package main

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

func requiresRRUpdate(entry *RRConfig, addr net.IP) bool {
	// TODO: use custom resolver to query authoritive nameserver instead of
	// local resolver
	addrs, err := net.LookupIP(entry.Recordname)
	if err != nil {
		log.Printf("dns lookup failed: %s", err)
		// enforce update, it's better than not trying at all
		return true
	}

	// check if the current ip matches
	for _, ip := range addrs {
		if ip.Equal(addr) {
			// the ip seems to be still up-to-date -> no update required
			return false
		}
	}
	return true
}

func updateRR(entry *RRConfig, addr net.IP) error {
	query := generateQuery(entry, addr)
	return executeQuery(query)
}

func generateQuery(entry *RRConfig, addr net.IP) string {
	var q strings.Builder

	fmt.Fprintf(&q, "key %s:%s %s\n", entry.Tsigalgo, entry.Tsigid, entry.Tsigkey)
	fmt.Fprintf(&q, "server %s\n", entry.Nameserver)
	fmt.Fprintf(&q, "zone %s\n", entry.Zonename)
	// TODO: check if addr is ipv4 or ipv6 (-> update A or AAAA)
	fmt.Fprintf(&q, "add %s. %d A %s\n", entry.Recordname, entry.Ttl, addr.String())
	fmt.Fprintf(&q, "send\n")

	return q.String()
}

func executeQuery(query string) error {
	cmd := exec.Command("knsupdate", "-v")
	cmd.Stdin = strings.NewReader(query)
	output, err := cmd.CombinedOutput()
	// TODO: is outputting stdout+stderr on failure even necessary?
	if err != nil {
		log.Printf("executeQuery failed: %s", output)
	}

	return err
}