use state machine to manage player state

core/model/player.go

@@ -4,3 +4,27 @@ type AudioDevice struct {
 	Name        string
 	Description string
 }
+
+type PlayerState int
+
+const (
+	PlayerStatePlaying PlayerState = iota
+	PlayerStateLoading
+	PlayerStateIdle
+)
+
+func (s PlayerState) NextState(next PlayerState) PlayerState {
+	if s == PlayerStatePlaying {
+		return next
+	}
+	if s == PlayerStateIdle {
+		return next
+	}
+	if s == PlayerStateLoading {
+		if next != PlayerStatePlaying {
+			return PlayerStateLoading
+		}
+		return next
+	}
+	return next
+}