Improved command line parsing, started on json-based parsing instructions

cmd/sutron/main.go

@@ -1,26 +1,63 @@
 package main
 
 import (
-	"git.binarythought.com/cdramey/sutron"
-	"fmt"
 	"bytes"
+	"flag"
+	"fmt"
+	"encoding/json"
+	"git.binarythought.com/cdramey/sutron"
 	"io/ioutil"
 	"os"
 )
 
+type ParserConfig struct {
+	ParserType string `json:"parser_type"`
+}
+
 func main() {
-	if len(os.Args) < 2 {
+	flags := flag.NewFlagSet("sutron", flag.ExitOnError)
+	flags.SetOutput(os.Stdout)
+	flags.Usage = func() {
+		fmt.Fprintf(flags.Output(),
+			"Usage: %s [OPTION] <files> ...\nOptions:\n",
+			os.Args[0])
+		flags.PrintDefaults()
+	}
+
+	jsonfn := flags.String("json", "sutron.json",
+		"json parser definition file name")
+
+	flags.Parse(os.Args[1:])
+
+	if flags.NArg() < 1 {
+		fmt.Fprintf(os.Stderr, "files parameter cannot be empty\n")
+		os.Exit(1)
+	}
+
+	jsonsrc, err := ioutil.ReadFile(*jsonfn)
+	if err != nil {
 		fmt.Fprintf(os.Stderr,
-			"required argument missing\n")
+			"error reading \"%s\": %s\n",
+			os.Args[1], err.Error())
+	}
+
+	var pcfg ParserConfig
+	err = json.Unmarshal(jsonsrc, &pcfg)
+	if err != nil {
+		fmt.Fprintf(os.Stderr,
+			"parser config error: %s\n", err.Error())
 		os.Exit(1)
 	}
 
+	fmt.Printf("Parser type: %s\n", pcfg.ParserType)
+
+	for _, fn := range flags.Args() {
 		var raw []byte
 		var err error
-	if os.Args[1] == "-" {
+		if fn == "-" {
 			raw, err = ioutil.ReadAll(os.Stdin)
 		} else {
-		raw, err = ioutil.ReadFile(os.Args[1])
+			raw, err = ioutil.ReadFile(fn)
 		}
 		if err != nil {
 			fmt.Fprintf(os.Stderr,
@@ -43,3 +80,4 @@ func main() {
 			fmt.Printf("Sutron Voltage: %s\n", string(sutrondata.Voltage))
 		}
 	}
+}