Refactor flags, add run() for better extensibility (#115)

main.go

@@ -13,54 +13,65 @@ import (
 	"github.com/matryer/moq/pkg/moq"
 )
 
-func main() {
-	var err error
-	defer func() {
-		if err != nil {
-			fmt.Fprintln(os.Stderr, err)
-			flag.Usage()
-			os.Exit(1)
-
+type userFlags struct {
+	outFile string
+	pkgName string
+	args    []string
 }
-	}()
-	var (
-		outFile = flag.String("out", "", "output file (default stdout)")
-		pkgName = flag.String("pkg", "", "package name (default will infer)")
-	)
+
+func main() {
+	var flags userFlags
+	flag.StringVar(&flags.outFile, "out", "", "output file (default stdout)")
+	flag.StringVar(&flags.pkgName, "pkg", "", "package name (default will infer)")
+
 	flag.Usage = func() {
 		fmt.Println(`moq [flags] destination interface [interface2 [interface3 [...]]]`)
 		flag.PrintDefaults()
 		fmt.Println(`Specifying an alias for the mock is also supported with the format 'interface:alias'`)
 		fmt.Println(`Ex: moq -pkg different . MyInterface:MyMock`)
 	}
+
 	flag.Parse()
-	args := flag.Args()
-	if len(args) < 2 {
-		err = errors.New("not enough arguments")
-		return
+	flags.args = flag.Args()
+
+	if err := run(flags); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		flag.Usage()
+		os.Exit(1)
 	}
-	destination := args[0]
-	args = args[1:]
+}
+
+func run(flags userFlags) error {
+	if len(flags.args) < 2 {
+		return errors.New("not enough arguments")
+	}
+
 	var buf bytes.Buffer
-	var out io.Writer
-	out = os.Stdout
-	if len(*outFile) > 0 {
+	var out io.Writer = os.Stdout
+	if flags.outFile != "" {
 		out = &buf
 	}
-	m, err := moq.New(destination, *pkgName)
+
+	destination := flags.args[0]
+	args := flags.args[1:]
+	m, err := moq.New(destination, flags.pkgName)
 	if err != nil {
-		return
+		return err
 	}
-	err = m.Mock(out, args...)
-	if err != nil {
-		return
+
+	if err = m.Mock(out, args...); err != nil {
+		return err
 	}
+
+	if flags.outFile == "" {
+		return nil
+	}
+
 	// create the file
-	if len(*outFile) > 0 {
-		err = os.MkdirAll(filepath.Dir(*outFile), 0755)
+	err = os.MkdirAll(filepath.Dir(flags.outFile), 0755)
 	if err != nil {
-			return
-		}
-		err = ioutil.WriteFile(*outFile, buf.Bytes(), 0644)
+		return err
 	}
+
+	return ioutil.WriteFile(flags.outFile, buf.Bytes(), 0644)
 }