/*
 * Copyright (C) 2020-2022, IrineSistiana
 *
 * This file is part of mosdns.
 *
 * mosdns is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * mosdns is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package dnsutils

import (
	"github.com/miekg/dns"
	"strconv"
)

// GetMinimalTTL returns the minimal ttl of this msg.
// If msg m has no record, it returns 0.
func GetMinimalTTL(m *dns.Msg) uint32 {
	minTTL := ^uint32(0)
	hasRecord := false
	for _, section := range [...][]dns.RR{m.Answer, m.Ns, m.Extra} {
		for _, rr := range section {
			hdr := rr.Header()
			if hdr.Rrtype == dns.TypeOPT {
				continue // opt record ttl is not ttl.
			}
			hasRecord = true
			ttl := hdr.Ttl
			if ttl < minTTL {
				minTTL = ttl
			}
		}
	}

	if !hasRecord { // no ttl applied
		return 0
	}
	return minTTL
}

// SetTTL updates all records' ttl to ttl, except opt record.
func SetTTL(m *dns.Msg, ttl uint32) {
	for _, section := range [...][]dns.RR{m.Answer, m.Ns, m.Extra} {
		for _, rr := range section {
			hdr := rr.Header()
			if hdr.Rrtype == dns.TypeOPT {
				continue // opt record ttl is not ttl.
			}
			hdr.Ttl = ttl
		}
	}
}

func ApplyMaximumTTL(m *dns.Msg, ttl uint32) {
	applyTTL(m, ttl, true)
}

func ApplyMinimalTTL(m *dns.Msg, ttl uint32) {
	applyTTL(m, ttl, false)
}

// SubtractTTL subtract delta from every m's RR.
// If RR's TTL is smaller than delta, SubtractTTL
// will return overflowed = true.
func SubtractTTL(m *dns.Msg, delta uint32) (overflowed bool) {
	for _, section := range [...][]dns.RR{m.Answer, m.Ns, m.Extra} {
		for _, rr := range section {
			hdr := rr.Header()
			if hdr.Rrtype == dns.TypeOPT {
				continue // opt record ttl is not ttl.
			}
			if ttl := hdr.Ttl; ttl > delta {
				hdr.Ttl = ttl - delta
			} else {
				hdr.Ttl = 1
				overflowed = true
			}
		}
	}
	return
}

func applyTTL(m *dns.Msg, ttl uint32, maximum bool) {
	for _, section := range [...][]dns.RR{m.Answer, m.Ns, m.Extra} {
		for _, rr := range section {
			hdr := rr.Header()
			if hdr.Rrtype == dns.TypeOPT {
				continue // opt record ttl is not ttl.
			}
			if maximum {
				if hdr.Ttl > ttl {
					hdr.Ttl = ttl
				}
			} else {
				if hdr.Ttl < ttl {
					hdr.Ttl = ttl
				}
			}
		}
	}
}

func uint16Conv(u uint16, m map[uint16]string) string {
	if s, ok := m[u]; ok {
		return s
	}
	return strconv.Itoa(int(u))
}

func QclassToString(u uint16) string {
	return uint16Conv(u, dns.ClassToString)
}

func QtypeToString(u uint16) string {
	return uint16Conv(u, dns.TypeToString)
}

func GenEmptyReply(q *dns.Msg, rcode int) *dns.Msg {
	r := new(dns.Msg)
	r.SetRcode(q, rcode)

	var name string
	if len(q.Question) > 1 {
		name = q.Question[0].Name
	} else {
		name = "."
	}

	r.Ns = []dns.RR{FakeSOA(name)}
	return r
}

func FakeSOA(name string) *dns.SOA {
	return &dns.SOA{
		Hdr: dns.RR_Header{
			Name:   name,
			Rrtype: dns.TypeSOA,
			Class:  dns.ClassINET,
			Ttl:    300,
		},
		Ns:      "fake-ns.mosdns.fake.root.",
		Mbox:    "fake-mbox.mosdns.fake.root.",
		Serial:  2021110400,
		Refresh: 1800,
		Retry:   900,
		Expire:  604800,
		Minttl:  86400,
	}
}