package resolver_test

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

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

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

// Test domain and hostnames hosted on Cloudflare.
// These records must exist in the sneak.cloud Cloudflare zone:
//
//	basic.dns.sneak.cloud    A      192.0.2.1
//	multi.dns.sneak.cloud    A      192.0.2.1
//	multi.dns.sneak.cloud    A      192.0.2.2
//	ipv6.dns.sneak.cloud     AAAA   2001:db8::1
//	dual.dns.sneak.cloud     A      192.0.2.1
//	dual.dns.sneak.cloud     AAAA   2001:db8::1
//	cname-target.dns.sneak.cloud  A      198.51.100.1
//	cname.dns.sneak.cloud    CNAME  cname-target.dns.sneak.cloud
//	mx.dns.sneak.cloud       MX     10 mail.dns.sneak.cloud
//	mail.dns                 A      192.0.2.10
//	txt.dns.sneak.cloud      TXT    "v=spf1 -all"
const (
	testDomain          = "sneak.cloud"
	testHostBasic       = "basic.dns.sneak.cloud"
	testHostMultiA      = "multi.dns.sneak.cloud"
	testHostIPv6        = "ipv6.dns.sneak.cloud"
	testHostDualStack   = "dual.dns.sneak.cloud"
	testHostCNAME       = "cname.dns.sneak.cloud"
	testHostCNAMETarget = "cname-target.dns.sneak.cloud"
	testHostMX          = "mx.dns.sneak.cloud"
	testHostMail        = "mail.dns.sneak.cloud"
	testHostTXT         = "txt.dns.sneak.cloud"
	testHostNXDomain    = "nxdomain-surely-does-not-exist.google.com"
	testDomainNXDomain  = "google.com"
)

// queryTimeout is the default timeout for test queries.
const queryTimeout = 60 * time.Second

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)
}

func testContext(t *testing.T) context.Context {
	t.Helper()

	ctx, cancel := context.WithTimeout(
		context.Background(), queryTimeout,
	)
	t.Cleanup(cancel)

	return ctx
}

// --- FindAuthoritativeNameservers tests ---

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

	r := newTestResolver(t)
	ctx := testContext(t)

	nameservers, err := r.FindAuthoritativeNameservers(
		ctx, testDomain,
	)
	require.NoError(t, err)
	require.NotEmpty(t, nameservers, "should find at least one NS")

	// sneak.cloud is on Cloudflare, NS should contain cloudflare
	for _, ns := range nameservers {
		t.Logf("discovered NS: %s", ns)
		assert.True(
			t,
			strings.HasSuffix(ns, "."),
			"NS should be FQDN with trailing dot: %s", ns,
		)
	}

	// Verify at least one is a Cloudflare NS
	hasCloudflare := false

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

			break
		}
	}

	assert.True(
		t, hasCloudflare,
		"sneak.cloud should be hosted on Cloudflare, got: %v",
		nameservers,
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	// Looking up NS for a hostname that isn't a zone should
	// return the parent zone's NS records.
	nameservers, err := r.FindAuthoritativeNameservers(
		ctx, testHostBasic,
	)
	require.NoError(t, err)
	require.NotEmpty(t, nameservers)

	// Should be the same Cloudflare NSes as the parent domain
	hasCloudflare := false

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

			break
		}
	}

	assert.True(t, hasCloudflare)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	nameservers, err := r.FindAuthoritativeNameservers(
		ctx, "cloud",
	)
	require.NoError(t, err)
	require.NotEmpty(t, nameservers, "should find TLD nameservers")

	for _, ns := range nameservers {
		t.Logf("TLD NS: %s", ns)
	}
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	nameservers, err := r.FindAuthoritativeNameservers(
		ctx, testDomain,
	)
	require.NoError(t, err)
	require.NotEmpty(t, nameservers)

	// Results should be sorted for deterministic comparison
	assert.True(
		t,
		sort.StringsAreSorted(nameservers),
		"nameservers should be sorted, got: %v", nameservers,
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	first, err := r.FindAuthoritativeNameservers(
		ctx, testDomain,
	)
	require.NoError(t, err)

	second, err := r.FindAuthoritativeNameservers(
		ctx, testDomain,
	)
	require.NoError(t, err)

	assert.Equal(
		t, first, second,
		"repeated lookups should return same result",
	)
}

