package dns

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

	"github.com/miekg/dns"
)

type mockResolver struct {
	mu       sync.Mutex
	calls    int
	response *dns.Msg
	err      error
}

func (m *mockResolver) Query(ctx context.Context, server net.IP, name string, qtype uint16, cfg *QueryConfig) (*dns.Msg, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.calls++
	if m.err != nil {
		return nil, m.err
	}
	if m.response != nil {
		return m.response.Copy(), nil
	}
	return nil, errors.New("no response configured")
}

func (m *mockResolver) callCount() int {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.calls
}

func makeResponse(name string, qtype uint16, ttl uint32) *dns.Msg {
	resp := new(dns.Msg)
	resp.SetReply(new(dns.Msg))
	switch qtype {
	case dns.TypeA:
		resp.Answer = append(resp.Answer, &dns.A{
			Hdr: dns.RR_Header{Name: dns.Fqdn(name), Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: ttl},
			A:   net.ParseIP("93.184.216.34"),
		})
	case dns.TypeNS:
		resp.Answer = append(resp.Answer, &dns.NS{
			Hdr: dns.RR_Header{Name: dns.Fqdn(name), Rrtype: dns.TypeNS, Class: dns.ClassINET, Ttl: ttl},
			Ns:  "ns1.example.com.",
		})
	}
	return resp
}

func TestNewCachingResolver_NilInner(t *testing.T) {
	cr := NewCachingResolver(nil)
	if cr == nil {
		t.Fatal("NewCachingResolver(nil) returned nil")
	}
	if cr.inner == nil {
		t.Fatal("expected inner resolver to be set when nil passed")
	}
}

func TestCachingResolver_CacheHit(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)

	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	resp1, err := cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if err != nil {
		t.Fatalf("first query: %v", err)
	}
	if mock.callCount() != 1 {
		t.Fatalf("expected 1 call after first query, got %d", mock.callCount())
	}

	resp2, err := cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if err != nil {
		t.Fatalf("second query: %v", err)
	}
	if mock.callCount() != 1 {
		t.Fatalf("expected still 1 call after second query (cache hit), got %d", mock.callCount())
	}

	if len(resp1.Answer) != len(resp2.Answer) {
		t.Errorf("cached response has different number of answers")
	}
}

func TestCachingResolver_CacheMissDifferentServer(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)

	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	_, _ = cr.Query(context.Background(), net.ParseIP("8.8.8.8"), "example.com", TypeA, cfg)
	if mock.callCount() != 1 {
		t.Fatalf("expected 1 call, got %d", mock.callCount())
	}

	_, _ = cr.Query(context.Background(), net.ParseIP("1.1.1.1"), "example.com", TypeA, cfg)
	if mock.callCount() != 2 {
		t.Fatalf("expected 2 calls for different server, got %d", mock.callCount())
	}
}

func TestCachingResolver_CacheMissDifferentName(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	_, _ = cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if mock.callCount() != 1 {
		t.Fatalf("expected 1 call, got %d", mock.callCount())
	}

	_, _ = cr.Query(context.Background(), server, "different.com", TypeA, cfg)
	if mock.callCount() != 2 {
		t.Fatalf("expected 2 calls for different name, got %d", mock.callCount())
	}
}

func TestCachingResolver_CacheMissDifferentType(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	_, _ = cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if mock.callCount() != 1 {
		t.Fatalf("expected 1 call, got %d", mock.callCount())
	}

	_, _ = cr.Query(context.Background(), server, "example.com", TypeNS, cfg)
	if mock.callCount() != 2 {
		t.Fatalf("expected 2 calls for different qtype, got %d", mock.callCount())
	}
}

func TestCachingResolver_ErrorNotCached(t *testing.T) {
	mock := &mockResolver{
		err: errors.New("connection refused"),
	}
	cr := NewCachingResolver(mock)
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	_, err := cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if err == nil {
		t.Fatal("expected error from mock")
	}

	mock.err = nil
	mock.response = makeResponse("example.com", dns.TypeA, 300)

