Convert oracle html grammars to antlr4

convert.go

package main

import (
	"errors"
	"fmt"
	"io/ioutil"
	"os"
	"regexp"
	"strings"
)

func main() {
	fname := os.Args[1]
	test := true
	if len(os.Args) == 2 {
		test = false
	}
	grmr, grmrfname := processFile(fname)
	if test {
		fmt.Printf("%s", grmr)
	} else {
		ioutil.WriteFile(grmrfname, []byte(grmr), 0644)
		err := os.Remove(fname)
		check(err)
	}
}

func processFile(fname string) (string, string) {
	dat, err := ioutil.ReadFile(fname)
	check(err)
	grmr, err := to_grmr(string(dat))
	check(err)
	grmr_name, err := to_grmr_name(fname)
	check(err)
	grmr = strings.Replace(grmr, "'", " '\\'' ", -1)
	grmr = strings.Replace(grmr, ">", " '>' ", -1)
	grmr = strings.Replace(grmr, ";", " ';' ", -1)
	grmr = fmt.Sprintf("grammar %s;\n\n%s : %s\t;\n", grmr_name, grmr_name, grmr)
	grmr = strings.Replace(grmr, "<b>", " '", -1)
	grmr = strings.Replace(grmr, "</b>", "' ", -1)
	grmr = strings.Replace(grmr, "(", " '(' ", -1)
	grmr = strings.Replace(grmr, ")", " ')' ", -1)
	grmr = strings.Replace(grmr, ",", " ',' ", -1)
	grmr = strings.Replace(grmr, "[", "(", -1)
	grmr = strings.Replace(grmr, "]", ")? ", -1)
	grmr = strings.Replace(grmr, "...", "", -1)
	grmr = strings.Replace(grmr, "{", "(", -1)
	grmr = strings.Replace(grmr, "}", ")", -1)
	// a lone *
	r := regexp.MustCompile("[^*][+]")
	grmr = r.ReplaceAllString(grmr, " '+' ")
	// a lone /
	r = regexp.MustCompile("[^*]/[^*]")
	grmr = r.ReplaceAllString(grmr, " '/' ")
	grmr = strings.Replace(grmr, "/*+", " '/*+' ", -1)
	grmr = strings.Replace(grmr, "*/", " '*/' ", -1)
	grmr = strings.Replace(grmr, ".", " '.' ", -1)

	return grmr, grmr_name + ".g4"
}

// pulls the pre tag out of the html file.
func to_grmr(htm string) (string, error) {
	start := strings.Index(htm, "<pre>")
	end := strings.Index(htm, "</pre>")
	if start == -1 || end == -1 {
		return "", errors.New("not a valid html: missing pre")
	}
	start = start + 6
	if end <= start {
		return "", errors.New("nothing in pre tags")
	}
	return htm[start:end], nil
}

func to_grmr_name(fname string) (string, error) {
	if !strings.HasSuffix(fname, ".htm") {
		return "", errors.New("fname is not a .htm ")
	}
	return fname[:len(fname)-4], nil
}

func check(e error) {
	if e != nil {
		panic(e)
	}
}