model: Add un_resolve_topic 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 (
@@ -1198,6 +1199,77 @@ def test_can_user_edit_topic(
         else:
             report_error.assert_called_once_with(expected_response[user_type][0])
 
+    @pytest.mark.parametrize(
+        "topic_name, msg_response, server_feature_level, return_value, expect_footer_error",
+        [
+            (
+                "hi!",
+                {
+                    "subject": "hi!",
+                    "timestamp": 11662271397,
+                    "id": 1,
+                },
+                12,
+                RESOLVED_TOPIC_PREFIX + "hi!",
+                False,
+            ),
+            (
+                "hi!",
+                {
+                    "subject": "hi!",
+                    "timestamp": 0,
+                    "id": 1,
+                },
+                None,
+                " Time limit for editing topic has been exceeded.",
+                True,
+            ),
+            (
+                "✔ hi!",
+                {
+                    "subject": "✔ hi!",
+                    "timestamp": 11662271397,
+                    "id": 1,
+                },
+                10,
+                "hi!",
+                False,
+            ),
+        ],
+    )
+    def test_un_resolve_topic(
+        self,
+        mocker,
+        model,
+        initial_data,
+        topic_name,
+        msg_response,
+        server_feature_level,
+        return_value,
+        expect_footer_error,
+        stream_id=1,
+    ):
+        model.initial_data = initial_data
+        model.server_feature_level = server_feature_level
+        initial_data["realm_community_topic_editing_limit_seconds"] = 86400
+        # If user can't edit topic, topic (un)resolve is disabled. Therefore,
+        # default return_value=True
+        model.can_user_edit_topic = mocker.Mock(return_value=True)
+        model.get_latest_message_in_topic = mocker.Mock(return_value=msg_response)
+        model.update_stream_message = mocker.Mock(return_value={"result": "success"})
+        report_error = model.controller.report_error
+
+        model.un_resolve_topic(stream_id, topic_name)
+
+        if not expect_footer_error:
+            model.update_stream_message.assert_called_once_with(
+                message_id=msg_response["id"],
+                topic=return_value,
+                propagate_mode="change_all",
+            )
+        else:
+            report_error.assert_called_once_with(return_value)
+
     # NOTE: This tests only getting next-unread, not a fixed anchor
     def test_success_get_messages(
         self,

zulipterminal/model.py

@@ -30,6 +30,7 @@
 
 from zulipterminal import unicode_emojis
 from zulipterminal.api_types import (
+    RESOLVED_TOPIC_PREFIX,
     Composition,
     EditPropagateMode,
     Event,
@@ -695,6 +696,35 @@ def can_user_edit_topic(self) -> bool:
         self.controller.report_error("User not found")
         return False
 
+    def un_resolve_topic(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) or None
+                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 = 86400
+                # 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 generate_all_emoji_data(
         self, custom_emoji: Dict[str, RealmEmojiData]
     ) -> Tuple[NamedEmojiData, List[str]]: