model: Add footer notification for messages.

This will set a footer text notifying the user everytime
he sends or edits a message that is outside the current
narrow. This will give the user a pointer as to why the
message disappeared from the screen.

Fixes zulip#781.

zulipterminal/model.py

@@ -230,6 +230,7 @@ def unset_search_narrow(self) -> None:
     def get_message_ids_in_current_narrow(self) -> Set[int]:
         narrow = self.narrow
         index = self.index
+        print(narrow, flush=True)
         if narrow == []:
             ids = index['all_msg_ids']
         elif self.is_search_narrow():  # Check searches first
@@ -879,6 +880,7 @@ def _handle_message_event(self, event: Event) -> None:
         Handle new messages (eg. add message to the end of the view)
         """
         message = event['message']
+        print(event, flush=True)
         # sometimes `flags` are missing in `event` so initialize
         # an empty list of flags in that case.
         message['flags'] = event.get('flags', [])
@@ -966,6 +968,10 @@ def _handle_message_event(self, event: Event) -> None:
                              and self.narrow[1][1] == message['subject']))):
                     msg_log.append(msg_w)
 
+                if not append_to_stream:
+                    self.controller.view.set_footer_text(
+                        'Message sent outside of current narrow', 3)
+
             elif (message['type'] == 'private' and len(self.narrow) == 1
                     and self.narrow[0][0] == "pm_with"):
                 narrow_recipients = self.recipients
@@ -1001,6 +1007,7 @@ def _handle_update_message_event(self, event: Event) -> None:
         # If the message is indexed
         if self.index['messages'].get(message_id):
             message = self.index['messages'][message_id]
+            print("message =>", message, flush=True)
             self.index['edited_messages'].add(message_id)
 
             if 'rendered_content' in event:
@@ -1011,11 +1018,21 @@ def _handle_update_message_event(self, event: Event) -> None:
             # 'subject' is not present in update event if
             # the event didn't have a 'subject' update.
             if 'subject' in event:
+                old_subject = self.index['messages'][message_id]['subject']
                 new_subject = event['subject']
+                print("old subject =>", old_subject, flush=True)
+                print("new subject =>", new_subject, flush=True)
                 for msg_id in event['message_ids']:
                     self.index['messages'][msg_id]['subject'] = new_subject
                     self._update_rendered_view(msg_id)
 
+                view = self.controller.view
+                print("event=>", event, flush=True)
+                if (len(self.narrow) == 2
+                    and self.narrow[1][0] == 'topic'
+                        and old_subject != new_subject):
+                    view.set_footer_text("Subject changed", 3)
+
     def _handle_reaction_event(self, event: Event) -> None:
         """
         Handle change to reactions on a message