jsontoml: port to v2 (#726)

Fixes #719

internal/cli/cli.go

@@ -0,0 +1,37 @@
+package cli
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"os"
+)
+
+type ConvertFn func(r io.Reader, w io.Writer) error
+
+func Execute(usage string, fn ConvertFn) {
+	flag.Usage = func() { fmt.Fprintf(os.Stderr, usage) }
+	flag.Parse()
+	os.Exit(processMain(flag.Args(), os.Stdin, os.Stdout, os.Stderr, fn))
+}
+
+func processMain(files []string, input io.Reader, output, error io.Writer, f ConvertFn) int {
+	err := run(files, input, output, f)
+	if err != nil {
+		fmt.Fprintln(error, err.Error())
+		return -1
+	}
+	return 0
+}
+
+func run(files []string, input io.Reader, output io.Writer, convert ConvertFn) error {
+	if len(files) > 0 {
+		f, err := os.Open(files[0])
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+		input = f
+	}
+	return convert(input, output)
+}