feat: Add MiddlewareDaemon implementation to revpi-middleware

Introduce the main daemon class for revpi-middleware with methods for
initialization, configuration, DBus handling, and a mainloop. This
implementation includes support for configuration reloads, log rotation,
and proper thread management for DBus operations.

src/revpi_middleware/daemon.py

@@ -0,0 +1,121 @@
+# -*- coding: utf-8 -*-
+# SPDX-FileCopyrightText: 2025 KUNBUS GmbH
+# SPDX-License-Identifier: GPL-2.0-or-later
+"""Main daemon of revpi-middleware."""
+
+from logging import getLogger
+from threading import Event
+from time import perf_counter
+
+from . import proginit as pi
+from .dbus_middleware1.bus_provider import BusProvider
+
+log = getLogger(__name__)
+
+
+class MiddlewareDaemon:
+    """Main program of MiddlewareDaemon class."""
+
+    def __init__(self):
+        """Init MiddlewareDaemon class."""
+        log.debug("enter MiddlewareDaemon.__init__")
+
+        self._cycle_time = 1.0
+        self.do_cycle = Event()
+        self._reconfigure = False
+        self._running = True
+
+        self.bus_provider = None
+
+        self._configure()
+        log.debug("leave MiddlewareDaemon.__init__")
+
+    def _configure(self) -> None:
+        """Load the configuration file and set values."""
+        log.debug("enter MiddlewareDaemon._configure")
+        pi.reload_conf()
+
+        log.debug("leave MiddlewareDaemon._configure")
+
+    def dbus_start(self):
+        log.debug("enter MiddlewareDaemon.dbus_start")
+        if self.bus_provider and self.bus_provider.is_alive():
+            return
+
+        self.bus_provider = BusProvider()
+        self.bus_provider.start()
+
+        log.debug("leave MiddlewareDaemon.dbus_start")
+
+    def dbus_stop(self):
+        log.debug("enter MiddlewareDaemon.dbus_stop")
+
+        if self.bus_provider:
+            self.bus_provider.stop()
+            self.bus_provider.join(timeout=10.0)
+            if self.bus_provider.is_alive():
+                log.warning("dbus provider thread is still alive")
+
+        log.debug("leave MiddlewareDaemon.dbus_stop")
+
+    def reload_config(self) -> None:
+        """Reload configuration file."""
+        log.debug("enter MiddlewareDaemon.reload_config")
+
+        self._reconfigure = True
+        self.do_cycle.set()
+
+        log.debug("leave MiddlewareDaemon.reload_config")
+
+    @staticmethod
+    def rotate_logfile() -> None:
+        """Start a new logfile."""
+        log.debug("enter MiddlewareDaemon.rotate_logfile")
+
+        pi.reconfigure_logger()
+        log.warning("start new logfile")
+
+        log.debug("leave MiddlewareDaemon.rotate_logfile")
+
+    def start(self) -> int:
+        """Blocking mainloop of program."""
+        log.debug("enter MiddlewareDaemon.start")
+        error_code = 0
+
+        # Startup tasks
+        self.dbus_start()
+
+        pi.startup_complete()
+        # Go into mainloop of daemon
+        while self._running:
+            ot = perf_counter()
+            self.do_cycle.clear()
+
+            # Early tasks of the cycle loop
+            if self._reconfigure:
+                self._configure()
+                self._reconfigure = False
+                pi.startup_complete()
+
+            # Cycle time calculation
+            dm = divmod(ot - perf_counter(), self._cycle_time)
+            # For float the result is (q, a % b), where q is usually math.floor(a / b) but may be 1 less than that.
+            if dm[0] == -1.0:  # Cycle time isn't exceeded
+                self.do_cycle.wait(dm[1])
+            else:
+                log.debug("Cycle time exceeded about {0:.0f} times".format(abs(dm[0])))
+
+        # Cleanup tasks
+        self.dbus_stop()
+
+        log.debug("leave MiddlewareDaemon.start")
+        return error_code
+
+    def stop(self) -> None:
+        """Set stop request for mainloop."""
+        log.debug("enter MiddlewareDaemon.stop")
+
+        self._running = False
+        self.do_cycle.set()
+
+        log.debug("leave MiddlewareDaemon.stop")