model: Add toggle_topic_resolved_status function to (un)resolve topics.

Fixes zulip#1075
The function calls get_latest_message_in_topic to fetch recent message
in topic to be (un)resolved. It verifies user and editing conditions
using can_user_edit_topic function and finally add or remove
RESOLVED_TOPIC_PREFIX from topic name.

tests/model/test_model.py

@@ -7,6 +7,7 @@
 from pytest import param as case
 from zulip import Client, ZulipError
 
+from zulipterminal.api_types import RESOLVED_TOPIC_PREFIX
 from zulipterminal.config.symbols import STREAM_TOPIC_SEPARATOR
 from zulipterminal.helper import initial_index, powerset
 from zulipterminal.model import (
@@ -1009,6 +1010,48 @@ def test_can_user_edit_topic(
         else:
             report_error.assert_called_once_with(expected_response[case])
 
+    @pytest.mark.parametrize(
+        "update_response, user_response, msg_response, return_value",
+        [
+            (
+                {"result": "success"},
+                True,
+                {
+                    "subject": "hi!",
+                    "stream_id": 1,
+                    "timestamp": 11662271397,
+                    "id": 1,
+                },
+                RESOLVED_TOPIC_PREFIX + "hi!",
+            ),
+        ],
+    )
+    def test_toggle_topic_resolved_status(
+        self,
+        mocker,
+        model,
+        initial_data,
+        update_response,
+        user_response,
+        msg_response,
+        return_value,
+    ):
+        model.initial_data = initial_data
+        initial_data["realm_community_topic_editing_limit_seconds"] = 259200
+        model.can_user_edit_topic = mocker.Mock(return_value=user_response)
+        model.get_latest_message_in_topic = mocker.Mock(return_value=msg_response)
+        model.update_stream_message = mocker.Mock(return_value=update_response)
+        report_error = model.controller.report_error
+
+        model.toggle_topic_resolved_status(
+            msg_response["stream_id"], msg_response["subject"]
+        )
+        model.update_stream_message.assert_called_once_with(
+            message_id=msg_response["id"],
+            topic=return_value,
+            propagate_mode="change_all",
+        )
+
     @pytest.mark.parametrize(
         "response, return_value",
         [

zulipterminal/model.py

@@ -30,6 +30,7 @@
 
 from zulipterminal import unicode_emojis
 from zulipterminal.api_types import (
+    RESOLVED_TOPIC_PREFIX,
     Composition,
     EditPropagateMode,
     Event,
@@ -638,6 +639,35 @@ def can_user_edit_topic(self) -> bool:
         self.controller.report_error("User not found")
         return False
 
+    def toggle_topic_resolved_status(self, stream_id: int, topic_name: str) -> None:
+        if self.can_user_edit_topic():
+            response = self.get_latest_message_in_topic(stream_id, topic_name)
+            if response:
+                time_since_msg_sent = time.time() - response["timestamp"]
+                # ZFL < 11, community_topic_editing_limit_seconds
+                # was hardcoded as int value in secs eg. 86400s (1 day)
+                if self.server_feature_level is None or self.server_feature_level >= 11:
+                    edit_time_limit = self.initial_data[
+                        "realm_community_topic_editing_limit_seconds"
+                    ]
+                else:
+                    edit_time_limit = 259200
+                # Don't allow editing topic if time-limit exceeded.
+                if time_since_msg_sent >= edit_time_limit:
+                    self.controller.report_error(
+                        " Time limit for editing topic has been exceeded."
+                    )
+                else:
+                    if topic_name.startswith(RESOLVED_TOPIC_PREFIX):
+                        topic_name = topic_name[2:]
+                    else:
+                        topic_name = RESOLVED_TOPIC_PREFIX + topic_name
+                    self.update_stream_message(
+                        message_id=response["id"],
+                        topic=topic_name,
+                        propagate_mode="change_all",
+                    )
+
     def update_stream_message(
         self,
         topic: str,