Add video driver state management

pkg/driver/camera_linux.go

@@ -96,15 +96,17 @@ func (c *camera) Start(setting VideoSetting, cb DataCb) error {
 		case *webcam.Timeout:
 			continue
 		default:
-			return err
+			// Camera has been stopped. We don't need to return an error.
+			return nil 
 		}
 
 		frame, err := c.cam.ReadFrame()
 		if err != nil {
-			// TODO: Add a better error handling
+			// Camera has been stopped. We don't need to return an error.
-			return err
+			return nil
 		}
 
+		// Frame is not ready.
 		if len(frame) == 0 {
 			continue
 		}

pkg/driver/wrapper.go

@@ -2,6 +2,8 @@ package driver
 
 import uuid "github.com/satori/go.uuid"
 
+import "fmt"
+
 func wrapAdapter(a Adapter) Driver {
 	var d Driver
 	id := uuid.NewV4().String()
@@ -37,6 +39,64 @@ func (w *videoAdapterWrapper) Status() State {
 	return w.state
 }
 
+func (w *videoAdapterWrapper) Open() error {
+	if w.state != StateClosed {
+		return fmt.Errorf("invalid state: driver is already opened")
+	}
+
+	err := w.VideoAdapter.Open()
+	if err == nil {
+		w.state = StateOpened
+	}
+	return err
+}
+
+func (w *videoAdapterWrapper) Close() error {
+	err := w.VideoAdapter.Close()
+	if err == nil {
+		w.state = StateClosed
+	}
+	return err
+}
+
+func (w *videoAdapterWrapper) Start(setting VideoSetting, cb DataCb) error {
+	if w.state == StateClosed {
+		return fmt.Errorf("invalid state: driver hasn't been opened")
+	}
+
+	if w.state == StateStarted {
+		return fmt.Errorf("invalid state: driver has been started")
+	}
+
+	prevState := w.state
+	w.state = StateOpened
+	err := w.VideoAdapter.Start(setting, cb)
+	if err != nil {
+		w.state = prevState
+	}
+	return err
+}
+
+func (w *videoAdapterWrapper) Stop() error {
+	if w.state != StateStarted {
+		return fmt.Errorf("invalid state: driver hasn't been started")
+	}
+
+	err := w.VideoAdapter.Stop()
+	if err == nil {
+		w.state = StateStopped
+	}
+	return err
+}
+
+func (w *videoAdapterWrapper) Settings() []VideoSetting {
+	if w.state == StateClosed {
+		return nil
+	}
+
+	return w.VideoAdapter.Settings()
+}
+
 // TODO: Add state validation
 type audioAdapterWrapper struct {
 	AudioAdapter