Add custom Ansible filter plugin get_category_entries

This commit introduces a new Ansible filter plugin named
'get_category_entries', which returns all role names under the
roles/ directory that start with a given prefix.

Additionally, unit tests (unittest framework) have been added under
tests/unit/filterplugins/ to ensure correct behavior, including:

- Returns empty list when roles/ directory is missing
- Correctly filters and sorts by prefix
- Ignores non-directory entries
- Supports custom roles_path argument
- Returns all roles when prefix is empty

Reference: https://chatgpt.com/share/68a2f1ab-1fe8-800f-b22a-28c1c95802c2

filter_plugins/get_category_entries.py

@@ -0,0 +1,31 @@
+# Custom Ansible filter to get all role names under "roles/" with a given prefix.
+
+import os
+
+def get_category_entries(prefix, roles_path="roles"):
+    """
+    Returns a list of role names under the given roles_path
+    that start with the specified prefix.
+
+    :param prefix: String prefix to match role names.
+    :param roles_path: Path to the roles directory (default: 'roles').
+    :return: List of matching role names.
+    """
+    if not os.path.isdir(roles_path):
+        return []
+
+    roles = []
+    for entry in os.listdir(roles_path):
+        full_path = os.path.join(roles_path, entry)
+        if os.path.isdir(full_path) and entry.startswith(prefix):
+            roles.append(entry)
+
+    return sorted(roles)
+
+class FilterModule(object):
+    """ Custom filters for Ansible """
+
+    def filters(self):
+        return {
+            "get_category_entries": get_category_entries
+        }

tests/unit/filter_plugins/test_get_category_entries.py

@@ -0,0 +1,85 @@
+# Unit tests for the get_category_entries Ansible filter plugin (unittest version).
+
+import os
+import unittest
+import tempfile
+import shutil
+from pathlib import Path
+
+from filter_plugins.get_category_entries import get_category_entries
+
+
+class TestGetCategoryEntries(unittest.TestCase):
+    def setUp(self):
+        # Create an isolated temp directory for each test
+        self._tmpdir = tempfile.TemporaryDirectory()
+        self.tmp = Path(self._tmpdir.name)
+
+    def tearDown(self):
+        # Clean up the temp directory
+        self._tmpdir.cleanup()
+
+    def test_returns_empty_when_roles_dir_missing(self):
+        """If the roles directory does not exist, the filter must return an empty list."""
+        missing_dir = self.tmp / "no_such_roles_dir"
+        self.assertFalse(missing_dir.exists())
+        self.assertEqual(get_category_entries("docker-", roles_path=str(missing_dir)), [])
+
+    def test_matches_prefix_and_sorts(self):
+        """
+        The filter should return only directory names starting with the prefix,
+        and the result must be sorted.
+        """
+        roles_dir = self.tmp / "roles"
+        roles_dir.mkdir()
+
+        # Create role directories
+        (roles_dir / "docker-nginx").mkdir()
+        (roles_dir / "docker-postgres").mkdir()
+        (roles_dir / "web-app-keycloak").mkdir()
+        (roles_dir / "docker-redis").mkdir()
+
+        # A file that should be ignored
+        (roles_dir / "docker-file").write_text("not a directory")
+
+        result = get_category_entries("docker-", roles_path=str(roles_dir))
+        self.assertEqual(result, ["docker-nginx", "docker-postgres", "docker-redis"])
+
+    def test_ignores_non_directories(self):
+        """Non-directory entries under roles/ must be ignored."""
+        roles_dir = self.tmp / "roles"
+        roles_dir.mkdir()
+
+        (roles_dir / "docker-engine").mkdir()
+        (roles_dir / "docker-engine.txt").write_text("file, should be ignored")
+
+        result = get_category_entries("docker-", roles_path=str(roles_dir))
+        self.assertEqual(result, ["docker-engine"])
+
+    def test_respects_custom_roles_path(self):
+        """When roles_path is provided, the filter should use it instead of 'roles'."""
+        custom_roles = self.tmp / "custom" / "rolesdir"
+        custom_roles.mkdir(parents=True)
+
+        (custom_roles / "docker-a").mkdir()
+        (custom_roles / "docker-b").mkdir()
+        (custom_roles / "other-c").mkdir()
+
+        result = get_category_entries("docker-", roles_path=str(custom_roles))
+        self.assertEqual(result, ["docker-a", "docker-b"])
+
+    def test_empty_prefix_returns_all_roles_sorted(self):
+        """If an empty prefix is passed, the filter should return all role directories (sorted)."""
+        roles_dir = self.tmp / "roles"
+        roles_dir.mkdir()
+
+        (roles_dir / "a-role").mkdir()
+        (roles_dir / "c-role").mkdir()
+        (roles_dir / "b-role").mkdir()
+
+        result = get_category_entries("", roles_path=str(roles_dir))
+        self.assertEqual(result, ["a-role", "b-role", "c-role"])
+
+
+if __name__ == "__main__":
+    unittest.main()