package resolver_test

import (
	"context"
	"log/slog"
	"net"
	"os"
	"sort"
	"strings"
	"testing"
	"time"

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

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

// ----------------------------------------------------------------
// Test helpers
// ----------------------------------------------------------------

func newTestResolver(t *testing.T) *resolver.Resolver {
	t.Helper()

	log := slog.New(slog.NewTextHandler(
		os.Stderr,
		&slog.HandlerOptions{Level: slog.LevelDebug},
	))

	return resolver.NewFromLogger(log)
}

// findOneNSForDomain picks one authoritative nameserver to aim a
// test at. Live-DNS retry, concurrency and quorum handling live in
// livedns_test.go.
func findOneNSForDomain(
	t *testing.T,
	r *resolver.Resolver,
	domain string,
) string {
	t.Helper()

	return liveFindAuthoritative(t, r, domain)[0]
}

// ----------------------------------------------------------------
// FindAuthoritativeNameservers tests
// ----------------------------------------------------------------

func TestFindAuthoritativeNameservers_ValidDomain(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	nameservers := liveFindAuthoritative(t, r, "google.com")

	hasGoogleNS := false

	for _, ns := range nameservers {
		if strings.Contains(ns, "google") {
			hasGoogleNS = true

			break
		}
	}

	assert.True(t, hasGoogleNS,
		"expected google nameservers, got: %v", nameservers,
	)
}

func TestFindAuthoritativeNameservers_Subdomain(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	nameservers := liveFindAuthoritative(t, r, "www.google.com")

	assert.NotEmpty(t, nameservers)
}

func TestFindAuthoritativeNameservers_ReturnsSorted(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	nameservers := liveFindAuthoritative(t, r, "google.com")

	assert.True(
		t,
		sort.StringsAreSorted(nameservers),
		"nameservers should be sorted, got: %v", nameservers,
	)
}

func TestFindAuthoritativeNameservers_Deterministic(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	first := liveFindAuthoritative(t, r, "google.com")
	second := liveFindAuthoritative(t, r, "google.com")

	assert.Equal(t, first, second)
}

func TestFindAuthoritativeNameservers_TrailingDot(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	ns1 := liveFindAuthoritative(t, r, "google.com")
	ns2 := liveFindAuthoritative(t, r, "google.com.")

	assert.Equal(t, ns1, ns2)
}

func TestFindAuthoritativeNameservers_CloudflareDomain(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	nameservers := liveFindAuthoritative(t, r, "cloudflare.com")

	for _, ns := range nameservers {
		assert.True(t, strings.HasSuffix(ns, "."),
			"NS should be FQDN with trailing dot: %s", ns,
		)
	}
}

// ----------------------------------------------------------------
// QueryNameserver tests
// ----------------------------------------------------------------

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

	r := newTestResolver(t)
	ns := findOneNSForDomain(t, r, "google.com")
	resp := liveQueryNameserver(t, r, ns, "www.google.com")

	require.NotNil(t, resp)

	assert.Equal(t, resolver.StatusOK, resp.Status)
	assert.Equal(t, ns, resp.Nameserver)

	hasRecords := len(resp.Records["A"]) > 0 ||
		len(resp.Records["CNAME"]) > 0
	assert.True(t, hasRecords,
		"expected A or CNAME records for www.google.com",
	)
}

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

	r := newTestResolver(t)
	ns := findOneNSForDomain(t, r, "cloudflare.com")
	resp := liveQueryNameserver(t, r, ns, "cloudflare.com")

	aaaaRecords := resp.Records["AAAA"]
	require.NotEmpty(t, aaaaRecords,
		"cloudflare.com should have AAAA records",
	)

	for _, ip := range aaaaRecords {
		parsed := net.ParseIP(ip)
		require.NotNil(t, parsed,
			"should be valid IP: %s", ip,
		)
	}
}

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

	r := newTestResolver(t)
	ns := findOneNSForDomain(t, r, "google.com")
	resp := liveQueryNameserver(t, r, ns, "google.com")

	mxRecords := resp.Records["MX"]
	require.NotEmpty(t, mxRecords,
		"google.com should have MX records",
	)
}

