feat(dbus): Add ConfigTxt class for managing config.txt file

Introduced the ConfigTxt class to handle parsing, editing, and saving of
config.txt files. This includes methods for adding, clearing, and
retrieving configuration values, as well as handling dtoverlays and
dtparams. Enhanced system configuration capabilities by providing
structured support for config file operations.

src/revpi_middleware/dbus_middleware1/system_config/revpi_config.py

@@ -1,10 +1,15 @@
 # -*- coding: utf-8 -*-
 # SPDX-FileCopyrightText: 2025 KUNBUS GmbH
 # SPDX-License-Identifier: GPL-2.0-or-later
+import re
+import shutil
 import subprocess
+from collections import namedtuple
 from enum import Enum, IntEnum
 from logging import getLogger
 from os import X_OK, access
+from os.path import exists
+from typing import List
 
 from pydbus import SystemBus
 
@@ -12,6 +17,10 @@ from ..dbus_helper import grep
 
 log = getLogger(__name__)
 
+ConfigVariable = namedtuple("ConfigVariable", ["name", "value", "line_index"])
+
+CONFIG_TXT_LOCATIONS = ("/boot/firmware/config.txt", "/boot/config.txt")
+
 
 class ComputeModuleTypes(IntEnum):
     UNKNOWN = 0
@@ -69,7 +78,7 @@ class RevPiConfig:
             except ValueError:
                 pass
 
-        # Detect WiFi
+        # Detect WiFi on CM module
         could_have_wifi = self._cm_type in (ComputeModuleTypes.CM4, ComputeModuleTypes.CM5)
         if could_have_wifi:
             lst_grep = grep("DRIVER=brcmfmac", "/sys/class/ieee80211/phy0/device/uevent")
@@ -94,6 +103,89 @@ class RevPiConfig:
         return self._cm_with_wifi
 
 
+class ConfigTxt:
+    re_name_value = re.compile(r"^\s*(?!#)(?P<name>[^=\s].+?)\s*=\s*(?P<value>\S+)\s*$")
+
+    def __init__(self):
+        self._config_txt_path = ""
+        for path in CONFIG_TXT_LOCATIONS:
+            if exists(path):
+                self._config_txt_path = path
+                break
+
+        if not self._config_txt_path:
+            raise FileNotFoundError("no config.txt found")
+
+        self._config_txt_lines = []
+
+    def _clear_name_values(self, name: str, values: str or list) -> int:
+        counter = 0
+        if type(values) is str:
+            values = [values]
+
+        for config_var in self._get_all_name_values():
+            if config_var.name == name and config_var.value in values:
+                self._config_txt_lines.pop(config_var.line_index)
+                counter += 1
+
+        return counter
+
+    def _get_all_name_values(self) -> List[ConfigVariable]:
+        if not self._config_txt_lines:
+            self.reload_config()
+
+        lst_return = []
+
+        for i in range(len(self._config_txt_lines)):
+            match = self.re_name_value.match(self._config_txt_lines[i])
+            if match:
+                lst_return.append(ConfigVariable(match.group("name"), match.group("value"), i))
+
+        return lst_return
+
+    def reload_config(self):
+        with open(self._config_txt_path, "r") as f:
+            self._config_txt_lines = f.readlines()
+
+    def save_config(self):
+        if not self._config_txt_lines:
+            return
+
+        tmp_path = f"{self._config_txt_path}.tmp"
+        with open(tmp_path, "w") as f:
+            f.writelines(self._config_txt_lines)
+        shutil.move(tmp_path, self._config_txt_path)
+
+        self._config_txt_lines.clear()
+
+    def add_name_value(self, name: str, value: str):
+        # Check weather name and value already exists
+        for config_var in self._get_all_name_values():
+            if config_var.name == name and config_var.value == value:
+                return
+
+        self._config_txt_lines.append(f"{name}={value}\n")
+
+    def clear_dtoverlays(self, dtoverlays: str or list) -> int:
+        return self._clear_name_values("dtoverlay", dtoverlays)
+
+    def clear_dtparams(self, dtparams: str or list) -> int:
+        return self._clear_name_values("dtparam", dtparams)
+
+    def get_values(self, var_name: str) -> list:
+        var_values = []
+
+        for config_var in self._get_all_name_values():
+            if config_var.name == var_name:
+                var_values.append(config_var.value)
+
+        return var_values
+
+    @property
+    def config_txt_path(self) -> str:
+        return self._config_txt_path
+
+
 def configure_avahi_daemon(action: ConfigActions):
     return_value = simple_systemd(action, "avahi-daemon.service")
 
@@ -187,3 +279,6 @@ if __name__ == "__main__":
     print("CM Type:        ", rc.cm_type.name)
     print("With wifi:      ", rc.with_wifi)
     print("With con-bridge:", rc.with_con_bridge)
+
+    config_txt = ConfigTxt()
+    print("Config file:    ", config_txt.config_txt_path)