package main

import (
	"bufio"
	"crypto/tls"
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"strings"

	"gopkg.in/ldap.v2"
)

var (
	configFile string
	domain     string
	host       string

	ldap_uri             string
	ldap_default_bind_dn string
	ldap_default_authtok string
	ldap_search_base     string
)

type IP struct {
	Query string
}

func init() {
	test, err := os.Hostname()
	if err == nil {
		host = test
	}
	flag.StringVar(&configFile, "c", "/etc/sssd/sssd.conf", "Path to SSSD Config.")
	flag.StringVar(&host, "h", "", "Host ID for DNS (relativeDomainName)")
	flag.StringVar(&domain, "d", "", "Domain for DNS (zoneName)")
	flag.Parse()
}

func main() {
	log.Printf("Using %+v as config file path", configFile)

	file, err := os.Open(configFile)
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	// optionally, resize scanner's capacity for lines over 64K, see next example
	for scanner.Scan() {
		line := scanner.Text()
		mod := &ldap_uri
		switch {
		case strings.Contains(line, "ldap_uri"):
			mod = &ldap_uri
		case strings.Contains(line, "ldap_default_bind_dn"):
			mod = &ldap_default_bind_dn
		case strings.Contains(line, "ldap_default_authtok"):
			mod = &ldap_default_authtok
		case strings.Contains(line, "ldap_search_base"):
			mod = &ldap_search_base

		default:
			continue
		}
		*mod = strings.Split(line, "= ")[1]

	}

	if err := scanner.Err(); err != nil {
		log.Fatal(err)
	}
	log.Printf("Connecting to %s", ldap_uri)
	ldap_uri = strings.ReplaceAll(ldap_uri, "ldap://", "")
	l, err := ldap.Dial("tcp", ldap_uri)
	if err != nil {
		log.Fatal(err)
	}
	defer l.Close()
	log.Printf("Connected to %s, reconnecting with TLS", ldap_uri)
	// Reconnect with TLS
	err = l.StartTLS(&tls.Config{InsecureSkipVerify: true})
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("Binding as %s", ldap_default_bind_dn)
	// First bind with a read only user
	err = l.Bind(ldap_default_bind_dn, ldap_default_authtok)
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("Connected as read-only user, searching for DNS Record")
	// Search for the given username
	searchRequest := ldap.NewSearchRequest(
		fmt.Sprintf("zoneName=%s,cn=dns,%s", ldap.EscapeFilter(domain), ldap.EscapeFilter(ldap_search_base)),
		ldap.ScopeWholeSubtree, ldap.NeverDerefAliases, 0, 0, false,
		fmt.Sprintf("(relativeDomainName=%s)", ldap.EscapeFilter(host)),
		[]string{"dn","aRecord"},
		nil,
	)

	sr, err := l.Search(searchRequest)
	if err != nil {
		log.Fatal(err)
	}

	if len(sr.Entries) != 1 {
		log.Fatalf("Host does not exist or too many entries returned (%+v)", len(sr.Entries))
	}
	log.Printf("Record found for %s.%s: %+v", host, domain, sr.Entries[0])
	newIp := getip2()
	if sr.Entries[0].GetAttributeValue("aRecord") == newIp {
		log.Println("New IP is same as old IP, exiting gracefully.")
		return
	}
	req := ldap.NewModifyRequest(sr.Entries[0].DN)

	req.Replace("aRecord", []string{newIp})
	if err = l.Modify(req); err != nil {
		log.Fatalf("Failed to modify DN: %s\n", err)
	}
	log.Printf("Updated record successfully.")

}

func getip2() string {
	req, err := http.Get("http://ip-api.com/json/")
	if err != nil {
		return err.Error()
	}
	defer req.Body.Close()

	body, err := ioutil.ReadAll(req.Body)
	if err != nil {
		return err.Error()
	}

	var ip IP
	json.Unmarshal(body, &ip)
	log.Printf("Detected IP as %s", ip.Query)
	return ip.Query
}