Add support for Konsole

This patch extends the themer to support KDE's Konsole as the adapter.
The implementation utilizes multiple Konsole profiles, each of which is
set with the desired theme, and the DBus integration to iterate over all
active Konsole sessions to set it.

When used in KDE environment, it's important to let the "no preference"
value fallback to "light". That's because [the daemon][1] handling theme
synchronization between KDE and GTK toolkits uses a different heuristics
to translate the KDE theme to its GTK counterpart. In such case, themer
receives two signals, and the table below represents the emitted values:

preference | xdg-desktop-portal-kde | xdg-desktop-portal-gtk
------------------------------------------------------------
none       | no-preference          | no-preference
dark       | prefers-dark           | prefers-dark
light      | prefers-light          | no-preference

During development, the signal emitted from the GTK's has been coming
after the one generated by KDE, essentially overriding it.

[1]: https://invent.kde.org/plasma/kde-gtk-config/-/blob/master/kded/gtkconfig.cpp?ref_type=heads#L209

cmd/themer/main.go

@@ -104,6 +104,11 @@ func main() {
 					if err != nil {
 						log.Printf("Executing the AlacrittyAdapter: %v", err)
 					}
+				case config.KonsoleAdapter:
+					err := adapter.ExecuteKonsoleAdapter(colorSchemePreference, a.(config.KonsoleAdapter))
+					if err != nil {
+						log.Printf("Executing the KonsoleAdapter: %v", err)
+					}
 				default:
 					log.Fatalf("Unknown adapter: %T", a)
 				}

internal/adapter/adapter.go

@@ -2,11 +2,15 @@ package adapter
 
 import (
 	"bytes"
+	"encoding/xml"
 	"fmt"
 	"github.com/d1823/themer/internal/config"
 	"github.com/d1823/themer/internal/freedesktop"
+	"github.com/godbus/dbus/v5"
+	"log"
 	"os"
 	"os/exec"
+	"strings"
 	"time"
 )
 
@@ -63,6 +67,74 @@ func ExecuteTmuxAdapter(preference freedesktop.ColorSchemePreference, config con
 	return nil
 }
 
+type Node struct {
+	XMLName xml.Name `xml:"node"`
+	Name    string   `xml:"name,attr"`
+	Nodes   []Node   `xml:"node"`
+}
+
+func ExecuteKonsoleAdapter(preference freedesktop.ColorSchemePreference, config config.KonsoleAdapter) error {
+	// NOTE: The connection returned by the dbus.SessionBus is shared.
+	//       Closing it here would mean the main package would no longer receive the signals it's waiting for.
+	conn, err := dbus.SessionBus()
+	if err != nil {
+		log.Fatalf("Failed to connect to the D-Bus session bus: %v", err)
+	}
+
+	var listedServices []string
+	err = conn.BusObject().Call("org.freedesktop.DBus.ListNames", 0).Store(&listedServices)
+	if err != nil {
+		log.Fatalf("Failed to list service names: %v", err)
+	}
+
+	var profileName string
+	switch preference {
+	case freedesktop.NoPreference:
+		profileName = config.NoPreferenceProfileName
+	case freedesktop.PreferDarkAppearance:
+		profileName = config.DarkProfileName
+	case freedesktop.PreferLightAppearance:
+		profileName = config.LightProfileName
+	default:
+		return fmt.Errorf("invalid preference: %v", preference)
+	}
+
+	var introspection string
+	for _, service := range listedServices {
+		if !strings.HasPrefix(service, "org.kde.konsole-") {
+			continue
+		}
+
+		err = conn.Object(service, "/Sessions").
+			Call("org.freedesktop.DBus.Introspectable.Introspect", 0).
+			Store(&introspection)
+		if err != nil {
+			log.Fatalf("Failed to introspect the service: %v", err)
+		}
+
+		var root Node
+		err = xml.Unmarshal([]byte(introspection), &root)
+		if err != nil {
+			log.Fatalf("Failed to parse the introspection: %v", err)
+		}
+
+		sessions := make(map[string]struct{})
+		for _, node := range root.Nodes {
+			sessions[fmt.Sprintf("/Sessions/%s", node.Name)] = struct{}{}
+		}
+
+		for session, _ := range sessions {
+			call := conn.Object(service, dbus.ObjectPath(session)).
+				Call("org.kde.konsole.Session.setProfile", 0, profileName)
+			if call.Err != nil {
+				log.Fatalf("Failed to set profile: %v", call.Err)
+			}
+		}
+	}
+
+	return nil
+}
+
 func runCmd(args []string) (string, string, error) {
 	tmux, err := exec.LookPath("tmux")
 	if err != nil {

internal/config/config.go

@@ -26,6 +26,14 @@ type AlacrittyAdapter struct {
 	AlacrittyConfigFile string `mapstructure:"alacritty_config_file"`
 }
 
+// KonsoleAdapter represents the Konsole adapter configuration.
+type KonsoleAdapter struct {
+	SymlinkAdapter          `mapstructure:",squash"`
+	NoPreferenceProfileName string `mapstructure:"no_preference_profile_name"`
+	DarkProfileName         string `mapstructure:"dark_profile_name"`
+	LightProfileName        string `mapstructure:"light_profile_name"`
+}
+
 // Configuration represents the top-level configuration structure.
 type Configuration struct {
 	Adapters []interface{} `json:"adapters"`
@@ -68,6 +76,12 @@ func (c *Configuration) UnmarshalJSON(data []byte) error {
 				return fmt.Errorf("failed to decode 'alacritty' adapter: %v", err)
 			}
 			c.Adapters = append(c.Adapters, alacritty)
+		case "konsole":
+			konsole := KonsoleAdapter{}
+			if err := mapstructure.Decode(adapter, &konsole); err != nil {
+				return fmt.Errorf("failed to decode 'konsole' adapter: %v", err)
+			}
+			c.Adapters = append(c.Adapters, konsole)
 		default:
 			return fmt.Errorf("unknown adapter type: %v", adapter["adapter"])
 		}