Avoid multiple notifications

app/src/main/java/app/fedilab/android/mastodon/helper/NotificationsHelper.java

@@ -62,6 +62,7 @@ import retrofit2.converter.gson.GsonConverterFactory;
 public class NotificationsHelper {
 
     public static HashMap<String, String> since_ids = new HashMap<>();
+    public static HashMap<String, List<String>> pushed_notifications = new HashMap<>();
 
     public static synchronized void task(Context context, String slug) throws DBException {
 
@@ -184,6 +185,19 @@ public class NotificationsHelper {
         //No previous notifications in cache, so no notification will be sent
 
         for (Notification notification : notifications) {
+            List<String> notificationIDList;
+            if (pushed_notifications.containsKey(key)) {
+                notificationIDList = pushed_notifications.get(key);
+                if (notificationIDList != null && notificationIDList.contains(notification.id)) {
+                    continue;
+                }
+            }
+            notificationIDList = pushed_notifications.get(key);
+            if (notificationIDList == null) {
+                notificationIDList = new ArrayList<>();
+            }
+            notificationIDList.add(notification.id);
+            pushed_notifications.put(key, notificationIDList);
             String notificationUrl;
             String title = null;
             String message = null;