streams: Handle adding new stream events.

Author: Abhirup-99

zulipterminal/model.py

@@ -53,7 +53,8 @@
     'stream_id': int,
     'stream_ids': List[int],  # NOTE: replaces 'stream_id' in ZFL 35 for peer*
     'value': bool,
-    'message_ids': List[int]  # Present when subject of msg(s) is updated
+    'message_ids': List[int],  # Present when subject of msg(s) is updated,
+    'subscriptions': List[Dict[str, Any]]
 }, total=False)  # Each Event will only have a subset of these
 
 EditPropagateMode = Literal['change_one', 'change_all', 'change_later']
@@ -785,6 +786,21 @@ def get_stream_by_id(streams: List[StreamData], stream_id: int
                     sort_streams(self.pinned_streams)
                     self.controller.view.left_panel.update_stream_view()
                     self.controller.update_screen()
+        elif event['op'] == 'add':
+            def make_reduced_stream_data(stream: Any) -> StreamData:
+                # stream_id has been changed to id.
+                return StreamData({'name': stream['name'],
+                                   'id': stream['stream_id'],
+                                   'color': stream['color'],
+                                   'invite_only': stream['invite_only'],
+                                   'description': stream['description']})
+
+            subscription = event['subscriptions'][0]
+            stream_data = make_reduced_stream_data(subscription)
+            self.stream_dict[subscription['stream_id']] = stream_data
+            self.pinned_streams.append(stream_data)
+            self.controller.update_screen()
+
         elif event['op'] in ('peer_add', 'peer_remove'):
             # NOTE: ZFL 35 commit was not atomic with API change
             #       (ZFL >=35 can use new plural style)