent?) {
         if (vectorPreferences.labShowCompleteHistoryInEncryptedRoom()) {
             return
@@ -461,14 +411,6 @@ class TimelineEventController @Inject constructor(private val dateFormatter: Vec
         return shouldAdd
     }
 
-    private fun LoadingItem_.setVisibilityStateChangedListener(direction: Timeline.Direction): LoadingItem_ {
-        return onVisibilityStateChanged { _, _, visibilityState ->
-            if (visibilityState == VisibilityState.VISIBLE) {
-                callback?.onLoadMore(direction)
-            }
-        }
-    }
-
     fun searchPositionOfEvent(eventId: String?): Int? = synchronized(modelCache) {
         return adapterPositionMapping[eventId]
     }

vector/src/main/java/im/vector/app/features/home/room/detail/timeline/factory/TimelineItemFactory.kt

@@ -16,7 +16,8 @@
 
 package im.vector.app.features.home.room.detail.timeline.factory
 
-import im.vector.app.core.epoxy.EmptyItem_
+import im.vector.app.core.epoxy.TimelineEmptyItem
+import im.vector.app.core.epoxy.TimelineEmptyItem_
 import im.vector.app.core.epoxy.VectorEpoxyModel
 import im.vector.app.core.resources.UserPreferencesProvider
 import im.vector.app.features.home.room.detail.timeline.TimelineEventController
@@ -114,6 +115,12 @@ class TimelineItemFactory @Inject constructor(private val messageItemFactory: Me
             Timber.e(throwable, "failed to create message item")
             defaultItemFactory.create(event, highlight, callback, throwable)
         }
-        return (computedModel ?: EmptyItem_())
+        return computedModel ?: buildEmptyItem(event)
+    }
+
+    private fun buildEmptyItem(timelineEvent: TimelineEvent): TimelineEmptyItem {
+        return TimelineEmptyItem_()
+                .id(timelineEvent.localId)
+                .eventId(timelineEvent.eventId)
     }
 }

vector/src/main/java/im/vector/app/features/home/room/detail/timeline/helper/TimelineControllerInterceptorHelper.kt

