boxes: Add footlinks in MessageBox.

The footlinks are shown below the message content with a style that is
different from the rest of the message content but similar to msg_links.

Test added.

Fixes zulip#618.

tests/ui/test_ui_tools.py

@@ -2147,6 +2147,26 @@ def test_reactions_view(self, message_fixture, to_vary_in_each_message):
             ('reaction_mine', 9),
         ]
 
+    @pytest.mark.parametrize(['message_links', 'expected_text',
+                              'expected_attrib'], [
+            ([('#T1', 'https://github.com/zulip/zulip-terminal/pull/1')],
+             '1: https://github.com/zulip/zulip-terminal/pull/1',
+             [('msg_footlink', 49)]),
+            ([('Foo!', 'https://foo.com'), ('Bar!', 'https://bar.com')],
+             '1: https://foo.com\n2: https://bar.com',
+             [('msg_footlink', 37)]),
+        ],
+        ids=['one_footlink', 'more_than_one_footlink']
+    )
+    def test_footlinks_view(self, message_fixture, message_links,
+                            expected_text, expected_attrib):
+        msg_box = MessageBox(message_fixture, self.model, None)
+
+        footlinks = msg_box.footlinks_view(message_links)
+
+        assert footlinks.original_widget.text == expected_text
+        assert footlinks.original_widget.attrib == expected_attrib
+
     @pytest.mark.parametrize(
         'key', keys_for_command('ENTER'),
         ids=lambda param: 'left_click-key:{}'.format(param)

zulipterminal/ui_tools/boxes.py

@@ -402,6 +402,23 @@ def reactions_view(self, reactions: List[Dict[str, Any]]) -> Any:
         except Exception:
             return ''
 
+    def footlinks_view(self, message_links: List[Tuple[str, str]]) -> Any:
+        if not message_links:
+            return ''
+
+        indexed_links = [
+            '{}: {}\n'.format(index, link)
+            for index, (text, link) in enumerate(message_links, start=1)
+        ]
+        indexed_links[-1] = indexed_links[-1][:-1]  # Remove the last newline.
+
+        footlinks = [
+            ('msg_footlink', indexed_link)
+            for indexed_link in indexed_links
+        ]
+        return urwid.Padding(urwid.Text(footlinks), align='left', left=10,
+                             width=('relative', 100), min_width=10, right=5)
+
     def soup2markup(self, soup: Any, **state: Any) -> List[Any]:
         # Ensure a string is provided, in case the soup finds none
         # This could occur if eg. an image is removed or not shown
@@ -658,11 +675,15 @@ def main_view(self) -> List[Any]:
         # Reactions
         reactions = self.reactions_view(self.message['reactions'])
 
+        # Footlinks.
+        footlinks = self.footlinks_view(self.message_links)
+
         # Build parts together and return
         parts = [
             (recipient_header, recipient_header is not None),
             (content_header, any_differences),
             (content, True),
+            (footlinks, footlinks != ''),
             (reactions, reactions != ''),
         ]
         return [part for part, condition in parts if condition]