refactor(dbus): Move simple_systemd to systemd_helper

Moved the `simple_systemd` function to a dedicated `systemd_helper`
module to improve code organization and reusability. Updated imports
accordingly in affected files.

Signed-off-by: Sven Sager <s.sager@kunbus.com>

src/revpi_middleware/dbus_middleware1/systemd_helper.py

@@ -0,0 +1,118 @@
+# -*- coding: utf-8 -*-
+# SPDX-FileCopyrightText: 2025 KUNBUS GmbH
+# SPDX-License-Identifier: GPL-2.0-or-later
+from enum import Enum
+from logging import getLogger
+from threading import Thread
+from typing import Optional
+
+from pydbus import SystemBus
+
+log = getLogger(__name__)
+
+
+class ServiceActions(Enum):
+    """
+    Enumeration class for defining configuration actions.
+
+    This enumeration provides predefined constants for common configuration
+    actions. It can be used to ensure consistency when working with or defining
+    such actions in a system.
+    """
+
+    ENABLE = "enable"
+    DISABLE = "disable"
+    STATUS = "status"
+    AVAILABLE = "available"
+
+
+def simple_systemd(action: ServiceActions, unit: str, unmask: bool = False) -> Optional[bool]:
+    """
+    Perform systemd service actions such as enable, disable, check status, or availability.
+
+    This function interacts with the systemd D-Bus API to manage and query the
+    state of services on a system. The supported actions include enabling a systemd
+    unit, disabling it, starting/stopping a unit, and checking its status or
+    availability. The function supports asynchronous configuration changes through
+    threads where applicable.
+
+    Parameters:
+        action (ServiceActions): The action to perform on the systemd service.
+            Supported actions are ENABLE, DISABLE, STATUS, and AVAILABLE.
+        unit (str): The name of the systemd unit to operate on (e.g., "example.service").
+        unmask (bool): When enabling a unit, if True, any masked unit file will
+            first be unmasked before proceeding with the operation. Defaults to False.
+
+    Returns:
+        Optional[bool]: The return value depends on the action. For STATUS or
+            AVAILABLE actions, it returns True if the unit satisfies the condition
+            (e.g., enabled and active, or available and loaded), False otherwise.
+            For other actions, it returns None.
+    """
+    bus = SystemBus()
+    systemd = bus.get(
+        "org.freedesktop.systemd1",
+        "/org/freedesktop/systemd1",
+    )
+    systemd_manager = systemd["org.freedesktop.systemd1.Manager"]
+
+    if action is ServiceActions.ENABLE:
+
+        def thread_unit_config():
+            """Change configuration asynchronously."""
+            lst_change_unmask = []
+            if unmask:
+                # Dbus call: UnmaskUnitFiles(in as files, in b runtime, out a(sss) changes
+                lst_change_unmask = systemd_manager.UnmaskUnitFiles([unit], False)
+
+            # Dbus call: EnableUnitFiles(in as files, in b runtime, in b force,
+            #                            out b carries_install_info, out a(sss) changes
+            lst_change_enable = systemd_manager.EnableUnitFiles([unit], False, False)
+            if lst_change_unmask or lst_change_enable:
+                # Reload systemd after modified unit property
+                systemd_manager.Reload()
+
+        Thread(target=thread_unit_config, daemon=True).start()
+
+        # Dbus call: StartUnit(in s name, in s mode, out o job
+        systemd_manager.StartUnit(unit, "replace")
+
+    elif action is ServiceActions.DISABLE:
+
+        def thread_unit_config():
+            """Change configuration asynchronously."""
+            # Dbus call: DisableUnitFiles (in as files, in b runtime, out a(sss) changes)
+            change = systemd_manager.DisableUnitFiles([unit], False)
+            if change:
+                # Reload systemd after modified unit property
+                systemd_manager.Reload()
+
+        Thread(target=thread_unit_config, daemon=True).start()
+
+        # Dbus call: StopUnit(in s name,in s mode, out o job
+        systemd_manager.StopUnit(unit, "replace")
+
+    elif action is ServiceActions.STATUS:
+        try:
+            unit_path = systemd_manager.LoadUnit(unit)
+            properties = bus.get("org.freedesktop.systemd1", unit_path)
+        except Exception:
+            log.warning(f"could not get systemd unit {unit}")
+            return False
+
+        return properties.UnitFileState == "enabled" and properties.ActiveState == "active"
+
+    elif action is ServiceActions.AVAILABLE:
+        try:
+            unit_path = systemd_manager.LoadUnit(unit)
+            properties = bus.get("org.freedesktop.systemd1", unit_path)
+        except Exception:
+            log.warning(f"could not get systemd unit {unit}")
+            return False
+
+        return properties.LoadState != "not-found"
+
+    else:
+        raise ValueError(f"action {action} not supported")
+
+    return None