boxes/helper: Support typeahead for topic name in recipient box.

Note that this does not work correctly when the search text includes
whitespaces, due to lack of urwid-readline support.

Test added.

Author: kaustubh-nair

tests/conftest.py

@@ -331,6 +331,11 @@ def zulip_version(request):
     return request.param
 
 
+@pytest.fixture
+def topics():
+    return ['Topic 1', 'This is a topic', 'Hello there!']
+
+
 @pytest.fixture
 def initial_data(logged_on_user, users_fixture, streams_fixture):
     """

tests/ui_tools/test_boxes.py

@@ -298,6 +298,44 @@ def test__stream_box_autocomplete_with_spaces(self, mocker, write_box,
 
         assert write_box.contents[0][0][0].edit_text == expected_text
 
+    @pytest.mark.parametrize(['text', 'matching_topics'], [
+        ('', ['Topic 1', 'This is a topic', 'Hello there!']),
+        ('Th', ['This is a topic']),
+    ], ids=[
+        'no_search_text',
+        'single_word_search_text',
+    ])
+    def test__topic_box_autocomplete(self, mocker, write_box, text, topics,
+                                     matching_topics, state=1):
+        write_box.model.topics_in_stream.return_value = topics
+        _process_typeaheads = mocker.patch(BOXES
+                                           + '.WriteBox._process_typeaheads')
+
+        write_box._topic_box_autocomplete(text, state)
+
+        _process_typeaheads.assert_called_once_with(matching_topics, state,
+                                                    matching_topics)
+
+    @pytest.mark.parametrize('text, expected_text', [
+        ('Th', 'This is a topic'),
+        pytest.param('This i', 'This is a topic', marks=pytest.mark.xfail(
+                             reason="Lacking urwid-readline support")),
+    ])
+    def test__topic_box_autocomplete_with_spaces(self, mocker, write_box,
+                                                 text, expected_text,
+                                                 topics):
+        write_box.stream_box_view(1000)
+        write_box.model.topics_in_stream.return_value = topics
+        write_box.contents[0][0][1].set_edit_text(text)
+        write_box.contents[0][0][1].set_edit_pos(len(text))
+        write_box.focus_position = 0
+        write_box.contents[0][0].focus_col = 1
+        size = (20,)
+
+        write_box.keypress(size, keys_for_command('AUTOCOMPLETE').pop())
+
+        assert write_box.contents[0][0][1].edit_text == expected_text
+
     @pytest.mark.parametrize(['suggestions', 'state', 'expected_state',
                               'expected_typeahead', 'is_truncated'], [
       (['zero', 'one', 'two'], 1, 1, '*one*', False),

zulipterminal/helper.py

@@ -487,6 +487,11 @@ def match_emoji(emoji: str, text: str) -> bool:
     return emoji.lower().startswith(text.lower())
 
 
+def match_topics(topic_names: List[str], search_text: str) -> List[str]:
+    return [name for name in topic_names
+            if name.lower().startswith(search_text.lower())]
+
+
 DataT = TypeVar('DataT')
 
 

zulipterminal/ui_tools/boxes.py

@@ -20,7 +20,8 @@
     STREAM_TOPIC_SEPARATOR, TIME_MENTION_MARKER,
 )
 from zulipterminal.helper import (
-    Message, format_string, match_emoji, match_group, match_stream, match_user,
+    Message, format_string, match_emoji, match_group, match_stream,
+    match_topics, match_user,
 )
 from zulipterminal.ui_tools.tables import render_table
 from zulipterminal.urwid_types import urwid_Size
@@ -95,6 +96,11 @@ def stream_box_view(self, stream_id: int, caption: str='', title: str='',
         )
         self.title_write_box = ReadlineEdit(caption="Topic:  ",
                                             edit_text=title)
+        self.title_write_box.enable_autocomplete(
+            func=self._topic_box_autocomplete,
+            key=keys_for_command('AUTOCOMPLETE').pop(),
+            key_reverse=keys_for_command('AUTOCOMPLETE_REVERSE').pop()
+        )
 
         header_write_box = urwid.Columns([
             urwid.LineBox(
@@ -114,6 +120,16 @@ def stream_box_view(self, stream_id: int, caption: str='', title: str='',
         ]
         self.contents = write_box
 
+    def _topic_box_autocomplete(self, text: str, state: Optional[int]
+                                ) -> Optional[str]:
+        topic_names = self.model.topics_in_stream(self.stream_id)
+
+        topic_typeaheads = match_topics(topic_names, text)
+
+        # Typeaheads and suggestions are the same.
+        return self._process_typeaheads(topic_typeaheads, state,
+                                        topic_typeaheads)
+
     def _stream_box_autocomplete(self, text: str, state: Optional[int]
                                  ) -> Optional[str]:
         streams_list = self.view.pinned_streams + self.view.unpinned_streams