refactor preset validation

cmd/root.go

@@ -17,6 +17,7 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 package cmd
 
 import (
+	"errors"
 	"log"
 	"os"
 
@@ -27,6 +28,23 @@ import (
 var presets []string
 var transition bool
 
+/*
+ * validatePresets performs some basic checks on the presets passed in and
+ * returns an error if it finds a problem.
+ */
+func validatePresets() error {
+	for _, p := range presets {
+		info, err := os.Stat(p)
+		if err != nil {
+			return err
+		} else if info.IsDir() {
+			return errors.New("preset " + p + " is a directory")
+		}
+	}
+
+	return nil
+}
+
 /*
  * handleWindowEvent handles window events like resizing.
  */
@@ -86,13 +104,9 @@ func milkbucket(cmd *cobra.Command, args []string) {
 	}
 	defer sdl.Quit()
 
-	for _, p := range presets {
-		info, err := os.Stat(p)
-		if err != nil {
-			panic(err)
-		} else if info.IsDir() {
-			panic("preset " + p + " is a directory")
-		}
+	err = validatePresets()
+	if err != nil {
+		panic(err)
 	}
 
 	m, err := newMilkDropWindow(800, 600, presets)