boxes: Add class method in MessageBox to update content header.

This commit adds a method to update content header of a specific message
box (if required).

The current logic re-builds the whole message box if an update is required.
This might need improvement as to update a specific element only. (Though
that might prove useful only if that element is rendered via a dedicated
class method).

Tests added.

Author: Ezio-Sarthak

tests/ui/test_ui_tools.py

@@ -1877,6 +1877,41 @@ def test_main_view_generates_EDITED_label(self, mocker,
             assert label[0].text == 'EDITED'
             assert label[1][1] == 7
 
+    @pytest.mark.parametrize('message', [
+        {
+            'id': 4,
+            'type': 'stream',
+            'display_recipient': 'Verona',
+            'stream_id': 5,
+            'subject': 'Test topic',
+            'is_me_message': True,
+            'flags': [],
+            'content': '',
+            'reactions': [],
+            'sender_full_name': 'Human 1',  # this message name
+            'timestamp': 1532103879,
+        }
+    ])
+    @pytest.mark.parametrize('differences, header_needed, update_required', [
+        ({'subject': 'Test topic 2'}, True, True),
+        ({}, False, False),
+        ({'sender_full_name': 'Human 2'}, False, True),
+        ({'timestamp': 1532103869}, False, False),
+    ], ids=[
+        'recipient_header_present',
+        'recipient_header_not_present',
+        'content_header_present',
+        'content_header_not_present',
+    ])
+    def test_update_msg_content_header(self, msg_box, message,
+                                       update_required, mocker,
+                                       differences, header_needed):
+        last_msg = dict(message, **differences)
+
+        msg_box = MessageBox(message, self.model, last_msg)
+
+        assert msg_box.update_msg_content_header() == update_required
+
     @pytest.mark.parametrize('key', keys_for_command('STREAM_MESSAGE'))
     @pytest.mark.parametrize('narrow, expect_to_prefill', [
         ([], False),

zulipterminal/ui_tools/boxes.py

@@ -1294,6 +1294,26 @@ def main_view(self) -> List[Any]:
         ]
         return [part for part, condition in parts if condition]
 
+    def update_msg_content_header(self) -> bool:
+        """
+        Update the content header of a message box (if required).
+        """
+        update_required = False
+
+        if self.need_recipient_header():
+            update_required = (self[1][1].text != ' ')
+
+        # Content header is not None
+        elif isinstance(self[0][1], urwid.Text):
+            update_required = (self[0][1].text != ' ')
+
+        if update_required:
+            # Re initialize the message if update is required.
+            # FIXME: Render specific element (here content header) instead?
+            super().__init__(self.main_view())
+
+        return update_required
+
     @classmethod
     def transform_content(cls, content: Any, server_url: str,
                           ) -> Tuple[Tuple[None, Any],