// --- QueryNameserver tests ---

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	resp, err := r.QueryNameserver(ctx, ns, testHostBasic)
	require.NoError(t, err)
	require.NotNil(t, resp)

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

	aRecords := resp.Records["A"]
	require.NotEmpty(t, aRecords, "basic.dns should have A records")
	assert.Contains(t, aRecords, "192.0.2.1")

	t.Logf(
		"QueryNameserver(%s, %s) A records: %v",
		ns, testHostBasic, aRecords,
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	resp, err := r.QueryNameserver(ctx, ns, testHostMultiA)
	require.NoError(t, err)
	require.NotNil(t, resp)
	assert.Equal(t, resolver.StatusOK, resp.Status)

	aRecords := resp.Records["A"]
	require.Len(
		t, aRecords, 2,
		"multi.dns should have exactly 2 A records",
	)

	sort.Strings(aRecords)
	assert.Equal(t, []string{"192.0.2.1", "192.0.2.2"}, aRecords)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	resp, err := r.QueryNameserver(ctx, ns, testHostIPv6)
	require.NoError(t, err)
	require.NotNil(t, resp)
	assert.Equal(t, resolver.StatusOK, resp.Status)

	aaaaRecords := resp.Records["AAAA"]
	require.NotEmpty(
		t, aaaaRecords,
		"ipv6.dns should have AAAA records",
	)
	assert.Contains(t, aaaaRecords, "2001:db8::1")
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	resp, err := r.QueryNameserver(ctx, ns, testHostDualStack)
	require.NoError(t, err)
	require.NotNil(t, resp)
	assert.Equal(t, resolver.StatusOK, resp.Status)

	assert.Contains(t, resp.Records["A"], "192.0.2.1")
	assert.Contains(t, resp.Records["AAAA"], "2001:db8::1")
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	resp, err := r.QueryNameserver(ctx, ns, testHostCNAME)
	require.NoError(t, err)
	require.NotNil(t, resp)
	assert.Equal(t, resolver.StatusOK, resp.Status)

	cnameRecords := resp.Records["CNAME"]
	require.NotEmpty(
		t, cnameRecords,
		"cname.dns should have CNAME records",
	)
	assert.Contains(
		t, cnameRecords, "cname-target.dns.sneak.cloud.",
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	resp, err := r.QueryNameserver(ctx, ns, testHostMX)
	require.NoError(t, err)
	require.NotNil(t, resp)
	assert.Equal(t, resolver.StatusOK, resp.Status)

	mxRecords := resp.Records["MX"]
	require.NotEmpty(
		t, mxRecords,
		"mx.dns should have MX records",
	)

	// MX records are formatted as "priority host"
	hasMail := false

	for _, mx := range mxRecords {
		if strings.Contains(mx, "mail.dns.sneak.cloud.") {
			hasMail = true

			break
		}
	}

	assert.True(
		t, hasMail,
		"MX should reference mail.dns.sneak.cloud, got: %v",
		mxRecords,
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	resp, err := r.QueryNameserver(ctx, ns, testHostTXT)
	require.NoError(t, err)
	require.NotNil(t, resp)
	assert.Equal(t, resolver.StatusOK, resp.Status)

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

	hasSPF := false

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

			break
		}
	}

	assert.True(
		t, hasSPF,
		"TXT should contain SPF record, got: %v", txtRecords,
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNSForDomain(t, r, ctx, testDomainNXDomain)

	resp, err := r.QueryNameserver(ctx, ns, testHostNXDomain)
	require.NoError(t, err)
	require.NotNil(t, resp)

	assert.Equal(
		t, resolver.StatusNXDomain, resp.Status,
		"nonexistent host should return nxdomain status",
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	resp, err := r.QueryNameserver(ctx, ns, testHostMultiA)
	require.NoError(t, err)

