added mpris (linux media player controls) support

backend/mediacontrols/mediacontrols.go

@@ -0,0 +1,63 @@
+// Package mediacontrols provides OS media control integration.
+//
+// On Linux this registers a MPRIS2 D-Bus service so that desktop
+// environments, playerctl, and media keys can control playback and
+// see the currently playing track. Other platforms get a no-op stub.
+package mediacontrols
+
+// PlaybackState represents the current playback state for the OS.
+type PlaybackState int
+
+// Playback state values.
+const (
+	StateStopped PlaybackState = iota
+	StatePlaying
+	StatePaused
+)
+
+// Metadata holds track information to display in the OS media overlay.
+type Metadata struct {
+	Title       string
+	Artist      string
+	Album       string
+	ArtFilePath string // Absolute filesystem path to cover art.
+	DurationSec int
+}
+
+// Callbacks are invoked when the OS sends media commands.
+type Callbacks struct {
+	OnPlay      func()
+	OnPause     func()
+	OnPlayPause func()
+	OnStop      func()
+	OnNext      func()
+	OnPrevious  func()
+	OnSeek      func(positionSec int)
+	OnVolume    func(volume float64) // 0.0–1.0 linear scale.
+}
+
+// Handler manages the OS media control integration.
+type Handler interface {
+	// Init registers with the OS and wires incoming commands to
+	// the provided callbacks. It must be called once during startup.
+	Init(callbacks Callbacks) error
+
+	// UpdateMetadata pushes new track metadata to the OS overlay.
+	UpdateMetadata(meta Metadata)
+
+	// UpdatePlaybackState pushes the playback state and current
+	// position. The position is used as a new anchor; the OS
+	// interpolates from there while playing.
+	UpdatePlaybackState(state PlaybackState, positionSec int)
+
+	// NotifySeek signals that the user seeked to a new position.
+	// This is separate from UpdatePlaybackState because MPRIS
+	// emits a distinct Seeked signal for this.
+	NotifySeek(positionSec int)
+
+	// UpdateVolume pushes the current volume (0.0–1.0) to the OS.
+	UpdateVolume(volume float64)
+
+	// Close tears down the OS registration and releases resources.
+	Close()
+}