Admin API endpoint to delete a reported event (#15116)

* Admin api to delete event report

* lint +  tests

* newsfile

* Apply suggestions from code review

Co-authored-by: David Robertson <david.m.robertson1@gmail.com>

* revert changes - move to WorkerStore

* update unit test

* Note that timestamp is in millseconds

---------

Co-authored-by: David Robertson <david.m.robertson1@gmail.com>

synapse/storage/databases/main/room.py

@@ -1417,6 +1417,27 @@ class RoomWorkerStore(CacheInvalidationWorkerStore):
             get_un_partial_stated_rooms_from_stream_txn,
         )
 
+    async def delete_event_report(self, report_id: int) -> bool:
+        """Remove an event report from database.
+
+        Args:
+            report_id: Report to delete
+
+        Returns:
+            Whether the report was successfully deleted or not.
+        """
+        try:
+            await self.db_pool.simple_delete_one(
+                table="event_reports",
+                keyvalues={"id": report_id},
+                desc="delete_event_report",
+            )
+        except StoreError:
+            # Deletion failed because report does not exist
+            return False
+
+        return True
+
 
 class _BackgroundUpdates:
     REMOVE_TOMESTONED_ROOMS_BG_UPDATE = "remove_tombstoned_rooms_from_directory"
@@ -2139,7 +2160,19 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
         reason: Optional[str],
         content: JsonDict,
         received_ts: int,
-    ) -> None:
+    ) -> int:
+        """Add an event report
+
+        Args:
+            room_id: Room that contains the reported event.
+            event_id: The reported event.
+            user_id: User who reports the event.
+            reason: Description that the user specifies.
+            content: Report request body (score and reason).
+            received_ts: Time when the user submitted the report (milliseconds).
+        Returns:
+            Id of the event report.
+        """
         next_id = self._event_reports_id_gen.get_next()
         await self.db_pool.simple_insert(
             table="event_reports",
@@ -2154,6 +2187,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
             },
             desc="add_event_report",
         )
+        return next_id
 
     async def get_event_report(self, report_id: int) -> Optional[Dict[str, Any]]:
         """Retrieve an event report