package dns

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

	"github.com/miekg/dns"
)

// testClient returns a Client with fast retries wired to fn.
func testClient(cfg *QueryConfig, fn ExchangeFunc) *Client {
	if cfg == nil {
		cfg = DefaultQueryConfig()
	}
	cfg.Timeout = time.Second
	cfg.RetryDelay = time.Millisecond
	return NewClient(cfg, fn)
}

func answerMsg(name string, ip string) *dns.Msg {
	m := new(dns.Msg)
	m.SetReply(new(dns.Msg))
	m.Answer = append(m.Answer, &dns.A{
		Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 300},
		A:   net.ParseIP(ip),
	})
	return m
}

func TestDefaultQueryConfig(t *testing.T) {
	cfg := DefaultQueryConfig()
	if cfg.UDPSize != 2048 {
		t.Errorf("UDPSize = %d, want 2048", cfg.UDPSize)
	}
	if cfg.Retries != 2 {
		t.Errorf("Retries = %d, want 2", cfg.Retries)
	}
	if cfg.Timeout != 2*time.Second {
		t.Errorf("Timeout = %v, want 2s", cfg.Timeout)
	}
	if cfg.RetryDelay != 2*time.Second {
		t.Errorf("RetryDelay = %v, want 2s", cfg.RetryDelay)
	}
	if cfg.UseTCP {
		t.Error("UseTCP should be false by default")
	}
	if !cfg.AllowTCP {
		t.Error("AllowTCP should be true by default")
	}
}

func TestBuildQueryRDZeroWithEDNS(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("Fqdn not applied: got %q", q.Name)
	}
	if q.Qtype != TypeA {
		t.Errorf("question type = %d, want %d", q.Qtype, TypeA)
	}
	if msg.RecursionDesired {
		t.Error("RecursionDesired must be false on the query path")
	}
	opt := msg.IsEdns0()
	if opt == nil {
		t.Fatal("expected EDNS0 OPT record for udpsize > 512")
	}
	if opt.UDPSize() != 2048 {
		t.Errorf("EDNS0 UDPSize = %d, want 2048", opt.UDPSize())
	}
}

func TestBuildQueryNoEDNSAt512(t *testing.T) {
	msg := buildQuery("example.com.", TypeA, 512)
	if msg.IsEdns0() != nil {
		t.Error("no OPT record should be attached when udpsize <= 512")
	}
}

func TestClientQuerySuccess(t *testing.T) {
	c := testClient(nil, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		if msg.RecursionDesired {
			t.Error("query must be sent with RD=0")
		}
		return answerMsg("example.com.", "93.184.216.34"), nil
	})

	resp, warnings, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(resp.Answer) != 1 {
		t.Fatalf("expected 1 answer, got %d", len(resp.Answer))
	}
	if len(warnings) != 0 {
		t.Errorf("unexpected warnings: %v", warnings)
	}
}

func TestClientPacketCache(t *testing.T) {
	var calls int
	c := testClient(nil, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		calls++
		return answerMsg("example.com.", "1.2.3.4"), nil
	})

	ctx := context.Background()
	server := net.ParseIP("8.8.8.8")
	for i := 0; i < 3; i++ {
		if _, _, err := c.Query(ctx, server, "example.com", TypeA); err != nil {
			t.Fatalf("query %d: %v", i, err)
		}
	}
	if calls != 1 {
		t.Errorf("expected 1 wire query for repeat askers, got %d", calls)
	}
	if c.Requests() != 3 {
		t.Errorf("Requests = %d, want 3", c.Requests())
	}
	if c.CacheHits() != 2 {
		t.Errorf("CacheHits = %d, want 2", c.CacheHits())
	}
	// Case differences must hit the same cache entry.
	if _, _, err := c.Query(ctx, server, "EXAMPLE.COM.", TypeA); err != nil {
		t.Fatal(err)
	}
	if calls != 1 {
		t.Errorf("case-insensitive lookup should hit cache, got %d wire calls", calls)
	}
}

func TestClientPacketCacheDistinctKeys(t *testing.T) {
	var calls int
	c := testClient(nil, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		calls++
		return answerMsg("example.com.", "1.2.3.4"), nil
	})

	ctx := context.Background()
	_, _, _ = c.Query(ctx, net.ParseIP("8.8.8.8"), "example.com", TypeA)
	_, _, _ = c.Query(ctx, net.ParseIP("9.9.9.9"), "example.com", TypeA)
	_, _, _ = c.Query(ctx, net.ParseIP("8.8.8.8"), "example.com", TypeAAAA)
	_, _, _ = c.Query(ctx, net.ParseIP("8.8.8.8"), "other.com", TypeA)
	if calls != 4 {
		t.Errorf("expected 4 wire queries for 4 distinct keys, got %d", calls)
	}
}

