refactor: buttons: Validate PM data prior to narrowing.

This commit adds validation helper for PM data, in an attempt to
avoid and handle any potential exceptions before starting to switch
to the PM narrow. The validation checks if all the recipients are
valid private recpients or not, and whether the PM type is valid.

Tests added.

Author: Ezio-Sarthak

tests/ui_tools/test_buttons.py

@@ -984,6 +984,96 @@ def test__patch_stream_data(
 
         assert parsed_link == expected_parsed_link
 
+    @pytest.mark.parametrize(
+        [
+            "parsed_link",
+            "is_valid_private_recipient",
+            "expected_error",
+        ],
+        [
+            case(
+                ParsedNarrowLink(
+                    pm_with=DecodedPM(
+                        type=Literal["pm"],
+                        recipient_ids=[1001, 11],
+                        recipient_emails=["[email protected]", "[email protected]"],
+                    ),
+                ),  # ...
+                True,
+                "",
+                id="valid_pm_data",
+            ),
+            case(
+                ParsedNarrowLink(
+                    pm_with=DecodedPM(
+                        type=Literal["pm"],
+                        recipient_ids=[1001, 11, 12],
+                        recipient_emails=[
+                            "[email protected]",
+                            "[email protected]",
+                            "[email protected]",
+                        ],
+                    ),
+                ),  # ...
+                True,
+                "Invalid PM type",
+                id="invalid_pm_data",
+            ),
+            case(
+                ParsedNarrowLink(
+                    pm_with=DecodedPM(
+                        type=Literal["group"],
+                        recipient_ids=[1001, 11, 12],
+                        recipient_emails=[
+                            "[email protected]",
+                            "[email protected]",
+                            "[email protected]",
+                        ],
+                    ),
+                ),  # ...
+                True,
+                "",
+                id="valid_group_pm_data",
+            ),
+            case(
+                ParsedNarrowLink(
+                    pm_with=DecodedPM(
+                        type=Literal["group"],
+                        recipient_ids=[1001, 11],
+                        recipient_emails=["[email protected]", "[email protected]"],
+                    ),
+                ),  # ...
+                True,
+                "Invalid PM type",
+                id="invalid_group_pm_data",
+            ),
+            case(
+                ParsedNarrowLink(
+                    pm_with=DecodedPM(
+                        type=Literal["pm"],
+                        recipient_ids=[1001, -1],
+                        recipient_emails=["[email protected]", ""],
+                    ),
+                ),  # ...
+                False,
+                "The PM has one or more invalid recipient(s)",
+                id="invalid_recipient",
+            ),
+        ],
+    )
+    def test__validate_pm_data(
+        self,
+        parsed_link: ParsedNarrowLink,
+        is_valid_private_recipient: bool,
+        expected_error: str,
+    ) -> None:
+        self.controller.model.is_valid_private_recipient.return_value = (
+            is_valid_private_recipient
+        )
+        mocked_button = self.message_link_button()
+
+        assert mocked_button._validate_pm_data(parsed_link) == expected_error
+
     @pytest.mark.parametrize(
         [
             "parsed_link",

zulipterminal/ui_tools/buttons.py

@@ -543,6 +543,31 @@ def _validate_stream_data(self, parsed_link: ParsedNarrowLink) -> str:
 
         return ""
 
+    def _validate_pm_data(self, parsed_link: ParsedNarrowLink) -> str:
+        """
+        Validates PM data and returns either an empty string for a successful
+        validation or an appropriate validation error.
+        """
+        pm_type = parsed_link["pm_with"]["type"]
+        recipient_ids = parsed_link["pm_with"]["recipient_ids"]
+        recipient_emails = parsed_link["pm_with"]["recipient_emails"]
+
+        # If a group PM is specified as normal PM or vice versa.
+        if (len(recipient_ids) >= 3 and pm_type == Literal["pm"]) or (
+            len(recipient_ids) <= 2 and pm_type == Literal["group"]
+        ):
+            return "Invalid PM type"
+
+        # Validate all PM recipients
+        for i in range(len(recipient_ids)):
+            id = recipient_ids[i]
+            email = recipient_emails[i]
+
+            if not self.model.is_valid_private_recipient(id, email):
+                return "The PM has one or more invalid recipient(s)"
+
+        return ""
+
     def _validate_narrow_link(self, parsed_link: ParsedNarrowLink) -> str:
         """
         Returns either an empty string for a successful validation or an
@@ -559,6 +584,12 @@ def _validate_narrow_link(self, parsed_link: ParsedNarrowLink) -> str:
             # On successful validation, patch the optional stream data
             self._patch_stream_data(parsed_link)
 
+        # Validate PM data.
+        if "pm-with" in parsed_link:
+            error = self._validate_pm_data(parsed_link)
+            if error:
+                return error
+
         # Validate topic name.
         if "topic_name" in parsed_link:
             topic_name = parsed_link["topic_name"]