package main
// pemdecode ver. 1.0
// coded by Kenar
import (
	. "fmt"
	"os"
	"encoding/pem"
	"strconv"
)

var usage = `usage: pemdecode cert.pem [n]
   n is 1,2,...
   n: certificate number in cert.pem to be decoded
   if n is not given, all certificates will be decoded`

func Error(s interface{}){
	Fprintln(os.Stderr,s)
	os.Exit(1)
}

func check(err error) {
	if err != nil {
		Error(err)
	}
}

const (
  max = 10
)

func main() {
	var pb [max]*pem.Block
	var n int
	var err error
	var bs []byte
	args := os.Args[1:]
	if len(args) != 1 && len(args) != 2{
		Error(usage)
	}

	bs,err = os.ReadFile(args[0])
	check(err)

	for k:=0; len(bs) > 0 ; k++ {
		pb[k],bs = pem.Decode(bs)
	}

	if len(args) == 2 {
		n,err = strconv.Atoi(args[1])
		check(err)
		if n < 1 || n >= max || pb[n-1] == nil {
			Error(usage)
		}
		Printf("%s", pb[n-1].Bytes)
		return
	}

	for k:=0; pb[k] != nil; k++ {
		if k != 0 {
			Println()
		}
		Printf("%s", pb[k].Bytes)
	}
}