From 4ef16048adb9845660b8c95163192f8116b16eb2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesko=20Ansch=C3=BCtz?= <jesko@linuxmuster.net>
Date: Thu, 26 Mar 2026 23:07:14 +0100
Subject: [PATCH] feat(agent): displaycontroller Package (xset DPMS)

---
 .../internal/displaycontroller/controller.go  | 74 +++++++++++++++++++
 .../displaycontroller/controller_test.go      | 18 +++++
 2 files changed, 92 insertions(+)
 create mode 100644 player/agent/internal/displaycontroller/controller.go
 create mode 100644 player/agent/internal/displaycontroller/controller_test.go

diff --git a/player/agent/internal/displaycontroller/controller.go b/player/agent/internal/displaycontroller/controller.go
new file mode 100644
index 0000000..66bf8a0
--- /dev/null
+++ b/player/agent/internal/displaycontroller/controller.go
@@ -0,0 +1,74 @@
+// Package displaycontroller steuert das physische Display per xset DPMS.
+package displaycontroller
+
+import (
+	"fmt"
+	"log/slog"
+	"os/exec"
+	"sync"
+)
+
+// Controller führt xset-Befehle aus und verfolgt den letzten Display-Zustand.
+// onStateChange wird nach jeder erfolgreichen Ausführung mit dem neuen Zustand
+// aufgerufen (z. B. um ihn per MQTT zu publizieren). Darf nil sein.
+type Controller struct {
+	display       string
+	screenSlug    string
+	onStateChange func(screenSlug, state string)
+	mu            sync.Mutex
+	currentState  string
+}
+
+// New erstellt einen Controller. display ist der Wert der DISPLAY-Env-Var (z. B. ":0").
+func New(display, screenSlug string, onStateChange func(screenSlug, state string)) *Controller {
+	return &Controller{
+		display:       display,
+		screenSlug:    screenSlug,
+		onStateChange: onStateChange,
+		currentState:  "unknown",
+	}
+}
+
+// Execute führt eine Display-Aktion aus. Bekannte Aktionen: "display_on", "display_off".
+func (c *Controller) Execute(action string) {
+	switch action {
+	case "display_on":
+		if err := c.runXset("on"); err != nil {
+			slog.Error("display_on failed", "err", err)
+			return
+		}
+		c.setState("on")
+	case "display_off":
+		if err := c.runXset("off"); err != nil {
+			slog.Error("display_off failed", "err", err)
+			return
+		}
+		c.setState("off")
+	default:
+		slog.Warn("unknown display action", "action", action)
+	}
+}
+
+// State gibt den zuletzt gesetzten Display-Zustand zurück: "on", "off" oder "unknown".
+func (c *Controller) State() string {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.currentState
+}
+
+func (c *Controller) runXset(arg string) error {
+	out, err := exec.Command("xset", "-display", c.display, "dpms", "force", arg).CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("xset dpms force %s: %w (output: %s)", arg, err, out)
+	}
+	return nil
+}
+
+func (c *Controller) setState(state string) {
+	c.mu.Lock()
+	c.currentState = state
+	c.mu.Unlock()
+	if c.onStateChange != nil {
+		go c.onStateChange(c.screenSlug, state)
+	}
+}
diff --git a/player/agent/internal/displaycontroller/controller_test.go b/player/agent/internal/displaycontroller/controller_test.go
new file mode 100644
index 0000000..ef6ec29
--- /dev/null
+++ b/player/agent/internal/displaycontroller/controller_test.go
@@ -0,0 +1,18 @@
+package displaycontroller
+
+import "testing"
+
+func TestNew_initialState(t *testing.T) {
+	c := New(":0", "test-screen", nil)
+	if got := c.State(); got != "unknown" {
+		t.Fatalf("initial state = %q, want %q", got, "unknown")
+	}
+}
+
+func TestExecute_unknownAction(t *testing.T) {
+	c := New(":0", "test-screen", nil)
+	c.Execute("invalid_action")
+	if got := c.State(); got != "unknown" {
+		t.Fatalf("state after unknown action = %q, want %q", got, "unknown")
+	}
+}