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

	r := newTestResolver(t)
	ns := findOneNSForDomain(t, r, "google.com")
	resp := liveQueryNameserver(t, r, ns, "google.com")

	txtRecords := resp.Records["TXT"]
	require.NotEmpty(t, txtRecords,
		"google.com should have TXT records",
	)

	hasSPF := false

	for _, txt := range txtRecords {
		if strings.Contains(txt, "v=spf1") {
			hasSPF = true

			break
		}
	}

	assert.True(t, hasSPF,
		"google.com should have SPF TXT record",
	)
}

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

	r := newTestResolver(t)
	ns := findOneNSForDomain(t, r, "google.com")
	resp := liveQueryNameserver(
		t, r, ns, "this-surely-does-not-exist-xyz.google.com",
	)

	assert.Equal(t, resolver.StatusNXDomain, resp.Status)
}

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

	r := newTestResolver(t)
	ns := findOneNSForDomain(t, r, "google.com")
	resp := liveQueryNameserver(t, r, ns, "google.com")

	for recordType, values := range resp.Records {
		assert.True(
			t,
			sort.StringsAreSorted(values),
			"%s records should be sorted", recordType,
		)
	}
}

func TestQueryNameserver_ResponseIncludesNameserver(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	ns := findOneNSForDomain(t, r, "cloudflare.com")
	resp := liveQueryNameserver(t, r, ns, "cloudflare.com")

	assert.Equal(t, ns, resp.Nameserver)
}

func TestQueryNameserver_EmptyRecordsOnNXDomain(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	ns := findOneNSForDomain(t, r, "google.com")
	resp := liveQueryNameserver(
		t, r, ns, "this-surely-does-not-exist-xyz.google.com",
	)

	totalRecords := 0
	for _, values := range resp.Records {
		totalRecords += len(values)
	}

	assert.Zero(t, totalRecords)
}

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

	r := newTestResolver(t)
	ns := findOneNSForDomain(t, r, "google.com")
	resp1 := liveQueryNameserver(t, r, ns, "google.com")
	resp2 := liveQueryNameserver(t, r, ns, "google.com.")

	assert.Equal(t, resp1.Status, resp2.Status)
}

// ----------------------------------------------------------------
// QueryAllNameservers tests
// ----------------------------------------------------------------

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

	r := newTestResolver(t)
	results := liveQueryAllNameservers(t, r, "google.com")

	assert.GreaterOrEqual(t, len(results), minNameservers)

	for ns, resp := range results {
		assert.Equal(t, ns, resp.Nameserver)
	}
}

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

	r := newTestResolver(t)
	results := liveQueryAllNameservers(t, r, "google.com")

	// A quorum, not unanimity: one authoritative server being
	// slow or rate-limiting us is a property of the live
	// internet, not a resolver defect.
	assert.GreaterOrEqual(
		t,
		countStatus(results, resolver.StatusOK),
		liveQuorum(len(results)),
		"a quorum of nameservers should answer OK: %s",
		describeStatuses(results),
	)

	// Any nameserver claiming google.com does not exist is a
	// real failure and is never tolerated.
	assert.Zero(
		t,
		countStatus(results, resolver.StatusNXDomain),
		"no nameserver should report NXDOMAIN: %s",
		describeStatuses(results),
	)
}

func TestQueryAllNameservers_NXDomainFromAllNS(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	results := liveQueryAllNameservers(
		t, r, "this-surely-does-not-exist-xyz.google.com",
	)

	assert.GreaterOrEqual(
		t,
		countStatus(results, resolver.StatusNXDomain),
		liveQuorum(len(results)),
		"a quorum of nameservers should report NXDOMAIN: %s",
		describeStatuses(results),
	)

	// Silence is tolerated; a positive answer for a name that
	// does not exist is not.
	assert.Zero(
		t,
		countStatus(results, resolver.StatusOK),
		"no nameserver should answer OK: %s",
		describeStatuses(results),
	)
}

// ----------------------------------------------------------------
// LookupNS tests
// ----------------------------------------------------------------

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

	r := newTestResolver(t)
	nameservers := liveLookupNS(t, r, "google.com")

	for _, ns := range nameservers {
		assert.True(t, strings.HasSuffix(ns, "."),
			"NS should have trailing dot: %s", ns,
		)
	}
}

