Add ignoring invite sender & fix forgotten rooms

When declining an invite, the popup now offers a checkbox to also add
the sender to the account data m.ignored_user_list event.

This will hide any further invite or message from that user in syncs,
and also immediatly remove the ones we currently have.

As a side-effect, the long-time bug that caused forgotten rooms to
immediatly reappear due to received a "<user> left" event has been
fixed.

src/backend/matrix_client.py

@@ -210,6 +210,7 @@ class MatrixClient(nio.AsyncClient):
         self.fully_loaded_rooms:   Set[str]       = set()  # {room_id}
         self.loaded_once_rooms:    Set[str]       = set()  # {room_id}
         self.cleared_events_rooms: Set[str]       = set()  # {room_id}
+        self.ignored_rooms:        Set[str]       = set()  # {room_id}
 
         self.event_to_echo_ids: Dict[str, str] = {}
 
@@ -220,7 +221,8 @@ class MatrixClient(nio.AsyncClient):
         self.unassigned_event_last_read_by: DefaultDict[str, Dict[str, int]] =\
             DefaultDict(dict)
 
-        self.push_rules: nio.PushRulesEvent = nio.PushRulesEvent()
+        self.push_rules:       nio.PushRulesEvent = nio.PushRulesEvent()
+        self.ignored_user_ids: Set[str]           = set()
 
         # {room_id: event}
         self.power_level_events: Dict[str, nio.PowerLevelsEvent] = {}
@@ -523,6 +525,51 @@ class MatrixClient(nio.AsyncClient):
             await asyncio.sleep(0.2)
 
 
+    async def ignore_user(self, user_id: str, ignore: bool) -> None:
+        ignored = self.ignored_user_ids.copy()
+
+        if ignore:
+            ignored.add(user_id)
+        else:
+            ignored.discard(user_id)
+
+        path   = ["user", self.user_id, "account_data", "m.ignored_user_list"]
+        params = {"access_token": self.access_token}
+
+        await self._send(
+            nio.responses.EmptyResponse,
+            "PUT",
+            nio.Api._build_path(path, params),
+            nio.Api.to_json({"ignored_users": {u: {} for u in ignored}}),
+        )
+
+        if not ignore:
+            return
+
+        # Invites and messages from ignored users won't be returned anymore on
+        # syncs, thus will be absent on client restart. Clean up immediatly:
+
+        room_model = self.models[self.user_id, "rooms"]
+
+        with room_model.batch_remove():
+            for room_id, room in room_model.copy().items():
+                if room.inviter_id == user_id:
+                    self.ignored_rooms.add(room_id)
+                    del room_model[room_id]
+                    self.models.pop((self.user_id, room_id, "events"), None)
+                    self.models.pop((self.user_id, room_id, "members"), None)
+                    continue
+
+                event_model = self.models[self.user_id, room_id, "events"]
+
+                with event_model.batch_remove():
+                    for event_id, event in event_model.copy().items():
+                        if event.sender_id == user_id:
+                            del event_model[event_id]
+
+        await self.update_account_unread_counts()
+
+
     async def can_kick(self, room_id: str, target_user_id: str) -> bool:
         """Return whether we can kick a certain user in a room."""
 
@@ -1172,6 +1219,7 @@ class MatrixClient(nio.AsyncClient):
         will be marked as suitable for destruction by the server.
         """
 
+        self.ignored_rooms.add(room_id)
         self.models[self.user_id, "rooms"].pop(room_id, None)
         self.models.pop((self.user_id, room_id, "events"), None)
         self.models.pop((self.user_id, room_id, "members"), None)
@@ -2057,6 +2105,8 @@ class MatrixClient(nio.AsyncClient):
     ) -> None:
         """Register/update a `nio.MatrixRoom` as a `models.items.Room`."""
 
+        self.ignored_rooms.discard(room.room_id)
+
         inviter        = getattr(room, "inviter", "") or ""
         levels         = room.power_levels
         can_send_state = partial(levels.can_user_send_state, self.user_id)