refactor: implement generic optional import mechanisms

this project is actively using optional imports, which leads to
duplicate handling here and there. This commit implements logic in
special method to reduce complexity and simplify tests paths

ahriman-core/src/ahriman/core/log/journal_handler.py

@@ -21,6 +21,8 @@
 from logging import NullHandler
 from typing import Any
 
+from ahriman.core.module_loader import optional_module
+
 
 __all__ = ["JournalHandler"]
 
@@ -40,7 +42,5 @@ class _JournalHandler(NullHandler):
         del args, kwargs
 
 
-try:
-    from systemd.journal import JournalHandler  # type: ignore[import-untyped]
-except ImportError:
-    JournalHandler = _JournalHandler
+systemd_journal = optional_module("systemd.journal")
+JournalHandler = systemd_journal.JournalHandler if systemd_journal else _JournalHandler

ahriman-core/src/ahriman/core/log/log_loader.py

@@ -26,6 +26,7 @@ from typing import ClassVar, Literal
 from ahriman.core.configuration import Configuration
 from ahriman.core.log.http_log_handler import HttpLogHandler
 from ahriman.core.log.log_context import LogContext
+from ahriman.core.module_loader import optional_module
 from ahriman.models.log_handler import LogHandler
 from ahriman.models.repository_id import RepositoryId
 
@@ -65,14 +66,11 @@ class LogLoader:
         if selected is not None:
             return selected
 
-        try:
-            from systemd.journal import JournalHandler  # type: ignore[import-untyped]
-            del JournalHandler
+        if optional_module("systemd.journal"):
             return LogHandler.Journald  # journald import was found
-        except ImportError:
-            if LogLoader.DEFAULT_SYSLOG_DEVICE.exists():
-                return LogHandler.Syslog
-            return LogHandler.Console
+        if LogLoader.DEFAULT_SYSLOG_DEVICE.exists():
+            return LogHandler.Syslog
+        return LogHandler.Console
 
     @staticmethod
     def load(repository_id: RepositoryId, configuration: Configuration, handler: LogHandler, *,

ahriman-core/src/ahriman/core/module_loader.py

@@ -26,8 +26,7 @@ from pkgutil import ModuleInfo, walk_packages
 from types import ModuleType
 from typing import Any, TypeGuard, TypeVar
 
-
-__all__ = ["implementations"]
+__all__ = ["implementations", "optional_module"]
 
 
 T = TypeVar("T")
@@ -74,3 +73,19 @@ def implementations(root_module: ModuleType, base_class: type[T]) -> Iterator[ty
 
             for _, attribute in inspect.getmembers(module, is_base_class):
                 yield attribute
+
+
+def optional_module(module_name: str) -> ModuleType | None:
+    """
+    import an optional module
+
+    Args:
+        module_name(str): fully qualified module name
+
+    Returns:
+        ModuleType | None: imported module or ``None`` when it cannot be imported
+    """
+    try:
+        return import_module(module_name)
+    except ImportError:
+        return None

ahriman-core/tests/ahriman/core/test_module_loader.py

@@ -2,7 +2,7 @@ import ahriman.web.views
 
 from pathlib import Path
 
-from ahriman.core.module_loader import _modules, implementations
+from ahriman.core.module_loader import _modules, implementations, optional_module
 from ahriman.web.views.base import BaseView
 
 
@@ -23,3 +23,17 @@ def test_implementations() -> None:
     assert routes
     assert all(isinstance(view, type) for view in routes)
     assert all(issubclass(view, BaseView) for view in routes)
+
+
+def test_optional_module() -> None:
+    """
+    must import an available module
+    """
+    assert optional_module("ahriman.web.views") is ahriman.web.views
+
+
+def test_optional_module_fallback() -> None:
+    """
+    must return none when the module cannot be imported
+    """
+    assert optional_module("missing_ahriman_module") is None