	_, err = cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if err != nil {
		t.Fatalf("second query after mock fixed: %v", err)
	}
	if mock.callCount() != 2 {
		t.Fatalf("expected 2 calls (error not cached), got %d", mock.callCount())
	}
}

func TestCachingResolver_TTLExpiry(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 1),
	}
	cr := NewCachingResolver(mock, WithDefaultTTL(1*time.Second))
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	_, err := cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if err != nil {
		t.Fatalf("first query: %v", err)
	}
	if mock.callCount() != 1 {
		t.Fatalf("expected 1 call, got %d", mock.callCount())
	}

	time.Sleep(2 * time.Second)

	_, err = cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if err != nil {
		t.Fatalf("query after TTL expiry: %v", err)
	}
	if mock.callCount() != 2 {
		t.Fatalf("expected 2 calls after TTL expiry, got %d", mock.callCount())
	}
}

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

	mock := &mockResolver{response: resp}
	cr := NewCachingResolver(mock, WithDefaultTTL(100*time.Millisecond))
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	_, err := cr.Query(context.Background(), server, "nodata.com", TypeA, cfg)
	if err != nil {
		t.Fatalf("first query: %v", err)
	}

	time.Sleep(150 * time.Millisecond)

	_, err = cr.Query(context.Background(), server, "nodata.com", TypeA, cfg)
	if err != nil {
		t.Fatalf("query after default TTL expiry: %v", err)
	}
	if mock.callCount() != 2 {
		t.Fatalf("expected 2 calls after default TTL, got %d", mock.callCount())
	}
}

func TestCachingResolver_NilConfig(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)

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

func TestCachingResolver_Len(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)
	if cr.Len() != 0 {
		t.Fatalf("expected empty cache, got %d", cr.Len())
	}

	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}
	_, _ = cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if cr.Len() != 1 {
		t.Fatalf("expected cache len 1, got %d", cr.Len())
	}

	_, _ = cr.Query(context.Background(), server, "other.com", TypeA, cfg)
	if cr.Len() != 2 {
		t.Fatalf("expected cache len 2, got %d", cr.Len())
	}
}

func TestCachingResolver_Clear(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	_, _ = cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	_, _ = cr.Query(context.Background(), server, "other.com", TypeA, cfg)
	if cr.Len() != 2 {
		t.Fatalf("expected cache len 2, got %d", cr.Len())
	}

	cr.Clear()
	if cr.Len() != 0 {
		t.Fatalf("expected cache len 0 after clear, got %d", cr.Len())
	}

	_, err := cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if err != nil {
		t.Fatalf("query after clear: %v", err)
	}
	if mock.callCount() != 3 {
		t.Fatalf("expected 3 calls (2 before clear + 1 after clear), got %d", mock.callCount())
	}
}

func TestCachingResolver_PurgeExpired(t *testing.T) {
	resp := makeResponse("example.com", dns.TypeA, 0)
	for _, rr := range resp.Answer {
		rr.Header().Ttl = 0
	}
	mock := &mockResolver{response: resp}
	cr := NewCachingResolver(mock, WithDefaultTTL(50*time.Millisecond))
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	_, _ = cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	if cr.Len() != 1 {
		t.Fatalf("expected cache len 1, got %d", cr.Len())
	}

	time.Sleep(100 * time.Millisecond)

	purged := cr.PurgeExpired()
	if purged != 1 {
		t.Fatalf("expected 1 purged entry, got %d", purged)
	}
	if cr.Len() != 0 {
		t.Fatalf("expected cache len 0 after purge, got %d", cr.Len())
	}
}

