Prevent duplicate notifications for the same event

src/backend/backend.py

@@ -9,7 +9,7 @@ import time
 import traceback
 from datetime import datetime
 from pathlib import Path
-from typing import Any, DefaultDict, Dict, List, Optional, Tuple, Union
+from typing import Any, DefaultDict, Dict, List, Optional, Set, Tuple, Union
 from urllib.parse import urlparse
 
 import aiohttp
@@ -134,7 +134,8 @@ class Backend:
 
         self.mxc_events: DefaultDict[str, List[Event]] = DefaultDict(list)
 
-        self.notification_avatar_cache: Dict[str, Path] = {}  # {mxc: path}
+        self.notified_events:           Set[str]        = set()  # {event_id}
+        self.notification_avatar_cache: Dict[str, Path] = {}     # {mxc: path}
 
 
     def __repr__(self) -> str:

src/backend/matrix_client.py

@@ -2181,12 +2181,16 @@ class MatrixClient(nio.AsyncClient):
         if from_us:
             return item
 
-        if await self.event_is_past(ev):
+        already_notified = item.event_id in self.backend.notified_events
+
+        if already_notified or await self.event_is_past(ev):
             await self.update_account_unread_counts()
             return item
 
         # Alerts & notifications
 
+        self.backend.notified_events.add(item.event_id)
+
         room_item = self.models[self.user_id, "rooms"][room.room_id]
 
         unread = \