Query UPower's OnBattery property directly.

On some systems, the name of the battery or the adapter may be different. The code assumes
the adapter is called "line_power_AC" and the battery "BAT0" but in my system both are different.

UPower has the OnBattery property which we can query and this is more robust. Additionally, we
can do it directly throuth the dbus API without invoking a sub-process.

throttled.py

@@ -310,24 +310,12 @@ def is_on_battery(config):
                 return not bool(int(f.read()))
         raise
     except:
-        warning('No valid Sysfs_Power_Path found! Trying upower method #1')
+        warning('No valid Sysfs_Power_Path found! Trying upower method')
     try:
-        out = subprocess.check_output(('upower', '-i', '/org/freedesktop/UPower/devices/line_power_AC'))
-        res = re.search(rb'online:\s+(yes|no)', out).group(1).decode().strip()
-        if res == 'yes':
-            return False
-        elif res == 'no':
-            return True
-        raise
-    except:
-        warning('Trying upower method #2')
-    try:
-        out = subprocess.check_output(('upower', '-i', '/org/freedesktop/UPower/devices/battery_BAT0'))
-        res = re.search(rb'state:\s+(.+)', out).group(1).decode().strip()
-        if res == 'discharging':
-            return True
-        elif res in ('fully-charged', 'charging', 'pending-charge'):
-            return False
+        bus = dbus.SystemBus()
+        proxy = bus.get_object('org.freedesktop.UPower', '/org/freedesktop/UPower')
+        iface = dbus.Interface(proxy, 'org.freedesktop.DBus.Properties')
+        return iface.Get('org.freedesktop.UPower', 'OnBattery')
     except:
         pass
 
@@ -974,6 +962,9 @@ def main():
 
     test_msr_rw_capabilities()
 
+    DBusGMainLoop(set_as_default=True)
+    bus = dbus.SystemBus()
+
     log('[I] Loading config file.')
     config = load_config()
     power['source'] = 'BATTERY' if is_on_battery(config) else 'AC'
@@ -1003,15 +994,10 @@ def main():
             undervolt(config)
             set_icc_max(config)
 
-    def handle_ac_callback(*args):
-        try:
-            power['source'] = 'BATTERY' if args[1]['Online'] == 0 else 'AC'
+    def handle_ac_callback(if_name, changed, invalidated):
+        if "OnBattery" in changed:
             power['method'] = 'dbus'
-        except:
-            power['method'] = 'polling'
-
-    DBusGMainLoop(set_as_default=True)
-    bus = dbus.SystemBus()
+            power['source'] = 'BATTERY' if bool(changed['OnBattery']) else 'AC'
 
     # add dbus receiver only if undervolt/IccMax is enabled in config
     if any(
@@ -1024,7 +1010,7 @@ def main():
         handle_ac_callback,
         signal_name="PropertiesChanged",
         dbus_interface="org.freedesktop.DBus.Properties",
-        path="/org/freedesktop/UPower/devices/line_power_AC",
+        path="/org/freedesktop/UPower",
     )
 
     log('[I] Starting main loop.')