feat: show no-WFB kiosk fallback only while video absent (#2)

cmd/groundstation-display/main.go

@@ -18,10 +18,15 @@ import (
 
 // buildTarget selects the target-specific opener and template. Each target
 // owns its own backend and layouts; there is no shared global template.
+// buildTarget wires one shared video presence signal into both the opener
+// (which observes the video output lifecycle) and the fallback template
+// (which shows or hides itself from it).
 func buildTarget(name string) (display.Opener, display.Template, error) {
 	switch name {
 	case "x11":
-		return display.X11Opener{}, display.NewStatusTemplate("Brak polaczenia WFB"), nil
+		video := display.NewVideoPresence()
+		return display.X11Opener{Video: video},
+			display.NewFallbackTemplate(video, "Brak połączenia WFB"), nil
 	default:
 		return nil, nil, fmt.Errorf("unknown display target %q (supported: x11)", name)
 	}

cmd/groundstation-display/main_test.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"testing"
+
+	"git.piksar.eu/piotr/groundstation/internal/display"
+)
+
+type recordingCanvas struct {
+	width, height   int
+	lines           []string
+	clears, flushes int
+}
+
+func (c *recordingCanvas) Size() (int, int) { return c.width, c.height }
+func (c *recordingCanvas) Clear()           { c.clears++ }
+func (c *recordingCanvas) Text(_, _ int, message string) {
+	c.lines = append(c.lines, message)
+}
+func (c *recordingCanvas) Flush() { c.flushes++ }
+
+func TestBuildTargetWiresSharedVideoPresenceToFallback(t *testing.T) {
+	opener, template, err := buildTarget("x11")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	x11, ok := opener.(display.X11Opener)
+	if !ok {
+		t.Fatalf("opener %T must be the X11 target", opener)
+	}
+	if x11.Video == nil {
+		t.Fatal("x11 opener must observe the video presence signal")
+	}
+
+	canvas := &recordingCanvas{width: 800, height: 600}
+	template.Draw(canvas)
+	if len(canvas.lines) != 1 || canvas.lines[0] != "Brak połączenia WFB" {
+		t.Fatalf("lines=%q want the exact fallback text", canvas.lines)
+	}
+
+	// The opener and the template must share one presence signal so the
+	// video lifecycle observed by the session drives the fallback.
+	x11.Video.SetActive(true)
+	canvas.lines = nil
+	template.Draw(canvas)
+	if len(canvas.lines) != 0 {
+		t.Fatalf("lines=%q must disappear while video is present", canvas.lines)
+	}
+
+	x11.Video.SetActive(false)
+	canvas.lines = nil
+	template.Draw(canvas)
+	if len(canvas.lines) != 1 || canvas.lines[0] != "Brak połączenia WFB" {
+		t.Fatalf("lines=%q want the fallback back after video end", canvas.lines)
+	}
+}
+
+func TestBuildTargetRejectsUnknownTarget(t *testing.T) {
+	if _, _, err := buildTarget("hdmi-mirror"); err == nil {
+		t.Fatal("unknown target must fail")
+	}
+}