package resolver_test

import (
	"math/rand/v2"
	"slices"
	"testing"

	"github.com/miekg/dns"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"

	"sneak.berlin/go/dnswatcher/internal/resolver"
)

// TestCollectIPs_OneAnswerIsEnough checks that one nameserver answering
// NXDOMAIN says the name has no addresses, though the other timed out.
func TestCollectIPs_OneAnswerIsEnough(t *testing.T) {
	t.Parallel()

	ips, _, err := resolver.CollectIPs(
		map[string]*resolver.NameserverResponse{
			"ns1.example.": {Status: resolver.StatusTimeout},
			"ns2.example.": {Status: resolver.StatusNXDomain},
		},
	)
	require.NoError(t, err)
	assert.Empty(t, ips)
}

// TestCollectIPs_FailedIsNoAnswer checks that nameservers that all have
// status error, from a refusal, a server failure, a network error or a
// referral, are no answer rather than a name with no addresses.
func TestCollectIPs_FailedIsNoAnswer(t *testing.T) {
	t.Parallel()

	ips, _, err := resolver.CollectIPs(
		map[string]*resolver.NameserverResponse{
			"ns1.example.": {Status: resolver.StatusError},
			"ns2.example.": {Status: resolver.StatusError},
		},
	)
	require.ErrorIs(t, err, resolver.ErrNoNameserverAnswered)
	assert.Empty(t, ips)
}

const (
	// exampleCom is the zone most cases of TestUsableReply and
	// TestNSSetFrom are about, and wwwExampleCom a name in it.
	exampleCom    = "example.com."
	wwwExampleCom = "www.example.com."

	// exampleNS is the server the NS records nsRecord builds name.
	exampleNS = "ns1.example.net."
)

// nsRecord builds an NS record that names a server of zone.
func nsRecord(zone string) *dns.NS {
	return &dns.NS{
		Hdr: dns.RR_Header{
			Name: zone, Rrtype: dns.TypeNS, Class: dns.ClassINET,
		},
		Ns: exampleNS,
	}
}

// referralTo builds a reply that refers the query to the servers of
// zone.
func referralTo(zone string) *dns.Msg {
	msg := new(dns.Msg)
	msg.Ns = []dns.RR{nsRecord(zone)}

	return msg
}

// TestUsableReply checks which replies from one of a zone's servers are
// used. A reply that is not usable moves the query on to the zone's
// next server.
func TestUsableReply(t *testing.T) {
	t.Parallel()

	servfail := new(dns.Msg)
	servfail.Rcode = dns.RcodeServerFailure

	answer := new(dns.Msg)
	answer.Authoritative = true
	answer.Answer = []dns.RR{nsRecord(exampleCom)}

	nxdomain := new(dns.Msg)
	nxdomain.Authoritative = true
	nxdomain.Rcode = dns.RcodeNameError

	tests := []struct {
		name  string
		resp  *dns.Msg
		zone  string
		query string
		want  bool
	}{
		{
			name: "SERVFAIL", resp: servfail,
			zone: exampleCom, query: exampleCom, want: false,
		},
		{
			name: "answer", resp: answer,
			zone: exampleCom, query: exampleCom, want: true,
		},
		{
			name: "NXDOMAIN", resp: nxdomain,
			zone: ".", query: exampleCom, want: true,
		},
		{
			name: "root refers to com", resp: referralTo("com."),
			zone: ".", query: exampleCom, want: true,
		},
		{
			name: "com refers to example.com", resp: referralTo(exampleCom),
			zone: "com.", query: wwwExampleCom, want: true,
		},
		{
			name: "referral back to the zone", resp: referralTo(exampleCom),
			zone: exampleCom, query: exampleCom, want: false,
		},
		{
			name: "referral up to the root", resp: referralTo("."),
			zone: exampleCom, query: exampleCom, want: false,
		},
		{
			name: "referral sideways", resp: referralTo("net."),
			zone: ".", query: exampleCom, want: false,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			assert.Equal(t, tt.want,
				resolver.UsableReply(tt.resp, tt.zone, tt.query),
			)
		})
	}
}

