Add total unread notification count to home screen (#7891)

* Add total unread notification count to home screen

This will be calculated on each sync heartbeat (for now, using the state updates for the room list service).

* Simplify `counter` parameter logic

* Read the total unread count when the home screen is first displayed

---------

Co-authored-by: Benoit Marty <benoitm@element.io>

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/MatrixClient.kt

@@ -505,6 +505,12 @@ interface MatrixClient : ClientUrlContentFetcher {
 
     /** Returns a provider for the capabilities the homeserver advertises, such as whether the display name can be changed. */
     fun homeserverCapabilities(): HomeserverCapabilitiesProvider
+
+    /**
+     * Returns the total number of unread notifications across all rooms, as currently known by the client.
+     * This is a snapshot and may be out of date if the sync is running.
+     */
+    fun totalUnreadCount(): Result<Long>
 }
 
 /**

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/sync/SyncService.kt

@@ -8,6 +8,7 @@
 
 package io.element.android.libraries.matrix.api.sync
 
+import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.StateFlow
 
 /**
@@ -37,4 +38,10 @@ interface SyncService {
      * This is `false` only while the state is [SyncState.Offline]; an idle or errored sync still counts as online.
      */
     val isOnline: StateFlow<Boolean>
+
+    /**
+     * Flow that will emit every time the sync has received a response from the server, even if it was empty.
+     * Useful for triggering UI updates when the sync is running.
+     */
+    val heartBeat: Flow<Unit>
 }