model: Store _have_last_message for each narrow.

Currently, _have_last_message is not stored per-narrow. This leads to
message loading bugs when switching between narrows, where the previous
narrow was not fully loaded.

Tests amended.

To reproduce this (now fixed) bug,
* Go to stream A which has been fully loaded. (By pressing `down`)
  _have_last_message is set to True
* Go to stream B and press `down` but B is still not fully loaded.
  Hence, _have_last_message is set to False
* Recieving message on stream A now won't add it to the Stream A view.

Author: kaustubh-nair

tests/model/test_model.py

@@ -44,7 +44,7 @@ def test_init(self, model, initial_data, user_profile):
         assert model.msg_view is None
         assert model.msg_list is None
         assert model.narrow == []
-        assert model._have_last_message is False
+        assert isinstance(model._have_last_message, dict)
         assert model.stream_id == -1
         assert model.stream_dict == {}
         assert model.recipients == frozenset()
@@ -467,7 +467,7 @@ def test_success_get_messages(self, mocker, messages_successful_response,
         anchor = messages_successful_response['anchor']
         if anchor < 10000000000000000:
             assert model.index['pointer'][repr(model.narrow)] == anchor
-        assert model._have_last_message is True
+        assert model._have_last_message[repr(model.narrow)] is True
 
     def test_get_message_false_first_anchor(
             self, mocker, messages_successful_response, index_all_messages,
@@ -503,9 +503,9 @@ def test_get_message_false_first_anchor(
 
         # TEST `query_range` < no of messages received
         # RESET model._have_last_message value
-        model._have_last_message = False
+        model._have_last_message[repr(model.narrow)] = False
         model.get_messages(num_after=0, num_before=0, anchor=0)
-        assert model._have_last_message is False
+        assert model._have_last_message[repr(model.narrow)] is False
 
     # FIXME This only tests the case where the get_messages is in __init__
     def test_fail_get_messages(self, mocker, error_response,
@@ -653,7 +653,7 @@ def test__stream_info_from_subscriptions(self, initial_data, streams,
 
     def test__handle_message_event_with_Falsey_log(self, mocker,
                                                    model, message_fixture):
-        model._have_last_message = True
+        model._have_last_message[repr([])] = True
         mocker.patch('zulipterminal.model.Model._update_topic_index')
         index_msg = mocker.patch('zulipterminal.model.index_messages',
                                  return_value={})
@@ -674,7 +674,7 @@ def test__handle_message_event_with_Falsey_log(self, mocker,
 
     def test__handle_message_event_with_valid_log(self, mocker,
                                                   model, message_fixture):
-        model._have_last_message = True
+        model._have_last_message[repr([])] = True
         mocker.patch('zulipterminal.model.Model._update_topic_index')
         index_msg = mocker.patch('zulipterminal.model.index_messages',
                                  return_value={})
@@ -697,7 +697,7 @@ def test__handle_message_event_with_valid_log(self, mocker,
 
     def test__handle_message_event_with_flags(self, mocker,
                                               model, message_fixture):
-        model._have_last_message = True
+        model._have_last_message[repr([])] = True
         mocker.patch('zulipterminal.model.Model._update_topic_index')
         index_msg = mocker.patch('zulipterminal.model.index_messages',
                                  return_value={})
@@ -762,7 +762,7 @@ def test__handle_message_event_with_flags(self, mocker,
             'mentioned_msg_in_mentioned_msg_narrow'])
     def test__handle_message_event(self, mocker, user_profile, response,
                                    narrow, recipients, model, log):
-        model._have_last_message = True
+        model._have_last_message[repr(narrow)] = True
         mocker.patch('zulipterminal.model.Model._update_topic_index')
         index_msg = mocker.patch('zulipterminal.model.index_messages',
                                  return_value={})
@@ -783,7 +783,7 @@ def test__handle_message_event(self, mocker, user_profile, response,
         assert model.msg_list.log == log
         set_count.assert_called_once_with([response['id']], self.controller, 1)
 
-        model._have_last_message = False
+        model._have_last_message[repr(narrow)] = False
         model.notify_user.assert_called_once_with(response)
         model._handle_message_event(event)
         # LOG REMAINS THE SAME IF UPDATE IS FALSE

zulipterminal/model.py

@@ -69,7 +69,7 @@ def __init__(self, controller: Any) -> None:
         self.msg_view = None  # type: Any
         self.msg_list = None  # type: Any
         self.narrow = []  # type: List[Any]
-        self._have_last_message = False
+        self._have_last_message = {}  # type: Dict[str, bool]
         self.stream_id = -1
         self.recipients = frozenset()  # type: FrozenSet[Any]
         self.index = initial_index
@@ -349,16 +349,18 @@ def get_messages(self, *,
         response = self.client.get_messages(message_filters=request)
         if response['result'] == 'success':
             self.index = index_messages(response['messages'], self, self.index)
+            narrow_str = repr(self.narrow)
             if first_anchor and response['anchor'] != 10000000000000000:
-                self.index['pointer'][repr(self.narrow)] = response['anchor']
+                self.index['pointer'][narrow_str] = response['anchor']
             if 'found_newest' in response:
-                self._have_last_message = response['found_newest']
+                self._have_last_message[narrow_str] = response['found_newest']
             else:
                 # Older versions of the server does not contain the
                 # 'found_newest' flag. Instead, we use this logic:
                 query_range = num_after + num_before + 1
-                self._have_last_message = (len(response['messages'])
-                                           < query_range)
+                num_messages = len(response['messages'])
+                self._have_last_message[narrow_str] = (num_messages
+                                                       < query_range)
             return ""
         return response['msg']
 
@@ -742,7 +744,8 @@ def _handle_message_event(self, event: Event) -> None:
         if 'read' not in message['flags']:
             set_count([message['id']], self.controller, 1)
 
-        if hasattr(self.controller, 'view') and self._have_last_message:
+        if (hasattr(self.controller, 'view')
+                and self._have_last_message[repr(self.narrow)]):
             if self.msg_list.log:
                 last_message = self.msg_list.log[-1].original_widget.message
             else: