upower: Add 'low' and 'critical' CSS classes

Add secondary CSS class based on the 'warning_level' field reported by UPower
over D-Bus.  This makes it possible to add custom styling when the battery is
near empty.

include/modules/upower/upower.hpp

@@ -71,6 +71,7 @@ class UPower : public AModule {
   GDBusConnection *login1_connection;
   std::unique_ptr<UPowerTooltip> upower_tooltip;
   std::string lastStatus;
+  const char *lastWarningLevel;
   bool showAltText;
   bool showIcon = true;
   bool upowerRunning;

src/modules/upower/upower.cpp

@@ -8,6 +8,17 @@
 #include "gtkmm/tooltip.h"
 #include "util/gtk_icon.hpp"
 
+static const char* getDeviceWarningLevel(UpDeviceLevel level) {
+  switch (level) {
+    case UP_DEVICE_LEVEL_CRITICAL:
+      return "critical";
+    case UP_DEVICE_LEVEL_LOW:
+      return "low";
+    default:
+      return nullptr;
+  }
+}
+
 namespace waybar::modules::upower {
 UPower::UPower(const std::string& id, const Json::Value& config)
     : AModule(config, "upower", id),
@@ -306,6 +317,7 @@ auto UPower::update() -> void {
 
   UpDeviceKind kind;
   UpDeviceState state;
+  UpDeviceLevel level = UP_DEVICE_LEVEL_UNKNOWN;
   double percentage;
   gint64 time_empty;
   gint64 time_full;
@@ -318,7 +330,7 @@ auto UPower::update() -> void {
   if (displayDevice) {
     g_object_get(displayDevice, "kind", &kind, "state", &state, "percentage", &percentage,
                  "icon-name", &icon_name, "time-to-empty", &time_empty, "time-to-full", &time_full,
-                 NULL);
+                 "warning-level", &level, NULL);
     /* Every Device which is handled by Upower and which is not
      * UP_DEVICE_KIND_UNKNOWN (0) or UP_DEVICE_KIND_LINE_POWER (1) is a Battery
      */
@@ -338,6 +350,15 @@ auto UPower::update() -> void {
   }
   lastStatus = status;
 
+  const char* warning_level = getDeviceWarningLevel(level);
+  if (lastWarningLevel && box_.get_style_context()->has_class(lastWarningLevel)) {
+    box_.get_style_context()->remove_class(lastWarningLevel);
+  }
+  if (warning_level && !box_.get_style_context()->has_class(warning_level)) {
+    box_.get_style_context()->add_class(warning_level);
+  }
+  lastWarningLevel = warning_level;
+
   if (devices.size() == 0 && !displayDeviceValid && hideIfEmpty) {
     event_box_.set_visible(false);
     // Call parent update