package dns

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

	"github.com/miekg/dns"
)

func TestDefaultQueryConfig(t *testing.T) {
	cfg := DefaultQueryConfig()
	if cfg == nil {
		t.Fatal("DefaultQueryConfig returned nil")
	}
	if cfg.UDPSize != 2048 {
		t.Errorf("UDPSize = %d, want 2048", cfg.UDPSize)
	}
	if cfg.Retries != 3 {
		t.Errorf("Retries = %d, want 3", cfg.Retries)
	}
	if cfg.UseTCP {
		t.Error("UseTCP should be false by default")
	}
}

func TestBuildQuery(t *testing.T) {
	msg := buildQuery("example.com.", TypeA, 2048)
	if len(msg.Question) != 1 {
		t.Fatalf("expected 1 question, got %d", len(msg.Question))
	}
	q := msg.Question[0]
	if q.Name != "example.com." {
		t.Errorf("question name = %q, want %q", q.Name, "example.com.")
	}
	if q.Qtype != TypeA {
		t.Errorf("question type = %d, want %d", q.Qtype, TypeA)
	}
	if !msg.RecursionDesired {
		t.Error("RecursionDesired should be true")
	}
	if opt := msg.IsEdns0(); opt == nil {
		t.Error("expected EDNS0 OPT record")
	} else if opt.UDPSize() != 2048 {
		t.Errorf("EDNS0 UDPSize = %d, want 2048", opt.UDPSize())
	}
}

func TestBuildQueryFqdn(t *testing.T) {
	msg := buildQuery("example.com", TypeA, 4096)
	q := msg.Question[0]
	if q.Name != "example.com." {
		t.Errorf("Fqdn not applied: got %q, want %q", q.Name, "example.com.")
	}
}

func TestQueryWithExchangeSuccess(t *testing.T) {
	expectedResp := new(dns.Msg)
	expectedResp.SetReply(new(dns.Msg))
	expectedResp.Answer = append(expectedResp.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) {
		return expectedResp.Copy(), nil
	}

	cfg := &QueryConfig{
		UDPSize: 2048,
		Timeout: 5,
		Retries: 1,
		UseTCP:  false,
	}

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

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

	fullResp := new(dns.Msg)
	fullResp.SetReply(new(dns.Msg))
	fullResp.Answer = append(fullResp.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"),
	})

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

	cfg := &QueryConfig{
		UDPSize: 2048,
		Timeout: 5,
		Retries: 1,
		UseTCP:  false,
	}

	server := net.ParseIP("8.8.8.8")
	resp, err := QueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(calls) != 2 {
		t.Fatalf("expected 2 exchange calls (UDP then TCP), got %d", len(calls))
	}
	if calls[0] != false {
		t.Error("first call should be UDP")
	}
	if calls[1] != true {
		t.Error("second call should be TCP")
	}
	if len(resp.Answer) != 1 {
		t.Fatalf("expected 1 answer from TCP fallback, got %d", len(resp.Answer))
	}
}

func TestQueryAlwaysTCP(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()
		defer mu.Unlock()
		calls = append(calls, useTCP)
		return resp.Copy(), nil
	}

	cfg := &QueryConfig{
		UDPSize: 2048,
		Timeout: 5,
		Retries: 1,
		UseTCP:  true,
	}

	server := net.ParseIP("8.8.8.8")
	_, err := QueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(calls) != 1 {
		t.Fatalf("expected 1 exchange call, got %d", len(calls))
	}
	if !calls[0] {
		t.Error("expected TCP call when UseTCP is true")
	}
}

func TestQueryRetriesOnFailure(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,
		Timeout: 5,
		Retries: 3,
		UseTCP:  false,
	}

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

func TestQueryContextCancellation(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,
		Timeout: 5,
		Retries: 1,
		UseTCP:  false,
	}

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

func TestQueryNilConfigUsesDefaults(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 := QueryWithExchange(context.Background(), server, "example.com", TypeA, nil, exchangeFn)
	if err != nil {
		t.Fatalf("unexpected error with nil config: %v", err)
	}
}

func TestQueryZeroValuesUseDefaults(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,
		Timeout: 0,
		Retries: 1,
		UseTCP:  false,
	}

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

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

	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()
		if !useTCP {
			return truncatedResp.Copy(), nil
		}
		return nil, errors.New("tcp failed")
	}

	cfg := &QueryConfig{
		UDPSize: 2048,
		Timeout: 5,
		Retries: 2,
		UseTCP:  false,
	}

	server := net.ParseIP("8.8.8.8")
	_, err := QueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
	if err == nil {
		t.Fatal("expected error when TCP fallback always fails")
	}
	if callCount != 4 {
		t.Errorf("expected 4 calls (2 retries x UDP+TCP), got %d", callCount)
	}
}