	// Each record type's values should be sorted for determinism
	for recordType, values := range resp.Records {
		assert.True(
			t,
			sort.StringsAreSorted(values),
			"%s records should be sorted, got: %v",
			recordType, values,
		)
	}
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	resp, err := r.QueryNameserver(ctx, ns, testHostBasic)
	require.NoError(t, err)

	assert.Equal(
		t, ns, resp.Nameserver,
		"response should include the queried nameserver",
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNSForDomain(t, r, ctx, testDomainNXDomain)

	resp, err := r.QueryNameserver(ctx, ns, testHostNXDomain)
	require.NoError(t, err)

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

	assert.Zero(
		t, totalRecords,
		"NXDOMAIN should have no records, got: %v",
		resp.Records,
	)
}

// --- QueryAllNameservers tests ---

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

	r := newTestResolver(t)
	ctx := testContext(t)

	results, err := r.QueryAllNameservers(ctx, testHostBasic)
	require.NoError(t, err)
	require.NotEmpty(t, results)

	// Should have queried each NS independently
	t.Logf(
		"QueryAllNameservers returned %d nameserver results",
		len(results),
	)

	for ns, resp := range results {
		t.Logf("  %s: status=%s A=%v", ns, resp.Status, resp.Records["A"])
		assert.Equal(t, ns, resp.Nameserver)
	}

	// Should have more than one NS for Cloudflare-hosted domain
	assert.GreaterOrEqual(
		t, len(results), 2,
		"should query at least 2 nameservers",
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	results, err := r.QueryAllNameservers(ctx, testHostBasic)
	require.NoError(t, err)
	require.NotEmpty(t, results)

	// All NSes should return the same A records for a
	// well-configured hostname.
	var referenceRecords map[string][]string

	for ns, resp := range results {
		require.Equal(
			t, resolver.StatusOK, resp.Status,
			"NS %s should return OK status", ns,
		)

		if referenceRecords == nil {
			referenceRecords = resp.Records

			continue
		}

		assert.Equal(
			t, referenceRecords["A"], resp.Records["A"],
			"NS %s A records should match", ns,
		)
	}
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	results, err := r.QueryAllNameservers(
		ctx, testHostNXDomain,
	)
	require.NoError(t, err)
	require.NotEmpty(t, results)

	for ns, resp := range results {
		assert.Equal(
			t, resolver.StatusNXDomain, resp.Status,
			"NS %s should return nxdomain for nonexistent host",
			ns,
		)
	}
}

// --- LookupNS tests ---

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

	r := newTestResolver(t)
	ctx := testContext(t)

	nameservers, err := r.LookupNS(ctx, testDomain)
	require.NoError(t, err)
	require.NotEmpty(t, nameservers)

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

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

	r := newTestResolver(t)
	ctx := testContext(t)

	nameservers, err := r.LookupNS(ctx, testDomain)
	require.NoError(t, err)

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

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

	r := newTestResolver(t)
	ctx := testContext(t)

	fromLookup, err := r.LookupNS(ctx, testDomain)
	require.NoError(t, err)

	fromFind, err := r.FindAuthoritativeNameservers(
		ctx, testDomain,
	)
	require.NoError(t, err)

	// Both methods should return the same NS set
	assert.Equal(
		t, fromFind, fromLookup,
		"LookupNS and FindAuthoritativeNameservers "+
			"should return the same set",
	)
}

// --- ResolveIPAddresses tests ---

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ips, err := r.ResolveIPAddresses(ctx, testHostBasic)
	require.NoError(t, err)
	require.NotEmpty(t, ips)
	assert.Contains(t, ips, "192.0.2.1")
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ips, err := r.ResolveIPAddresses(ctx, testHostMultiA)
	require.NoError(t, err)

	sort.Strings(ips)
	assert.Contains(t, ips, "192.0.2.1")
	assert.Contains(t, ips, "192.0.2.2")
}

func TestResolveIPAddresses_IPv6Only(t *testing.T) {
	t.Parallel()

	r := newTestResolver(t)
	ctx := testContext(t)

	ips, err := r.ResolveIPAddresses(ctx, testHostIPv6)
	require.NoError(t, err)
	require.NotEmpty(t, ips)
	assert.Contains(t, ips, "2001:db8::1")

