model/api_types: Handle add/remove subscription events.

This commit adds event handling code for newly added/removed
subscriptions. To store the stream subscriptions which are being updated
in the event, a new field named "subscriptions" is added to the
SubscriptionEvent class.

Co-authored-by: Abhirup Pal <abhiruppalmethodist@gmail.com>
Co-authored-by: Vishwesh Pillai <vishwesh103@gmail.com>

Author: theViz343

zulipterminal/api_types.py

@@ -438,6 +438,18 @@ class SubscriptionPeerAddRemoveEvent(TypedDict):
     user_ids: List[int]  # NOTE: replaces 'user_id' in ZFL 35
 
 
+class SubscriptionAddEvent(TypedDict):
+    type: Literal["subscription"]
+    op: Literal["add"]
+    subscriptions: List[Subscription]
+
+
+class SubscriptionRemoveEvent(TypedDict):
+    type: Literal["subscription"]
+    op: Literal["remove"]
+    subscriptions: List[RemovedSubscription]
+
+
 # -----------------------------------------------------------------------------
 # See https://zulip.com/api/get-events#typing-start and -stop
 class _TypingEventUser(TypedDict):
@@ -532,6 +544,8 @@ class UpdateDisplaySettingsEvent(TypedDict):
     UpdateMessagesLocationEvent,
     ReactionEvent,
     SubscriptionUpdateEvent,
+    SubscriptionAddEvent,
+    SubscriptionRemoveEvent,
     SubscriptionPeerAddRemoveEvent,
     TypingEvent,
     UpdateMessageFlagsEvent,

zulipterminal/model.py

@@ -1482,7 +1482,7 @@ def get_stream_by_id(streams: List[StreamData], stream_id: int) -> StreamData:
                         self.visual_notified_streams.add(stream_id)
                     else:
                         self.visual_notified_streams.discard(stream_id)
-        elif event["op"] in ("peer_add", "peer_remove"):
+        elif event["op"] == "peer_add" or event["op"] == "peer_remove":
             # NOTE: ZFL 35 commit was not atomic with API change
             #       (ZFL >=35 can use new plural style)
             if "stream_ids" not in event or "user_ids" not in event:
@@ -1500,6 +1500,18 @@ def get_stream_by_id(streams: List[StreamData], stream_id: int) -> StreamData:
                     else:
                         for user_id in user_ids:
                             subscribers.remove(user_id)
+        elif event["op"] == "add":
+            self._subscribe_to_streams(event["subscriptions"])
+            # print(event["subscriptions"])
+            self.normalize_and_cache_message_retention_text()
+            self.normalize_date_created_field()
+
+            self.controller.view.left_panel.update_stream_view()
+            self.controller.update_screen()
+        elif event["op"] == "remove":
+            self._unsubscribe_from_streams(event["subscriptions"])
+            self.controller.view.left_panel.update_stream_view()
+            self.controller.update_screen()
 
     def _handle_typing_event(self, event: Event) -> None:
         """