// TestNSSetFrom checks which NS set a reply gives for a domain; a set
// that is not empty ends the walk. The referral to example.com that
// com's servers all send alike gives its delegation, so the set is the
// same whichever of them answered, and example.com's own servers, which
// can disagree, are not asked.
func TestNSSetFrom(t *testing.T) {
	t.Parallel()

	answer := new(dns.Msg)
	answer.Authoritative = true
	answer.Answer = []dns.RR{nsRecord(exampleCom)}

	tests := []struct {
		name   string
		resp   *dns.Msg
		domain string
		want   []string
	}{
		{
			name: "com refers to example.com", resp: referralTo(exampleCom),
			domain: exampleCom, want: []string{exampleNS},
		},
		{
			name: "com refers on, for www.example.com",
			resp: referralTo(exampleCom), domain: wwwExampleCom,
			want: nil,
		},
		{
			name: "answer from a server that holds example.com",
			resp: answer, domain: exampleCom,
			want: []string{exampleNS},
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			assert.ElementsMatch(t, tt.want,
				resolver.NSSetFrom(tt.resp, tt.domain),
			)
		})
	}
}

func TestExtractRecordValue_LetterCase(t *testing.T) {
	t.Parallel()

	tests := []struct {
		name string
		rr   dns.RR
		want string
	}{
		{
			name: "MX target lower-cased",
			rr:   &dns.MX{Preference: 1, Mx: "ASPMX.L.GOOGLE.COM."},
			want: "1 aspmx.l.google.com.",
		},
		{
			name: "NS target lower-cased",
			rr:   &dns.NS{Ns: "x.ns.joker.COM."},
			want: "x.ns.joker.com.",
		},
		{
			name: "CNAME target lower-cased",
			rr:   &dns.CNAME{Target: "WWW.Example.Com."},
			want: "www.example.com.",
		},
		{
			name: "SRV target lower-cased",
			rr: &dns.SRV{
				Priority: 10, Weight: 5, Port: 443,
				Target: "SIP.Example.Com.",
			},
			want: "10 5 443 sip.example.com.",
		},
		{
			name: "TXT value keeps its case",
			rr:   &dns.TXT{Txt: []string{"Verify=AbC123"}},
			want: "Verify=AbC123",
		},
		{
			name: "CAA value keeps its case",
			rr:   &dns.CAA{Flag: 0, Tag: "issue", Value: "LetsEncrypt.org"},
			want: `0 issue "LetsEncrypt.org"`,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			assert.Equal(t, tt.want, resolver.ExtractRecordValue(tt.rr))
		})
	}
}

// TestCollectAnswerRecords_CNAMEOnce collects the answers a nameserver
// gives for a name with a CNAME, one for each record type a check asks
// for. Each answer holds the CNAME, which must be stored once.
func TestCollectAnswerRecords_CNAMEOnce(t *testing.T) {
	t.Parallel()

	cname := &dns.CNAME{
		Hdr: dns.RR_Header{
			Name: "git.eeqj.de.", Rrtype: dns.TypeCNAME, Class: dns.ClassINET,
		},
		Target: "fsn1app1.datavi.be.",
	}

	resp := &resolver.NameserverResponse{Records: map[string][]string{}}

	for _, qtype := range []uint16{
		dns.TypeA, dns.TypeAAAA, dns.TypeCNAME, dns.TypeMX,
		dns.TypeTXT, dns.TypeSRV, dns.TypeCAA, dns.TypeNS,
	} {
		msg := new(dns.Msg)
		msg.SetQuestion("git.eeqj.de.", qtype)
		msg.Answer = []dns.RR{cname}

		resolver.CollectAnswerRecords(msg, resp)
	}

	assert.Equal(t,
		map[string][]string{"CNAME": {"fsn1app1.datavi.be."}},
		resp.Records,
	)
}

// TestShuffled shuffles the root servers with many seeds. Every order
// must hold each root server once, so each is tried before a
// resolution fails; each root server must come first for some seed, so
// no one root server gets every first query; and the list passed in
// must be left as it was.
func TestShuffled(t *testing.T) {
	t.Parallel()

	const seeds = 1000

	roots := resolver.RootServerList()
	before := slices.Clone(roots)
	first := make(map[string]bool)

	for seed := range uint64(seeds) {
		rng := rand.New(rand.NewPCG(seed, 0)) //nolint:gosec // seeded on purpose
		order := resolver.Shuffled(roots, rng.Shuffle)

		assert.ElementsMatch(t, roots, order)

		first[order[0]] = true
	}

	assert.Len(t, first, len(roots))
	assert.Equal(t, before, roots)
}