/*
 * Copyright (C) 2024 Jonni Liljamo <jonni@liljamo.com>
 *
 * This file is licensed under AGPL-3.0-or-later, see NOTICE and LICENSE for
 * more information.
 */

package dns

import (
	"log/slog"
	"net"
	"strings"

	"git.src.quest/~liljamo/felu/internal/config"
	"git.src.quest/~liljamo/felu/internal/db"
	"github.com/miekg/dns"
)

func parseQuery(m *dns.Msg, r *dns.Msg) {
	for _, q := range m.Question {
		slog.Info("Got Query",
			slog.Any("id", r.Id),
			slog.String("type", dns.TypeToString[q.Qtype]),
			slog.String("qname", q.Name),
		)

		switch q.Qtype {
		case dns.TypeA:
			handleARecord(&q, m, r)
		case dns.TypeAAAA:
			// NOTE: Stub
			m.SetRcode(r, dns.RcodeNameError)
		case dns.TypeCNAME:
			// NOTE: This is stubbed like this to make things like lego not shit themselves if they get NOTIMP.
			m.SetRcode(r, dns.RcodeNameError)
		case dns.TypeNS:
			handleNSRecord(&q, m, r)
		case dns.TypeSOA:
			handleSOARecord(&q, m, r)
		case dns.TypeTXT:
			handleTXTRecord(&q, m, r)
		default:
			m.SetRcode(r, dns.RcodeNotImplemented)
		}

		slog.Info("Responding to Query",
			slog.Any("id", r.Id),
			slog.String("rcode", dns.RcodeToString[m.Rcode]),
		)
	}
}

func handleARecord(q *dns.Question, m *dns.Msg, r *dns.Msg) {
	qName := strings.ToLower(q.Name)

	// TODO: This is probably not a great way to handle this, but it is what it is. For now.
	// "Root" Domain A.
	if qName == config.FeluConfig.Domain {
		m.Answer = append(m.Answer, &dns.A{
			Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 60},
			A:   net.ParseIP(config.FeluConfig.IPv4),
		})
		return
	}

	if index := strings.IndexByte(qName, '.'); index >= 0 {
		aRecord, err := db.FetchDomainARecord(qName[:index])
		if err != nil {
			m.SetRcode(r, dns.RcodeNameError)
		} else {
			m.Answer = append(m.Answer, &dns.A{
				Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 60},
				A:   net.ParseIP(aRecord),
			})
		}
	} else {
		m.SetRcode(r, dns.RcodeNameError)
	}
}

func handleNSRecord(q *dns.Question, m *dns.Msg, r *dns.Msg) {
	qName := strings.ToLower(q.Name)

	ns := &dns.NS{
		Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeNS, Class: dns.ClassINET, Ttl: 86400},
		Ns:  config.FeluConfig.Domain,
	}

	// "Root" Domain NS.
	if qName == config.FeluConfig.Domain {
		m.Answer = append(m.Answer, ns)
		return
	}

	if index := strings.IndexByte(qName, '.'); index >= 0 {
		// FIXME: other way of checking that the domain exists
		_, err := db.FetchDomainARecord(qName[:index])
		if err != nil {
			m.SetRcode(r, dns.RcodeNameError)
		} else {
			m.Answer = append(m.Answer, ns)
		}
	} else {
		m.SetRcode(r, dns.RcodeNameError)
	}
}

func handleSOARecord(q *dns.Question, m *dns.Msg, r *dns.Msg) {
	qName := strings.ToLower(q.Name)

	soa := &dns.SOA{
		Hdr:     dns.RR_Header{Name: q.Name, Rrtype: dns.TypeSOA, Class: dns.ClassINET, Ttl: 0},
		Ns:      config.FeluConfig.Domain,
		Mbox:    config.FeluConfig.SOAEmail,
		Serial:  2024100301,
		Refresh: 86400,
		Retry:   7200,
		Expire:  3600000,
		Minttl:  172800,
	}

	// "Root" Domain SOA.
	if qName == config.FeluConfig.Domain {
		m.Answer = append(m.Answer, soa)
		return
	}

	if index := strings.IndexByte(qName, '.'); index >= 0 {
		// FIXME: other way of checking that the domain exists
		_, err := db.FetchDomainARecord(qName[:index])
		if err != nil {
			m.SetRcode(r, dns.RcodeNameError)
		} else {
			m.Answer = append(m.Answer, soa)
		}
	} else {
		m.SetRcode(r, dns.RcodeNameError)
	}
}

func handleTXTRecord(q *dns.Question, m *dns.Msg, r *dns.Msg) {
	qName := strings.ToLower(q.Name)

	// NOTE: This handles only _acme-challenge queries
	expectedPrefix := "_acme-challenge."
	if !strings.HasPrefix(qName, expectedPrefix) {
		m.SetRcode(r, dns.RcodeNameError)
		return
	}

	qNameWithoutPrefix, ok := strings.CutPrefix(qName, expectedPrefix)
	if !ok {
		m.SetRcode(r, dns.RcodeFormatError)
		return
	}

	var ddnsDomain string
	if index := strings.IndexByte(qNameWithoutPrefix, '.'); index >= 0 {
		ddnsDomain = qNameWithoutPrefix[:index]
	} else {
		m.SetRcode(r, dns.RcodeNameError)
		return
	}

	txtRecord, err := db.FetchDomainAcmeChallenge(ddnsDomain)
	if err != nil {
		m.SetRcode(r, dns.RcodeNameError)
	} else {
		m.Answer = append(m.Answer, &dns.TXT{
			Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: 0},
			Txt: []string{txtRecord},
		})
	}
}