func TestClientPacketCacheReplaysErrors(t *testing.T) {
	var calls int
	c := testClient(&QueryConfig{Retries: 1}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		calls++
		return nil, errors.New("connection refused")
	})

	ctx := context.Background()
	server := net.ParseIP("8.8.8.8")
	_, _, err1 := c.Query(ctx, server, "example.com", TypeA)
	_, _, err2 := c.Query(ctx, server, "example.com", TypeA)
	if err1 == nil || err2 == nil {
		t.Fatal("expected errors")
	}
	if calls != 1 {
		t.Errorf("failures must be cached too: got %d wire calls", calls)
	}
}

func TestClientEDNSFallback(t *testing.T) {
	var sizes []int
	c := testClient(nil, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		size := 512
		if opt := msg.IsEdns0(); opt != nil {
			size = int(opt.UDPSize())
		}
		sizes = append(sizes, size)
		m := new(dns.Msg)
		m.SetReply(msg)
		if size > 512 {
			m.Rcode = dns.RcodeFormatError
			return m, nil
		}
		m.Answer = append(m.Answer, &dns.A{
			Hdr: dns.RR_Header{Name: "example.com.", Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 300},
			A:   net.ParseIP("1.2.3.4"),
		})
		return m, nil
	})

	resp, warnings, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(sizes) != 2 || sizes[0] != 2048 || sizes[1] != 512 {
		t.Fatalf("expected 2048 then 512 queries, got %v", sizes)
	}
	if resp.Rcode != dns.RcodeSuccess || len(resp.Answer) != 1 {
		t.Error("expected the 512-byte retry response to be returned")
	}
	want := "8.8.8.8 doesn't seem to support EDNS0"
	if len(warnings) != 1 || warnings[0] != want {
		t.Errorf("warnings = %v, want [%q]", warnings, want)
	}
}

func TestClientEDNSFallbackKeepsOriginalWhenRetryFails(t *testing.T) {
	c := testClient(nil, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		m := new(dns.Msg)
		m.SetReply(msg)
		m.Rcode = dns.RcodeServerFailure
		return m, nil
	})

	resp, warnings, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if resp.Rcode != dns.RcodeServerFailure {
		t.Errorf("expected original SERVFAIL response, got rcode %d", resp.Rcode)
	}
	if len(warnings) != 0 {
		t.Errorf("no EDNS0 warning expected when the retry also fails: %v", warnings)
	}
}

func TestClientNoEDNSFallbackAt512(t *testing.T) {
	var calls int
	c := testClient(&QueryConfig{UDPSize: 512, Retries: 1}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		calls++
		m := new(dns.Msg)
		m.SetReply(msg)
		m.Rcode = dns.RcodeFormatError
		return m, nil
	})

	resp, _, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if calls != 1 {
		t.Errorf("expected no fallback query at udpsize 512, got %d calls", calls)
	}
	if resp.Rcode != dns.RcodeFormatError {
		t.Errorf("expected FORMERR passthrough, got %d", resp.Rcode)
	}
}

func TestClientRecursionAvailableWarning(t *testing.T) {
	c := testClient(nil, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		m := answerMsg("example.com.", "1.2.3.4")
		m.RecursionAvailable = true
		return m, nil
	})

	_, warnings, err := c.Query(context.Background(), net.ParseIP("192.0.2.1"), "example.com", TypeA)
	if err != nil {
		t.Fatal(err)
	}
	want := "192.0.2.1 allows recursion"
	if len(warnings) != 1 || warnings[0] != want {
		t.Errorf("warnings = %v, want [%q]", warnings, want)
	}
}

func TestClientTruncationWarningWhenTCPDisallowed(t *testing.T) {
	c := testClient(&QueryConfig{AllowTCP: false, Retries: 1}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		if useTCP {
			t.Error("TCP must not be used when AllowTCP is false")
		}
		m := answerMsg("example.com.", "1.2.3.4")
		m.Truncated = true
		return m, nil
	})

	resp, warnings, err := c.Query(context.Background(), net.ParseIP("192.0.2.1"), "example.com", TypeA)
	if err != nil {
		t.Fatal(err)
	}
	if !resp.Truncated {
		t.Error("expected truncated response to be returned as-is")
	}
	want := "192.0.2.1 sent truncated packet"
	if len(warnings) != 1 || warnings[0] != want {
		t.Errorf("warnings = %v, want [%q]", warnings, want)
	}
}

func TestClientTCPFallbackOnTruncation(t *testing.T) {
	var mu sync.Mutex
	var calls []bool
	c := testClient(nil, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		mu.Lock()
		calls = append(calls, useTCP)
		mu.Unlock()
		if !useTCP {
			m := new(dns.Msg)
			m.SetReply(msg)
			m.Truncated = true
			return m, nil
		}
		return answerMsg("example.com.", "93.184.216.34"), nil
	})

