fix #650 notifications alerting multiple times

app/src/main/java/com/keylesspalace/tusky/NotificationPullJobCreator.java

@@ -114,6 +114,7 @@ public final class NotificationPullJobCreator implements JobCreator {
             Collections.reverse(notificationList);
             BigInteger newId = new BigInteger(account.getLastNotificationId());
             BigInteger newestId = BigInteger.ZERO;
+            boolean isFirstOfBatch = true;
 
             for (Notification notification : notificationList) {
                 BigInteger currentId = new BigInteger(notification.getId());
@@ -122,7 +123,8 @@ public final class NotificationPullJobCreator implements JobCreator {
                 }
 
                 if (isBiggerThan(currentId, newId)) {
-                    NotificationHelper.make(context, notification, account);
+                    NotificationHelper.make(context, notification, account, isFirstOfBatch);
+                    isFirstOfBatch = false;
                 }
             }
 

app/src/main/java/com/keylesspalace/tusky/util/NotificationHelper.java

@@ -112,7 +112,7 @@ public class NotificationHelper {
      * @param account the account for which the notification should be shown
      */
 
-    public static void make(final Context context, Notification body, AccountEntity account) {
+    public static void make(final Context context, Notification body, AccountEntity account, boolean isFirstOfBatch) {
 
         if (!filterNotification(account, body, context)) {
             return;
@@ -203,6 +203,11 @@ public class NotificationHelper {
         builder.setCategory(NotificationCompat.CATEGORY_SOCIAL);
         builder.setOnlyAlertOnce(true);
 
+        // only alert for the first notification of a batch to avoid multiple alerts at once
+        if(!isFirstOfBatch) {
+            builder.setGroupAlertBehavior(NotificationCompat.GROUP_ALERT_SUMMARY);
+        }
+
         // Summary
         // =======
         final NotificationCompat.Builder summaryBuilder = newNotification(context, body, account, true);