package dns

import (
	"context"
	"errors"
	"net"
	"sync"
	"testing"

	"github.com/miekg/dns"
)

func TestIterativeQueryWithExchangeSuccess(t *testing.T) {
	resp := new(dns.Msg)
	resp.SetReply(new(dns.Msg))
	resp.RecursionDesired = false
	resp.Answer = append(resp.Answer, &dns.A{
		Hdr: dns.RR_Header{Name: "example.com.", Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 300},
		A:   net.ParseIP("93.184.216.34"),
	})

	exchangeFn := func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		if msg.RecursionDesired {
			t.Error("iterative query should have RecursionDesired=false")
		}
		return resp.Copy(), nil
	}

	cfg := &QueryConfig{
		UDPSize: 2048,
		Retries: 1,
		UseTCP:  false,
	}

	server := net.ParseIP("8.8.8.8")
	result, err := IterativeQueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(result.Answer) != 1 {
		t.Fatalf("expected 1 answer, got %d", len(result.Answer))
	}
}

func TestIterativeQueryWithExchangeNilConfig(t *testing.T) {
	resp := new(dns.Msg)
	resp.SetReply(new(dns.Msg))

	exchangeFn := func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		return resp.Copy(), nil
	}

	server := net.ParseIP("8.8.8.8")
	_, err := IterativeQueryWithExchange(context.Background(), server, "example.com", TypeA, nil, exchangeFn)
	if err != nil {
		t.Fatalf("unexpected error with nil config: %v", err)
	}
}

func TestIterativeQueryWithExchangeNilResponse(t *testing.T) {
	var mu sync.Mutex
	callCount := 0
	exchangeFn := func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		mu.Lock()
		callCount++
		mu.Unlock()
		return nil, nil
	}

	cfg := &QueryConfig{
		UDPSize: 2048,
		Retries: 2,
		UseTCP:  false,
	}

	server := net.ParseIP("8.8.8.8")
	_, err := IterativeQueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
	if err == nil {
		t.Fatal("expected error when response is nil")
	}
	if callCount != 2 {
		t.Errorf("expected 2 attempts, got %d", callCount)
	}
}

func TestIterativeQueryWithExchangeTCPFallback(t *testing.T) {
	truncated := new(dns.Msg)
	truncated.Truncated = true
	truncated.SetReply(new(dns.Msg))

	full := new(dns.Msg)
	full.SetReply(new(dns.Msg))
	full.Answer = append(full.Answer, &dns.A{
		Hdr: dns.RR_Header{Name: "example.com.", Rrtype: dns.TypeA},
		A:   net.ParseIP("1.2.3.4"),
	})

	var mu sync.Mutex
	calls := []bool{}
	exchangeFn := func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		mu.Lock()
		calls = append(calls, useTCP)
		mu.Unlock()
		if !useTCP {
			return truncated.Copy(), nil
		}
		return full.Copy(), nil
	}

	cfg := &QueryConfig{
		UDPSize:  2048,
		Retries:  1,
		UseTCP:   false,
		AllowTCP: true,
	}

	server := net.ParseIP("8.8.8.8")
	result, err := IterativeQueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(calls) != 2 {
		t.Errorf("expected 2 calls (UDP + TCP), got %d", len(calls))
	}
	if len(result.Answer) != 1 {
		t.Fatalf("expected 1 answer, got %d", len(result.Answer))
	}
}

func TestIterativeQueryWithExchangeAlwaysTCP(t *testing.T) {
	resp := new(dns.Msg)
	resp.SetReply(new(dns.Msg))

	var mu sync.Mutex
	calls := []bool{}
	exchangeFn := func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		mu.Lock()
		calls = append(calls, useTCP)
		mu.Unlock()
		return resp.Copy(), nil
	}

	cfg := &QueryConfig{
		UDPSize: 2048,
		Retries: 1,
		UseTCP:  true,
	}

	server := net.ParseIP("8.8.8.8")
	_, err := IterativeQueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(calls) != 1 || !calls[0] {
		t.Errorf("expected single TCP call, got %v", calls)
	}
}

func TestIterativeQueryWithExchangeRetriesOnFailure(t *testing.T) {
	var mu sync.Mutex
	callCount := 0
	exchangeFn := func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		mu.Lock()
		callCount++
		mu.Unlock()
		return nil, errors.New("connection refused")
	}

	cfg := &QueryConfig{
		UDPSize: 2048,
		Retries: 3,
		UseTCP:  false,
	}

	server := net.ParseIP("8.8.8.8")
	_, err := IterativeQueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
	if err == nil {
		t.Fatal("expected error")
	}
	if callCount != 3 {
		t.Errorf("expected 3 calls, got %d", callCount)
	}
}

func TestIterativeQueryWithExchangeContextCancel(t *testing.T) {
	ctx, cancel := context.WithCancel(context.Background())
	cancel()

	exchangeFn := func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		return nil, ctx.Err()
	}

	cfg := &QueryConfig{
		UDPSize: 2048,
		Retries: 1,
		UseTCP:  false,
	}

	server := net.ParseIP("8.8.8.8")
	_, err := IterativeQueryWithExchange(ctx, server, "example.com", TypeA, cfg, exchangeFn)
	if err == nil {
		t.Fatal("expected error on cancelled context")
	}
}

func TestExtractNSNames(t *testing.T) {
	rrs := []dns.RR{
		&dns.NS{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS}, Ns: "a.root-servers.net."},
		&dns.NS{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS}, Ns: "b.root-servers.net."},
	}
	names := extractNSNames(rrs)
	if len(names) != 2 {
		t.Fatalf("expected 2 names, got %d", len(names))
	}
}

func TestExtractNSNamesEmpty(t *testing.T) {
	names := extractNSNames(nil)
	if len(names) != 0 {
		t.Errorf("expected 0 names, got %d", len(names))
	}
}

func TestIterativeQueryWithExchangeZeroUDPSize(t *testing.T) {
	resp := new(dns.Msg)
	resp.SetReply(new(dns.Msg))

	exchangeFn := func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		return resp.Copy(), nil
	}

	cfg := &QueryConfig{
		UDPSize: 0, // should use default
		Retries: 1,
	}

	server := net.ParseIP("8.8.8.8")
	_, err := IterativeQueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
}