brightness: add udev monitor, bind OSDs to netlink events

fixes #863

core/internal/server/brightness/udev.go

@@ -0,0 +1,148 @@
+package brightness
+
+import (
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"github.com/AvengeMedia/DankMaterialShell/core/internal/log"
+	"github.com/pilebones/go-udev/netlink"
+)
+
+type UdevMonitor struct {
+	stop chan struct{}
+}
+
+func NewUdevMonitor(manager *Manager) *UdevMonitor {
+	m := &UdevMonitor{
+		stop: make(chan struct{}),
+	}
+
+	go m.run(manager)
+	return m
+}
+
+func (m *UdevMonitor) run(manager *Manager) {
+	conn := &netlink.UEventConn{}
+	if err := conn.Connect(netlink.UdevEvent); err != nil {
+		log.Errorf("Failed to connect to udev netlink: %v", err)
+		return
+	}
+	defer conn.Close()
+
+	matcher := &netlink.RuleDefinitions{
+		Rules: []netlink.RuleDefinition{
+			{Env: map[string]string{"SUBSYSTEM": "backlight"}},
+			{Env: map[string]string{"SUBSYSTEM": "leds"}},
+		},
+	}
+	if err := matcher.Compile(); err != nil {
+		log.Errorf("Failed to compile udev matcher: %v", err)
+		return
+	}
+
+	events := make(chan netlink.UEvent)
+	errs := make(chan error)
+	conn.Monitor(events, errs, matcher)
+
+	log.Info("Udev monitor started for backlight/leds events")
+
+	for {
+		select {
+		case <-m.stop:
+			return
+		case err := <-errs:
+			log.Errorf("Udev monitor error: %v", err)
+			return
+		case event := <-events:
+			m.handleEvent(manager, event)
+		}
+	}
+}
+
+func (m *UdevMonitor) handleEvent(manager *Manager, event netlink.UEvent) {
+	subsystem := event.Env["SUBSYSTEM"]
+	devpath := event.Env["DEVPATH"]
+
+	if subsystem == "" || devpath == "" {
+		return
+	}
+
+	sysname := filepath.Base(devpath)
+	action := string(event.Action)
+
+	switch action {
+	case "change":
+		m.handleChange(manager, subsystem, sysname)
+	case "add", "remove":
+		log.Debugf("Udev %s event: %s:%s - triggering rescan", action, subsystem, sysname)
+		manager.Rescan()
+	}
+}
+
+func (m *UdevMonitor) handleChange(manager *Manager, subsystem, sysname string) {
+	deviceID := subsystem + ":" + sysname
+
+	if manager.sysfsBackend == nil {
+		return
+	}
+
+	brightnessPath := filepath.Join(manager.sysfsBackend.basePath, subsystem, sysname, "brightness")
+	data, err := os.ReadFile(brightnessPath)
+	if err != nil {
+		log.Debugf("Udev change event for %s but failed to read brightness: %v", deviceID, err)
+		return
+	}
+
+	brightness, err := strconv.Atoi(strings.TrimSpace(string(data)))
+	if err != nil {
+		log.Debugf("Failed to parse brightness for %s: %v", deviceID, err)
+		return
+	}
+
+	manager.handleUdevBrightnessChange(deviceID, brightness)
+}
+
+func (m *UdevMonitor) Close() {
+	close(m.stop)
+}
+
+func (m *Manager) handleUdevBrightnessChange(deviceID string, rawBrightness int) {
+	if m.sysfsBackend == nil {
+		return
+	}
+
+	dev, err := m.sysfsBackend.GetDevice(deviceID)
+	if err != nil {
+		log.Debugf("Udev event for unknown device %s: %v", deviceID, err)
+		return
+	}
+
+	percent := m.sysfsBackend.ValueToPercent(rawBrightness, dev, false)
+
+	m.stateMutex.Lock()
+	var found bool
+	for i, d := range m.state.Devices {
+		if d.ID != deviceID {
+			continue
+		}
+		found = true
+		if d.Current == rawBrightness {
+			m.stateMutex.Unlock()
+			return
+		}
+		m.state.Devices[i].Current = rawBrightness
+		m.state.Devices[i].CurrentPercent = percent
+		break
+	}
+	m.stateMutex.Unlock()
+
+	if !found {
+		log.Debugf("Udev event for device not in state: %s", deviceID)
+		return
+	}
+
+	log.Debugf("Udev brightness change: %s -> %d (%d%%)", deviceID, rawBrightness, percent)
+	m.broadcastDeviceUpdate(deviceID)
+}