fix: handle nonetype on existing suffix (#308)

* fix: handle nonetype existing suffix

* test: fix return value

* fix: improved regex

* docs: add fix changelog

Author: asajjad2

src/common/changelog.d/20250819_163705_areebsajjad21_fix_nonetype_handling.md

@@ -0,0 +1,43 @@
+<!--
+A new scriv changelog fragment.
+
+Uncomment the section that is right (remove the HTML comment wrapper).
+For top level release notes, leave all the headers commented out.
+-->
+
+<!--
+### Removed
+
+- A bullet item for the Removed category.
+
+-->
+<!--
+### Added
+
+- A bullet item for the Added category.
+
+-->
+<!--
+### Changed
+
+- A bullet item for the Changed category.
+
+-->
+<!--
+### Deprecated
+
+- A bullet item for the Deprecated category.
+
+-->
+
+### Fixed
+
+- Improved username collision detection regex to be more precise and avoid false matches
+- Added proper error handling for username suffix extraction in `_find_available_username`
+
+<!--
+### Security
+
+- A bullet item for the Security category.
+
+-->

src/common/mitol/common/utils/user.py

@@ -109,13 +109,22 @@ def _find_available_username(  # noqa: RET503
         ]
         # Find usernames that match the username base and have a numerical
         # suffix, then find the max suffix
-        filter_kwargs = {f"{username_field}__regex": rf"{username_base}[0-9]+"}
+        filter_kwargs = {f"{username_field}__regex": rf"^{username_base}\d+$"}
         existing_usernames = model.objects.filter(**filter_kwargs).values_list(
             username_field, flat=True
         )
-        max_suffix = max_or_none(
-            int(re.search(r"\d+$", username).group()) for username in existing_usernames
-        )
+
+        suffixes = []
+        for username in existing_usernames:
+            match = re.search(r"\d+$", username)
+            if match is not None:
+                try:
+                    suffixes.append(int(match.group()))
+                except (ValueError, AttributeError):
+                    continue
+
+        max_suffix = max_or_none(suffixes) if suffixes else None
+
         if max_suffix is None:
             return "".join([username_base, str(current_min_suffix)])
         else:

tests/common/utils/test_user.py

@@ -215,6 +215,16 @@ def test_create_user_initial_username_too_short(mock_find_username, fake_user):
             ["abcdefgh97", "abcdefgh98", "abcdefgh99"],
             "abcdefg100",
         ),
+        (
+            "someuser",
+            ["someuser2dy"],
+            "someuser1",
+        ),
+        (
+            "someuser",
+            ["someuser1", "someuser2dy", "someuser5"],
+            "someuser6",
+        ),
     ],
 )
 def test_find_available_username(username_base, existing_usernames, expected):