	resp, warnings, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(calls) != 2 || calls[0] != false || calls[1] != true {
		t.Fatalf("expected UDP then TCP, got %v", calls)
	}
	if len(resp.Answer) != 1 {
		t.Fatal("expected answer from TCP fallback")
	}
	if len(warnings) != 0 {
		t.Errorf("unexpected warnings after successful TCP fallback: %v", warnings)
	}
}

func TestClientAlwaysTCP(t *testing.T) {
	var mu sync.Mutex
	var calls []bool
	c := testClient(&QueryConfig{UseTCP: true, Retries: 1}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		mu.Lock()
		calls = append(calls, useTCP)
		mu.Unlock()
		return answerMsg("example.com.", "1.2.3.4"), nil
	})

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

func TestClientRetriesAreTotalAttempts(t *testing.T) {
	var calls int
	c := testClient(&QueryConfig{Retries: 3}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		calls++
		return nil, errors.New("connection refused")
	})

	_, _, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err == nil {
		t.Fatal("expected error after retries exhausted")
	}
	// dnsruby retry_times counts total transmissions, not extra retries.
	if calls != 3 {
		t.Errorf("expected 3 attempts, got %d", calls)
	}
	if !strings.Contains(err.Error(), "after 3 attempts") {
		t.Errorf("error should mention attempt count: %v", err)
	}
}

func TestClientZeroRetriesStillQueriesOnce(t *testing.T) {
	var calls int
	c := testClient(&QueryConfig{Retries: 0}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		calls++
		return nil, errors.New("boom")
	})

	_, _, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err == nil {
		t.Fatal("expected error")
	}
	if calls != 1 {
		t.Errorf("Retries=0 must be clamped to one attempt, got %d", calls)
	}
	// Regression: the old code produced "failed after 0 retries: %!w(<nil>)".
	if strings.Contains(err.Error(), "%!w") || strings.Contains(err.Error(), "<nil>") {
		t.Errorf("malformed error message: %v", err)
	}
}

func TestClientRetryThenSuccess(t *testing.T) {
	var calls int
	c := testClient(&QueryConfig{Retries: 3}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		calls++
		if calls < 2 {
			return nil, errors.New("transient error")
		}
		return answerMsg("example.com.", "1.2.3.4"), nil
	})

	resp, _, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(resp.Answer) == 0 {
		t.Fatal("expected answer after retry")
	}
	if calls != 2 {
		t.Errorf("expected 2 attempts, got %d", calls)
	}
}

func TestClientNilResponseIsError(t *testing.T) {
	c := testClient(&QueryConfig{Retries: 2}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		return nil, nil
	})

	_, _, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err == nil {
		t.Fatal("expected error for nil responses")
	}
}

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

	c := testClient(&QueryConfig{Retries: 5}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		return nil, errors.New("error")
	})

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

func TestClientNilConfigUsesDefaults(t *testing.T) {
	c := NewClient(nil, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		return answerMsg("example.com.", "1.2.3.4"), nil
	})
	_, _, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err != nil {
		t.Fatalf("unexpected error with nil config: %v", err)
	}
}

func TestClientTCPFallbackFailureRetries(t *testing.T) {
	var calls int
	c := testClient(&QueryConfig{Retries: 2, AllowTCP: true}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		calls++
		if !useTCP {
			m := new(dns.Msg)
			m.SetReply(msg)
			m.Truncated = true
			return m, nil
		}
		return nil, errors.New("tcp failed")
	})

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

func TestRetryGap(t *testing.T) {
	d := 2 * time.Second
	tests := []struct {
		retry int
		want  time.Duration
	}{
		{1, 4 * time.Second}, // dnsruby sends retry 1 at absolute 2d
		{2, 4 * time.Second}, // retry 2 at 4d → gap 2d
		{3, 8 * time.Second},
		{4, 16 * time.Second},
	}
	for _, tt := range tests {
		got := retryGap(d, tt.retry)
		if got != tt.want {
			t.Errorf("retryGap(%v, %d) = %v, want %v", d, tt.retry, got, tt.want)
		}
	}
}

func TestQueryErrorMessageMentionsQuery(t *testing.T) {
	c := testClient(&QueryConfig{Retries: 1}, func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
		return nil, errors.New("unreachable")
	})
	_, _, err := c.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA)
	if err == nil {
		t.Fatal("expected error")
	}
	for _, part := range []string{"example.com.", "A", "8.8.8.8", "unreachable"} {
		if !strings.Contains(err.Error(), part) {
			t.Errorf("error %q should contain %q", err, part)
		}
	}
}