Save the a copy of the notification marker ID locally (#3672)

Not all servers support the marker API. If they don't the user will
potentially get duplicate Android notifications.

To resolve this, store a copy of the notification marker ID locally as
well. Defer to the remote marker if it exists (and is newer than the
local marker).

Fixes https://github.com/tuskyapp/Tusky/issues/3671

app/src/main/java/com/keylesspalace/tusky/components/notifications/NotificationFetcher.kt

@@ -102,11 +102,13 @@ class NotificationFetcher @Inject constructor(
      * Here, "new" means "notifications with IDs newer than notifications the user has already
      * seen."
      *
-     * The "water mark" for Mastodon Notification IDs are stored in two places.
+     * The "water mark" for Mastodon Notification IDs are stored in three places.
      *
      * - acccount.lastNotificationId -- the ID of the top-most notification when the user last
      *   left the Notifications tab.
      * - The Mastodon "marker" API -- the ID of the most recent notification fetched here.
+     * - account.notificationMarkerId -- local version of the value from the Mastodon marker
+     *   API, in case the Mastodon server does not implement that API.
      *
      * The user may have refreshed the "Notifications" tab and seen notifications newer than the
      * ones that were last fetched here. So `lastNotificationId` takes precedence if it is greater
@@ -115,11 +117,21 @@ class NotificationFetcher @Inject constructor(
     private fun fetchNewNotifications(account: AccountEntity): List<Notification> {
         val authHeader = String.format("Bearer %s", account.accessToken)
 
+        // Figure out where to read from. Choose the most recent notification ID from:
+        //
+        // - The Mastodon marker API (if the server supports it)
+        // - account.notificationMarkerId
+        // - account.lastNotificationId
         Log.d(TAG, "getting notification marker for ${account.fullName}")
-        val minId = when (val marker = fetchMarker(authHeader, account)) {
-            null -> account.lastNotificationId.takeIf { it != "0" }
-            else -> if (account.lastNotificationId.isLessThan(marker.lastReadId)) marker.lastReadId else account.lastNotificationId
-        }
+        val remoteMarkerId = fetchMarker(authHeader, account)?.lastReadId ?: "0"
+        val localMarkerId = account.notificationMarkerId
+        val markerId = if (remoteMarkerId.isLessThan(localMarkerId)) localMarkerId else remoteMarkerId
+        val readingPosition = account.lastNotificationId
+
+        val minId = if (readingPosition.isLessThan(markerId)) markerId else readingPosition
+        Log.d(TAG, "  remoteMarkerId: $remoteMarkerId")
+        Log.d(TAG, "  localMarkerId: $localMarkerId")
+        Log.d(TAG, "  readingPosition: $readingPosition")
 
         Log.d(TAG, "getting Notifications for ${account.fullName}, min_id: $minId")
 
@@ -139,6 +151,8 @@ class NotificationFetcher @Inject constructor(
                 domain = account.domain,
                 notificationsLastReadId = newMarkerId
             )
+            account.notificationMarkerId = newMarkerId
+            accountManager.saveAccount(account)
         }
 
         return notifications

app/src/main/java/com/keylesspalace/tusky/db/AccountEntity.kt

@@ -15,6 +15,7 @@
 
 package com.keylesspalace.tusky.db
 
+import androidx.room.ColumnInfo
 import androidx.room.Entity
 import androidx.room.Index
 import androidx.room.PrimaryKey
@@ -70,7 +71,19 @@ data class AccountEntity(
      * that media previews are shown as well as downloaded.
      */
     var mediaPreviewEnabled: Boolean = true,
+    /**
+     * ID of the last notification the user read on the Notification, list, and should be restored
+     * to view when the user returns to the list.
+     *
+     * May not be the ID of the most recent notification if the user has scrolled down the list.
+     */
     var lastNotificationId: String = "0",
+    /**
+     *  ID of the most recent Mastodon notification that Tusky has fetched to show as an
+     *  Android notification.
+     */
+    @ColumnInfo(defaultValue = "0")
+    var notificationMarkerId: String = "0",
     var emojis: List<Emoji> = emptyList(),
     var tabPreferences: List<TabData> = defaultTabs(),
     var notificationsFilter: String = "[\"follow_request\"]",

app/src/main/java/com/keylesspalace/tusky/db/AppDatabase.java

@@ -41,10 +41,11 @@ import java.io.File;
         TimelineAccountEntity.class,
         ConversationEntity.class
     },
-    version = 50,
+    version = 51,
     autoMigrations = {
         @AutoMigration(from = 48, to = 49),
-        @AutoMigration(from = 49, to = 50, spec = AppDatabase.MIGRATION_49_50.class)
+        @AutoMigration(from = 49, to = 50, spec = AppDatabase.MIGRATION_49_50.class),
+        @AutoMigration(from = 50, to = 51)
     }
 )
 public abstract class AppDatabase extends RoomDatabase {