fbd-feedback-base: Add fbd_feedback_is_available ()

This allows to check if a feedback type is available
at all.

src/fbd-feedback-base.c

@@ -227,3 +227,28 @@ fbd_feedback_base_done (FbdFeedbackBase *self)
   priv->ended = TRUE;
   g_signal_emit (self, signals[SIGNAL_ENDED], 0);
 }
+
+/**
+ * fbd_feedback_available:
+ * @self: The feedback
+ *
+ * Whether this feedback type is available at all. This can be %FALSE e.g.
+ * due to missing hardware.
+ *
+ * Returns: %FALSE if the feedback type is not available at all %TRUE if unsure
+ * or available.
+ */
+gboolean
+fbd_feedback_is_available (FbdFeedbackBase *self)
+{
+  FbdFeedbackBaseClass *klass;
+
+  g_return_val_if_fail (FBD_IS_FEEDBACK_BASE (self), FALSE);
+
+  klass = FBD_FEEDBACK_BASE_GET_CLASS (self);
+  if (klass->is_available)
+    return klass->is_available (self);
+  else
+    return TRUE;
+}
+

src/fbd-feedback-base.h

@@ -17,8 +17,9 @@ struct _FbdFeedbackBaseClass
 {
   GObjectClass parent_class;
 
-  void (*run) (FbdFeedbackBase *self);
+  void     (*run) (FbdFeedbackBase *self);
-  void (*end) (FbdFeedbackBase *self);
+  void     (*end) (FbdFeedbackBase *self);
+  gboolean (*is_available) (FbdFeedbackBase *self);
 };
 
 
@@ -27,5 +28,6 @@ void         fbd_feedback_run (FbdFeedbackBase *self);
 void         fbd_feedback_end (FbdFeedbackBase *self);
 gboolean     fbd_feedback_get_ended (FbdFeedbackBase *self);
 void         fbd_feedback_base_done (FbdFeedbackBase *self);
+gboolean     fbd_feedback_is_available (FbdFeedbackBase *self);
 
 G_END_DECLS