	// Should not contain any IPv4
	for _, ip := range ips {
		parsed := net.ParseIP(ip)
		require.NotNil(t, parsed, "should be valid IP: %s", ip)
		assert.Nil(
			t, parsed.To4(),
			"ipv6-only host should not return IPv4: %s", ip,
		)
	}
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ips, err := r.ResolveIPAddresses(ctx, testHostDualStack)
	require.NoError(t, err)

	assert.Contains(t, ips, "192.0.2.1")
	assert.Contains(t, ips, "2001:db8::1")
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	// cname.dns.sneak.cloud -> cname-target.dns.sneak.cloud -> 198.51.100.1
	ips, err := r.ResolveIPAddresses(ctx, testHostCNAME)
	require.NoError(t, err)
	require.NotEmpty(t, ips)
	assert.Contains(
		t, ips, "198.51.100.1",
		"should follow CNAME to resolve target IP",
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ips, err := r.ResolveIPAddresses(ctx, testHostBasic)
	require.NoError(t, err)

	// Check for duplicates
	seen := make(map[string]bool)

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

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ips, err := r.ResolveIPAddresses(ctx, testHostDualStack)
	require.NoError(t, err)

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

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ips, err := r.ResolveIPAddresses(ctx, testHostNXDomain)
	// Should not error — NXDOMAIN is an expected DNS response.
	// It just means no IPs to return.
	require.NoError(t, err)
	assert.Empty(t, ips)
}

// --- Context cancellation tests ---

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

	r := newTestResolver(t)

	ctx, cancel := context.WithCancel(context.Background())
	cancel() // Cancel immediately

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

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

	r := newTestResolver(t)

	ctx, cancel := context.WithCancel(context.Background())
	cancel()

	_, err := r.ResolveIPAddresses(ctx, testHostBasic)
	assert.Error(t, err)
}

// --- Iterative resolution verification ---

func TestFindAuthoritativeNameservers_IsIterative(
	t *testing.T,
) {
	// Verify that resolution works for well-known domains,
	// proving we trace from root rather than relying on a
	// system stub resolver that might not be configured.
	t.Parallel()

	r := newTestResolver(t)
	ctx := testContext(t)

	// Resolve a well-known domain to prove root->TLD->domain
	// tracing works.
	nameservers, err := r.FindAuthoritativeNameservers(
		ctx, "google.com",
	)
	require.NoError(t, err)
	require.NotEmpty(t, nameservers)

	t.Logf("example.com NS: %v", nameservers)
}

// --- Edge cases ---

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns := findOneNS(t, r, ctx)

	// Both with and without trailing dot should work
	resp1, err := r.QueryNameserver(
		ctx, ns, "basic.dns.sneak.cloud",
	)
	require.NoError(t, err)

	resp2, err := r.QueryNameserver(
		ctx, ns, "basic.dns.sneak.cloud.",
	)
	require.NoError(t, err)

	assert.Equal(
		t, resp1.Records["A"], resp2.Records["A"],
		"trailing dot should not affect results",
	)
}

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

	r := newTestResolver(t)
	ctx := testContext(t)

	ns1, err := r.FindAuthoritativeNameservers(
		ctx, "sneak.cloud",
	)
	require.NoError(t, err)

	ns2, err := r.FindAuthoritativeNameservers(
		ctx, "sneak.cloud.",
	)
	require.NoError(t, err)

	assert.Equal(
		t, ns1, ns2,
		"trailing dot should not affect NS lookup",
	)
}

// --- Helper functions ---

// findOneNS discovers authoritative nameservers and returns the first
// one, failing the test if none are found.
func findOneNS(
	t *testing.T,
	r *resolver.Resolver,
	ctx context.Context, //nolint:revive // test helper
) string {
	t.Helper()

	return findOneNSForDomain(t, r, ctx, testDomain)
}

func findOneNSForDomain(
	t *testing.T,
	r *resolver.Resolver,
	ctx context.Context, //nolint:revive // test helper
	domain string,
) string {
	t.Helper()

	nameservers, err := r.FindAuthoritativeNameservers(
		ctx, domain,
	)
	require.NoError(t, err)
	require.NotEmpty(
		t, nameservers,
		"should find at least one NS for %s", domain,
	)

	return nameservers[0]
}