@@ -0,0 +1,151 @@
+/*
+ * Copyright (c) 2021 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package im.vector.app.features.home.room.detail.timeline.helper
+
+import com.airbnb.epoxy.EpoxyModel
+import com.airbnb.epoxy.VisibilityState
+import im.vector.app.core.epoxy.LoadingItem_
+import im.vector.app.core.epoxy.TimelineEmptyItem_
+import im.vector.app.features.call.webrtc.WebRtcCallManager
+import im.vector.app.features.home.room.detail.UnreadState
+import im.vector.app.features.home.room.detail.timeline.TimelineEventController
+import im.vector.app.features.home.room.detail.timeline.item.CallTileTimelineItem
+import im.vector.app.features.home.room.detail.timeline.item.ItemWithEvents
+import im.vector.app.features.home.room.detail.timeline.item.TimelineReadMarkerItem_
+import im.vector.app.features.settings.VectorPreferences
+import org.matrix.android.sdk.api.session.room.timeline.Timeline
+import kotlin.reflect.KMutableProperty0
+
+private const val DEFAULT_PREFETCH_THRESHOLD = 30
+
+class TimelineControllerInterceptorHelper(private val positionOfReadMarker: KMutableProperty0<Int?>,
+                                          private val adapterPositionMapping: MutableMap<String, Int>,
+                                          private val vectorPreferences: VectorPreferences,
+                                          private val callManager: WebRtcCallManager
+) {
+
+    private var previousModelsSize = 0
+
+    // Update position when we are building new items
+    fun intercept(
+            models: MutableList<EpoxyModel<*>>,
+            unreadState: UnreadState,
+            timeline: Timeline?,
+            callback: TimelineEventController.Callback?
+    ) {
+        positionOfReadMarker.set(null)
+        adapterPositionMapping.clear()
+        val callIds = mutableSetOf<String>()
+
+        // Add some prefetch loader if needed
+        models.addBackwardPrefetchIfNeeded(timeline, callback)
+        models.addForwardPrefetchIfNeeded(timeline, callback)
+
+        val modelsIterator = models.listIterator()
+        val showHiddenEvents = vectorPreferences.shouldShowHiddenEvents()
+        var index = 0
+        val firstUnreadEventId = (unreadState as? UnreadState.HasUnread)?.firstUnreadEventId
+        // Then iterate on models so we have the exact positions in the adapter
+        modelsIterator.forEach { epoxyModel ->
+            if (epoxyModel is ItemWithEvents) {
+                epoxyModel.getEventIds().forEach { eventId ->
+                    adapterPositionMapping[eventId] = index
+                    if (eventId == firstUnreadEventId) {
+                        modelsIterator.addReadMarkerItem(callback)
+                        index++
+                        positionOfReadMarker.set(index)
+                    }
+                }
+            }
+            if (epoxyModel is CallTileTimelineItem) {
+                modelsIterator.removeCallItemIfNeeded(epoxyModel, callIds, showHiddenEvents)
+            }
+            index++
+        }
+        previousModelsSize = models.size
+    }
+
+    private fun MutableListIterator<EpoxyModel<*>>.addReadMarkerItem(callback: TimelineEventController.Callback?) {
+        val readMarker = TimelineReadMarkerItem_()
+                .also {
+                    it.id("read_marker")
+                    it.setOnVisibilityStateChanged(ReadMarkerVisibilityStateChangedListener(callback))
+                }
+        add(readMarker)
+        // Use next as we still have some process to do before the next iterator loop
+        next()
+    }
+
+    private fun MutableListIterator<EpoxyModel<*>>.removeCallItemIfNeeded(
+            epoxyModel: CallTileTimelineItem,
+            callIds: MutableSet<String>,
+            showHiddenEvents: Boolean
+    ) {
+        val callId = epoxyModel.attributes.callId
+        // We should remove the call tile if we already have one for this call or
+        // if this is an active call tile without an actual call (which can happen with permalink)
+        val shouldRemoveCallItem = callIds.contains(callId)
+                || (!callManager.getAdvertisedCalls().contains(callId) && epoxyModel.attributes.callStatus.isActive())
+        if (shouldRemoveCallItem && !showHiddenEvents) {
+            remove()
+            val emptyItem = TimelineEmptyItem_()
+                    .id(epoxyModel.id())
+                    .eventId(epoxyModel.attributes.informationData.eventId)
+            add(emptyItem)
+        }
+        callIds.add(callId)
+    }
+
+    private fun MutableList<EpoxyModel<*>>.addBackwardPrefetchIfNeeded(timeline: Timeline?, callback: TimelineEventController.Callback?) {
+        val shouldAddBackwardPrefetch = timeline?.hasMoreToLoad(Timeline.Direction.BACKWARDS) ?: false
+        if (shouldAddBackwardPrefetch) {
+            val indexOfPrefetchBackward = (previousModelsSize - 1)
+                    .coerceAtMost(size - DEFAULT_PREFETCH_THRESHOLD)
+                    .coerceAtLeast(0)
+
+            val loadingItem = LoadingItem_()
+                    .id("prefetch_backward_loading${System.currentTimeMillis()}")
+                    .showLoader(false)
+                    .setVisibilityStateChangedListener(Timeline.Direction.BACKWARDS, callback)
+
+            add(indexOfPrefetchBackward, loadingItem)
+        }
+    }
+
+    private fun MutableList<EpoxyModel<*>>.addForwardPrefetchIfNeeded(timeline: Timeline?, callback: TimelineEventController.Callback?) {
+        val shouldAddForwardPrefetch = timeline?.hasMoreToLoad(Timeline.Direction.FORWARDS) ?: false
+        if (shouldAddForwardPrefetch) {
+            val indexOfPrefetchForward = DEFAULT_PREFETCH_THRESHOLD.coerceAtMost(size - 1)
+            val loadingItem = LoadingItem_()
+                    .id("prefetch_forward_loading${System.currentTimeMillis()}")
+                    .showLoader(false)
+                    .setVisibilityStateChangedListener(Timeline.Direction.FORWARDS, callback)
+            add(indexOfPrefetchForward, loadingItem)
+        }
+    }
+
+    private fun LoadingItem_.setVisibilityStateChangedListener(
+            direction: Timeline.Direction,
+            callback: TimelineEventController.Callback?
+    ): LoadingItem_ {
+        return onVisibilityStateChanged { _, _, visibilityState ->
+            if (visibilityState == VisibilityState.VISIBLE) {
+                callback?.onLoadMore(direction)
+            }
+        }
+    }
+}

vector/src/main/java/im/vector/app/features/home/room/detail/timeline/item/BaseEventItem.kt

@@ -32,7 +32,7 @@ import im.vector.app.core.utils.DimensionConverter
 /**
  * Children must override getViewType()
  */
-abstract class BaseEventItem<H : BaseEventItem.BaseHolder> : VectorEpoxyModel<H>() {
+abstract class BaseEventItem<H : BaseEventItem.BaseHolder> : VectorEpoxyModel<H>(), ItemWithEvents {
 
     // To use for instance when opening a permalink with an eventId
     @EpoxyAttribute
@@ -53,12 +53,6 @@ abstract class BaseEventItem<H : BaseEventItem.BaseHolder> : VectorEpoxyModel<H>
         holder.checkableBackground.isChecked = highlighted
     }
 
-    /**
-     * Returns the eventIds associated with the EventItem.
-     * Will generally get only one, but it handles the merging items.
-     */
-    abstract fun getEventIds(): List<String>
-
     abstract class BaseHolder(@IdRes val stubId: Int) : VectorEpoxyHolder() {
         val leftGuideline by bind<View>(R.id.messageStartGuideline)
         val checkableBackground by bind<CheckableView>(R.id.messageSelectedBackground)

vector/src/main/java/im/vector/app/features/home/room/detail/timeline/item/ItemWithEvents.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2019 New Vector Ltd
+ * Copyright (c) 2021 New Vector Ltd
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-package im.vector.app.core.epoxy
+package im.vector.app.features.home.room.detail.timeline.item
 
-import com.airbnb.epoxy.EpoxyModelClass
+interface ItemWithEvents {
-import im.vector.app.R
+    /**
-
+     * Returns the eventIds associated with the EventItem.
-@EpoxyModelClass(layout = R.layout.item_empty)
+     * Will generally get only one, but it handles the merged items.
-abstract class EmptyItem : VectorEpoxyModel<EmptyItem.Holder>() {
+     */
-    class Holder : VectorEpoxyHolder()
+    fun getEventIds(): List<String>
 }