// Copyright or © or Copr. happyDNS (2020)
//
// contact@happydns.org
//
// This software is a computer program whose purpose is to provide a modern
// interface to interact with DNS systems.
//
// This software is governed by the CeCILL license under French law and abiding
// by the rules of distribution of free software.  You can use, modify and/or
// redistribute the software under the terms of the CeCILL license as
// circulated by CEA, CNRS and INRIA at the following URL
// "http://www.cecill.info".
//
// As a counterpart to the access to the source code and rights to copy, modify
// and redistribute granted by the license, users are provided only with a
// limited warranty and the software's author, the holder of the economic
// rights, and the successive licensors have only limited liability.
//
// In this respect, the user's attention is drawn to the risks associated with
// loading, using, modifying and/or developing or reproducing the software by
// the user in light of its specific status of free software, that may mean
// that it is complicated to manipulate, and that also therefore means that it
// is reserved for developers and experienced professionals having in-depth
// computer knowledge. Users are therefore encouraged to load and test the
// software's suitability as regards their requirements in conditions enabling
// the security of their systems and/or data to be ensured and, more generally,
// to use and operate it in the same conditions as regards security.
//
// The fact that you are presently reading this means that you have had
// knowledge of the CeCILL license and that you accept its terms.

package ddns // import "happydns.org/sources/ddns"

import (
	"encoding/base64"
	"fmt"
	"net"
	"strings"
	"time"

	"github.com/miekg/dns"

	"git.happydns.org/happydns/model"
	"git.happydns.org/happydns/sources"
)

type DDNSServer struct {
	Server  string `json:"server,omitempty" happydns:"label=Server,placeholder=127.0.0.1"`
	KeyName string `json:"keyname,omitempty" happydns:"label=Key Name,placeholder=ddns.,required"`
	KeyAlgo string `json:"algorithm,omitempty" happydns:"label=Key Algorithm,default=hmac-sha256.,choices=hmac-md5.sig-alg.reg.int.;hmac-sha1.;hmac-sha224.;hmac-sha256.;hmac-sha384.;hmac-sha512.,required"`
	KeyBlob []byte `json:"keyblob,omitempty" happydns:"label=Secret Key,placeholder=a0b1c2d3e4f5==,required,secret"`
}

func (s *DDNSServer) serverURI() string {
	if strings.Contains(s.Server, ":") {
		return s.Server
	} else {
		return s.Server + ":53"
	}
}

func (s *DDNSServer) base64KeyBlob() string {
	return base64.StdEncoding.EncodeToString(s.KeyBlob)
}

func (s *DDNSServer) Validate() error {
	d := net.Dialer{}
	con, err := d.Dial("tcp", s.serverURI())
	if err != nil {
		return err
	}
	defer con.Close()

	s.KeyName = dns.Fqdn(s.KeyName)

	return nil
}

func (s *DDNSServer) DomainExists(fqdn string) error {
	d := net.Dialer{}
	con, err := d.Dial("tcp", s.serverURI())
	if err != nil {
		return err
	}
	defer con.Close()

	m := new(dns.Msg)
	m.SetEdns0(4096, true)
	m.SetQuestion(fqdn, dns.TypeSOA)

	c := new(dns.Client)
	c.TsigSecret = map[string]string{s.KeyName: s.base64KeyBlob()}
	m.SetTsig(s.KeyName, s.KeyAlgo, 300, time.Now().Unix())

	r, _, err := c.Exchange(m, s.serverURI())
	if err != nil {
		return err
	}

	// Check that the response is OK
	if r == nil {
		return fmt.Errorf("Response is nil")
	}
	if r.Rcode != dns.RcodeSuccess {
		return fmt.Errorf("Failed to get a valid answer from name server. Check that the domain %q lives on this server.", fqdn)
	}

	return nil
}

func (s *DDNSServer) ImportZone(dn *happydns.Domain) (rrs []dns.RR, err error) {
	d := net.Dialer{}
	con, errr := d.Dial("tcp", s.serverURI())
	if errr != nil {
		err = errr
		return
	}
	defer con.Close()

	m := new(dns.Msg)
	m.SetEdns0(4096, true)
	m.SetAxfr(dn.DomainName)
	m.SetTsig(s.KeyName, s.KeyAlgo, 300, time.Now().Unix())

	dnscon := &dns.Conn{Conn: con}
	transfer := &dns.Transfer{Conn: dnscon, TsigSecret: map[string]string{s.KeyName: s.base64KeyBlob()}}
	c, errr := transfer.In(m, s.serverURI())

	if errr != nil {
		err = errr
		return
	}

	for {
		response, ok := <-c
		if !ok {
			break
		}

		for _, rr := range response.RR {
			rrs = append(rrs, rr)
		}
	}

	if len(rrs) > 0 {
		rrs = rrs[0 : len(rrs)-1]
	}

	return
}

func (s *DDNSServer) AddRR(domain *happydns.Domain, rr dns.RR) error {
	m := new(dns.Msg)
	m.Id = dns.Id()
	m.Opcode = dns.OpcodeUpdate
	m.Question = make([]dns.Question, 1)
	m.Question[0] = dns.Question{domain.DomainName, dns.TypeSOA, dns.ClassINET}

	m.Insert([]dns.RR{rr})

	c := new(dns.Client)
	c.TsigSecret = map[string]string{s.KeyName: s.base64KeyBlob()}
	m.SetTsig(s.KeyName, s.KeyAlgo, 300, time.Now().Unix())

	_, _, err := c.Exchange(m, s.serverURI())
	return err
}

func (s *DDNSServer) DeleteRR(domain *happydns.Domain, rr dns.RR) error {
	m := new(dns.Msg)
	m.Id = dns.Id()
	m.Opcode = dns.OpcodeUpdate
	m.Question = make([]dns.Question, 1)
	m.Question[0] = dns.Question{domain.DomainName, dns.TypeSOA, dns.ClassINET}

	m.Remove([]dns.RR{rr})

	c := new(dns.Client)
	c.TsigSecret = map[string]string{s.KeyName: s.base64KeyBlob()}
	m.SetTsig(s.KeyName, s.KeyAlgo, 300, time.Now().Unix())

	_, _, err := c.Exchange(m, s.serverURI())
	return err
}

func (s *DDNSServer) UpdateSOA(domain *happydns.Domain, newSOA *dns.SOA, refreshSerial bool) (err error) {
	if refreshSerial {
		now := time.Now()
		todaySerial := uint32(now.Year()*1000000 + int(now.Month())*10000 + now.Day()*100)
		if newSOA.Serial >= todaySerial {
			newSOA.Serial += 1
		} else {
			newSOA.Serial = todaySerial
		}
	}

	return s.AddRR(domain, newSOA)
}

func init() {
	sources.RegisterSource(func() happydns.Source {
		return &DDNSServer{}
	}, sources.SourceInfos{
		Name:        "Dynamic DNS",
		Description: "If your zone is hosted on an authoritative name server that support Dynamic DNS (RFC 2136), such as Bind, Knot, ...",
	})
}