Cancel sending events when removing local echoes

TODO.md

@@ -1,6 +1,5 @@
 # TODO
 
-- redact local echo effect
 - being able to redact local echos
 - unselect before unfocusing
 

src/backend/matrix_client.py

@@ -118,6 +118,7 @@ class MatrixClient(nio.AsyncClient):
 
         self.upload_monitors:    Dict[UUID, nio.TransferMonitor] = {}
         self.upload_tasks:       Dict[UUID, asyncio.Task]        = {}
+        self.send_message_tasks: Dict[UUID, asyncio.Task]        = {}
 
         self.first_sync_done: asyncio.Event      = asyncio.Event()
         self.first_sync_date: Optional[datetime] = None
@@ -342,7 +343,7 @@ class MatrixClient(nio.AsyncClient):
             room_id, tx_id, event_type, content=echo_body, mentions=mentions,
         )
 
-        await self._send_message(room_id, content)
+        await self._send_message(room_id, content, tx_id)
 
 
     async def toggle_pause_upload(
@@ -592,7 +593,7 @@ class MatrixClient(nio.AsyncClient):
                 content["info"].get("thumbnail_info", {}).get("mimetype", ""),
         )
 
-        await self._send_message(room_id, content)
+        await self._send_message(room_id, content, transaction_id)
 
 
     async def _local_echo(
@@ -648,9 +649,14 @@ class MatrixClient(nio.AsyncClient):
         await self.set_room_last_event(room_id, event)
 
 
-    async def _send_message(self, room_id: str, content: dict) -> None:
+    async def _send_message(
+        self, room_id: str, content: dict, transaction_id: UUID,
+    ) -> None:
         """Send a message event with `content` dict to a room."""
 
+        self.send_message_tasks[transaction_id] = \
+            asyncio.current_task()  # type: ignore
+
         async with self.backend.send_locks[room_id]:
             await self.room_send(
                 room_id                   = room_id,
@@ -915,6 +921,13 @@ class MatrixClient(nio.AsyncClient):
                 if not event:
                     continue
 
+                if event.is_local_echo:
+                    if user_id == self.user_id:
+                        uuid = UUID(event.id.replace("echo-", ""))
+                        self.send_message_tasks[uuid].cancel()
+
+                    event.is_local_echo = False
+                else:
                     if user_id == self.user_id:
                         tasks.append(
                             self.room_redact(room_id, event.event_id, reason),