split main.go into modules, add --version flag

util.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+)
+
+type packageFlags struct {
+	dryRun bool
+}
+
+func parsePackageFlags(args []string) (packageFlags, string, error) {
+	flags := packageFlags{}
+	var pkg string
+	for _, arg := range args {
+		if arg == "--dry-run" {
+			flags.dryRun = true
+			continue
+		}
+		if strings.HasPrefix(arg, "-") {
+			return flags, "", fmt.Errorf("unknown flag %q", arg)
+		}
+		if pkg != "" {
+			return flags, "", errors.New("too many arguments")
+		}
+		pkg = arg
+	}
+	if pkg == "" {
+		return flags, "", errors.New("missing package")
+	}
+	return flags, pkg, nil
+}
+
+var stdinReader *bufio.Reader
+
+func newReader() *bufio.Reader {
+	if stdinReader == nil {
+		stdinReader = bufio.NewReader(os.Stdin)
+	}
+	return stdinReader
+}
+
+func promptWithDefault(label, def string) string {
+	reader := newReader()
+	if def != "" {
+		fmt.Printf("%s [%s]: ", label, def)
+	} else {
+		fmt.Printf("%s: ", label)
+	}
+
+	text, _ := reader.ReadString('\n')
+	text = strings.TrimSpace(text)
+	if text == "" {
+		return def
+	}
+	return text
+}
+
+func promptYesNo(message string, def bool) (bool, error) {
+	reader := newReader()
+	defLabel := "y/N"
+	if def {
+		defLabel = "Y/n"
+	}
+	fmt.Printf("%s [%s]: ", message, defLabel)
+	text, err := reader.ReadString('\n')
+	if err != nil {
+		return false, err
+	}
+	text = strings.TrimSpace(strings.ToLower(text))
+	if text == "" {
+		return def, nil
+	}
+	return text == "y" || text == "yes", nil
+}