model/views: Show edit history using EditHistoryView.

This GETs 'message_history', using message id, from the server and
displays it in the EditHistoryView. The EditHistoryView (popup) can be
triggered with 'EDIT_HISTORY' key from the MsgInfoView.

The following information is displayed in the view:
* topic (with 'updated from' prefix if it's been updated)
* timestamp
* author name
* tag (for current and original message)
* content

Author: preetmishra

zulipterminal/model.py

@@ -356,6 +356,16 @@ def get_messages(self, *,
             return ""
         return response['msg']
 
+    def get_message_history(self, message: Message) -> str:
+        """
+        GETs 'message_history' using messsage id.
+        """
+        response = self.client.get_message_history(message_id=message['id'])
+        if response['result'] == 'success':
+            message['message_history'] = response['message_history']
+            return ''
+        return response['msg']
+
     def get_topics_in_stream(self, stream_list: Iterable[int]) -> str:
         """
         Fetch all topics with specified stream_id's and

zulipterminal/ui_tools/views.py

@@ -1,7 +1,7 @@
 import threading
 import time
 from collections import OrderedDict
-from typing import Any, Callable, List, Optional, Tuple
+from typing import Any, Callable, Dict, List, Optional, Tuple
 
 import urwid
 
@@ -940,8 +940,61 @@ def __init__(self, controller: Any, msg: Any) -> None:
         self.controller = controller
         self.msg = msg
         self.width = 64
-        self.height = 0
-        super().__init__(controller, [], 'MSG_INFO')
+        self.height = 10
+
+        self.widgets = []
+        # NOTE: 'edit_history' is likely to be changed to a boolean value in
+        # the future.
+        if 'edit_history' in self.msg:
+            self.controller.model.get_message_history(self.msg)
+            for index, snapshot in enumerate(self.msg['message_history']):
+                if index == len(self.msg['message_history']) - 1:
+                    self.widgets.append(self.build_pile(snapshot, 'Current'))
+                    continue
+                elif index == 0:
+                    self.widgets.append(self.build_pile(snapshot, 'Original'))
+                else:
+                    self.widgets.append(self.build_pile(snapshot))
+                self.widgets.append(urwid.Text(''))  # Add newline.
+        else:
+            self.height = 1
+            text = 'The content has not been edited.'
+            self.widgets = [urwid.Text(text, align='center')]
+
+        super().__init__(controller, self.widgets, 'MSG_INFO')
+
+    def build_pile(self, snapshot: Dict[str, Any], tag: str='') -> Any:
+        timestamp = time.ctime(snapshot['timestamp'])[:-5]
+        full_name = self.get_full_name(snapshot['user_id'])
+        topic = snapshot['topic']
+        if 'prev_topic' in snapshot and topic != snapshot['prev_topic']:
+            topic += ' (updated from {})'.format(snapshot['prev_topic'])
+
+        header = urwid.Columns([
+                urwid.Text(('edit_topic', topic)),
+                (19, urwid.Text(('edit_time', timestamp))),
+            ], dividechars=2,
+        )
+        subheader = urwid.Columns([
+                urwid.Text(('edit_author', full_name)),
+                (18, urwid.Text(('edit_tag', '({} Version)'.format(tag) if tag
+                                else ''), align='right')),
+            ], dividechars=2,
+        )
+        message = urwid.Text(snapshot['content'])
+        return urwid.Pile([urwid.AttrWrap(header, 'popup_contrast'), subheader,
+                           message])
+
+    def get_full_name(self, user_id: int) -> str:
+        if self.msg['sender_id'] == user_id:
+            return self.msg['sender_full_name']
+        else:
+            for user in self.controller.view.users:
+                if user['user_id'] == user_id:
+                    return user['full_name']
+        # NOTE: This return statement is redundant and only put here to pass
+        # mypy as a user with `user_id` will always exist.
+        return ''
 
     def keypress(self, size: urwid_Size, key: str) -> str:
         if (is_command_key('GO_BACK', key)