boxes/helper: Fixed generation of quote fences.

This commit incorporated some refactoring as well as fixing
correct quote fence generation.
Fences are generated after searching for maximum length occurence of `
and wrapping the quote block with the generated fence. This allows for
proper quoting of messages containing a code-block or another quote inside
them.
This is the first part of commit for this Pull-request.

zulipterminal/helper.py

@@ -5,7 +5,7 @@
 from collections import OrderedDict, defaultdict
 from functools import wraps
 from itertools import chain, combinations
-from re import ASCII, match
+from re import ASCII, MULTILINE, findall, match
 from threading import Thread
 from typing import (
     Any, Callable, DefaultDict, Dict, FrozenSet, Iterable, List, Set, Tuple,
@@ -657,6 +657,19 @@ def hash_util_decode(string: str) -> str:
     return unquote(string.replace('.', '%'))
 
 
+def get_unused_fence(content: Any) -> Any:
+    fence_length_regex = '^ {0,3}(`{3,})'
+    max_length_fence = 3
+
+    matches = findall(fence_length_regex, content,
+                      flags=MULTILINE)
+    if len(matches) != 0:
+        max_length_fence = max(max_length_fence,
+                               len(max(matches, key=len)) + 1)
+
+    return '`' * max_length_fence
+
+
 def all_user_ids_in_pm(message: Any) -> Any:
     """
     Returns a sorted list of all user_ids invloved in

zulipterminal/ui_tools/boxes.py

@@ -22,8 +22,8 @@
     STREAM_TOPIC_SEPARATOR, TIME_MENTION_MARKER,
 )
 from zulipterminal.helper import (
-    Message, absolute_url_of_message, format_string, match_emoji, match_group,
-    match_stream, match_topics, match_user,
+    Message, absolute_url_of_message, format_string, get_unused_fence,
+    match_emoji, match_group, match_stream, match_topics, match_user,
 )
 from zulipterminal.ui_tools.buttons import EditModeButton
 from zulipterminal.ui_tools.tables import render_table
@@ -1192,16 +1192,15 @@ def keypress(self, size: urwid_Size, key: str) -> Optional[str]:
             #   ```quote
             #   message_content
             #   ```
-            quote = '@_**{}|{}** '.format(self.message['sender_full_name'],
-                                          self.message['sender_id'])
-
-            # FIXME: The type and generation of link needs to be discussed.
-            # For interoperability webapp link should be given, but
-            # that would not narrow to the quoted message inside ZT.
             absolute_url = absolute_url_of_message(self.model, self.message)
-            quote += '[said]({}):\n'.format(absolute_url)
-            quote += '```quote\n' + self.model.client.get_raw_message(
-                self.message['id'])['raw_content'] + '\n```\n'
+            quote = '@_**{}|{}** [said]({}):\n'.format(
+                        self.message['sender_full_name'],
+                        self.message['sender_id'], absolute_url)
+
+            fence = get_unused_fence(self.model.client.get_raw_message(
+                self.message['id'])['raw_content'])
+            quote += f'{fence}quote\n' + self.model.client.get_raw_message(
+                self.message['id'])['raw_content'] + f'\n{fence}\n'
             self.model.controller.view.write_box.msg_write_box.set_edit_text(
                 quote)
             self.model.controller.view.write_box.msg_write_box.set_edit_pos(