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

	r := newTestResolver(t)
	nameservers := liveLookupNS(t, r, "google.com")

	assert.True(t, sort.StringsAreSorted(nameservers))
}

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

	r := newTestResolver(t)
	fromLookup := liveLookupNS(t, r, "google.com")
	fromFind := liveFindAuthoritative(t, r, "google.com")

	assert.Equal(t, fromFind, fromLookup)
}

// ----------------------------------------------------------------
// ResolveIPAddresses tests
// ----------------------------------------------------------------

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

	r := newTestResolver(t)
	ips := liveResolveIPs(t, r, "google.com")

	for _, ip := range ips {
		parsed := net.ParseIP(ip)
		assert.NotNil(t, parsed,
			"should be valid IP: %s", ip,
		)
	}
}

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

	r := newTestResolver(t)
	ips := liveResolveIPs(t, r, "google.com")

	seen := make(map[string]bool)

	for _, ip := range ips {
		assert.False(t, seen[ip], "duplicate IP: %s", ip)
		seen[ip] = true
	}
}

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

	r := newTestResolver(t)
	ips := liveResolveIPs(t, r, "google.com")

	assert.True(t, sort.StringsAreSorted(ips))
}

func TestResolveIPAddresses_NXDomainReturnsEmpty(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	ips := liveResolveIPsAllowingEmpty(
		t, r, "this-surely-does-not-exist-xyz.google.com",
	)

	assert.Empty(t, ips)
}

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

	r := newTestResolver(t)
	ips := liveResolveIPs(t, r, "cloudflare.com")

	assert.NotEmpty(t, ips)
}

// ----------------------------------------------------------------
// Context cancellation tests
// ----------------------------------------------------------------

func TestFindAuthoritativeNameservers_ContextCanceled(
	t *testing.T,
) {
	t.Parallel()

	r := newTestResolver(t)
	ctx, cancel := context.WithCancel(context.Background())
	cancel()

	_, err := r.FindAuthoritativeNameservers(ctx, "google.com")
	assert.Error(t, err)
}

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

	r := newTestResolver(t)
	ctx, cancel := context.WithCancel(context.Background())
	cancel()

	_, err := r.QueryNameserver(
		ctx, "ns1.google.com.", "google.com",
	)
	assert.Error(t, err)
}

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

	r := newTestResolver(t)
	ctx, cancel := context.WithCancel(context.Background())
	cancel()

	_, err := r.QueryAllNameservers(ctx, "google.com")
	assert.Error(t, err)
}

// ----------------------------------------------------------------
// Timeout tests
// ----------------------------------------------------------------

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

	log := slog.New(slog.NewTextHandler(
		os.Stderr,
		&slog.HandlerOptions{Level: slog.LevelDebug},
	))

	r := resolver.NewFromLoggerWithClient(
		log, &timeoutClient{},
	)

	ctx, cancel := context.WithTimeout(
		context.Background(), 10*time.Second,
	)
	t.Cleanup(cancel)

	// Query any IP — the client always returns a timeout error.
	resp, err := r.QueryNameserverIP(
		ctx, "unreachable.test.", "192.0.2.1",
		"example.com",
	)
	require.NoError(t, err)

	assert.Equal(t, resolver.StatusTimeout, resp.Status)
	assert.NotEmpty(t, resp.Error)
}

// timeoutClient simulates DNS timeout errors for testing.
type timeoutClient struct{}

func (c *timeoutClient) ExchangeContext(
	_ context.Context,
	_ *dns.Msg,
	_ string,
) (*dns.Msg, time.Duration, error) {
	return nil, 0, &net.OpError{
		Op:  "read",
		Net: "udp",
		Err: &timeoutError{},
	}
}

type timeoutError struct{}

func (e *timeoutError) Error() string   { return "i/o timeout" }
func (e *timeoutError) Timeout() bool   { return true }
func (e *timeoutError) Temporary() bool { return true }

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

	r := newTestResolver(t)
	ctx, cancel := context.WithCancel(context.Background())
	cancel()

	_, err := r.ResolveIPAddresses(ctx, "google.com")
	assert.Error(t, err)
}