package main

import (
	"bytes"
	"fmt"
	"net"
	"os/exec"
	"strings"
)

func createQuery(data userData, addr net.IP, deleteRecord bool) string {
	var query strings.Builder

	query.WriteString(fmt.Sprintf("key %s\n", data.tsigkey))
	query.WriteString(fmt.Sprintf("server %s\n", data.nameserver))
	query.WriteString(fmt.Sprintf("zone %s\n", data.zonename))
	if deleteRecord {
		query.WriteString(fmt.Sprintf("update delete %s. A\n", data.hostname))
	}
	query.WriteString(fmt.Sprintf("update add %s. A %s\n", data.hostname,
								  addr.String()))
	query.WriteString("show\n")
	query.WriteString("send\n")

	return query.String()
}

func queryNameserver(query string) error {
	var (
		stdout bytes.Buffer
		stderr bytes.Buffer
	)

	cmd := exec.Command("knsupdate", "-v")
	cmd.Stdin = strings.NewReader(query)
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr
	err := cmd.Run()
	fmt.Printf(stdout.String())
	fmt.Printf(stderr.String())

	return err
}

func updateNameserver(data userData, addr net.IP) (bool, error) {
	updateRecord := true
	deleteRecord := true

	addrs, err := net.LookupIP(data.hostname)
	if err != nil {
		deleteRecord = false
	} else {
		for _, ip := range addrs {
			if ip.Equal(addr) {
				updateRecord = false
				break
			}
		}
	}
	if !updateRecord {
		return false, nil
	} else {
		query := createQuery(data, addr, deleteRecord)
		err = queryNameserver(query)
		if err != nil {
			return true, err
		}
		return true, nil
	}
}