func TestCachingResolver_PurgeExpiredNoneExpired(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	_, _ = cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	purged := cr.PurgeExpired()
	if purged != 0 {
		t.Fatalf("expected 0 purged entries, got %d", purged)
	}
	if cr.Len() != 1 {
		t.Fatalf("expected cache len 1, got %d", cr.Len())
	}
}

func TestCachingResolver_ResponseCopy(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	resp1, _ := cr.Query(context.Background(), server, "example.com", TypeA, cfg)
	resp2, _ := cr.Query(context.Background(), server, "example.com", TypeA, cfg)

	if resp1 == resp2 {
		t.Fatal("cache should return a copy, not the same pointer")
	}
}

func TestCachingResolver_MinTTLFromMsg(t *testing.T) {
	tests := []struct {
		name     string
		msg      *dns.Msg
		expected time.Duration
	}{
		{
			name:     "nil message",
			msg:      nil,
			expected: 0,
		},
		{
			name:     "empty response",
			msg:      new(dns.Msg),
			expected: 0,
		},
		{
			name: "single answer with low TTL",
			msg: func() *dns.Msg {
				m := new(dns.Msg)
				m.Answer = append(m.Answer, &dns.A{
					Hdr: dns.RR_Header{Ttl: 60},
				})
				return m
			}(),
			expected: 60 * time.Second,
		},
		{
			name: "multiple records with varying TTLs",
			msg: func() *dns.Msg {
				m := new(dns.Msg)
				m.Answer = append(m.Answer, &dns.A{
					Hdr: dns.RR_Header{Ttl: 300},
				})
				m.Ns = append(m.Ns, &dns.NS{
					Hdr: dns.RR_Header{Ttl: 120},
				})
				return m
			}(),
			expected: 120 * time.Second,
		},
		{
			name: "OPT record excluded from TTL calculation",
			msg: func() *dns.Msg {
				m := new(dns.Msg)
				m.Answer = append(m.Answer, &dns.A{
					Hdr: dns.RR_Header{Ttl: 300},
				})
				m.Extra = append(m.Extra, &dns.OPT{
					Hdr: dns.RR_Header{Ttl: 0},
				})
				return m
			}(),
			expected: 300 * time.Second,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			got := minTTLFromMsg(tt.msg)
			if got != tt.expected {
				t.Errorf("minTTLFromMsg() = %v, want %v", got, tt.expected)
			}
		})
	}
}

func TestCachingResolver_ConcurrentAccess(t *testing.T) {
	mock := &mockResolver{
		response: makeResponse("example.com", dns.TypeA, 300),
	}
	cr := NewCachingResolver(mock)
	server := net.ParseIP("8.8.8.8")
	cfg := &QueryConfig{UDPSize: 2048, Retries: 1, Timeout: 5 * time.Second}

	var wg sync.WaitGroup
	for i := 0; i < 100; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			_, err := cr.Query(context.Background(), server, "example.com", TypeA, cfg)
			if err != nil {
				t.Errorf("concurrent query failed: %v", err)
			}
		}()
	}
	wg.Wait()

	if mock.callCount() < 1 {
		t.Fatalf("expected at least 1 call to mock, got %d", mock.callCount())
	}
}

func TestBasicResolver(t *testing.T) {
	br := NewBasicResolver()
	if br == nil {
		t.Fatal("NewBasicResolver returned nil")
	}

	if _, ok := interface{}(br).(Resolver); !ok {
		t.Fatal("BasicResolver does not implement Resolver interface")
	}
}

// TestBasicResolverQueryIntegration calls Query via the BasicResolver against
// the local system resolver. Skipped when no local resolver is reachable.
func TestBasicResolverQueryIntegration(t *testing.T) {
r := NewBasicResolver()
server := net.ParseIP("127.0.0.1")
ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()

// Cover BasicResolver.Query; skip if 127.0.0.1:53 is not available.
msg, err := r.Query(ctx, server, ".", TypeNS, nil)
if err != nil {
t.Logf("skipping (local resolver unavailable): %v", err)
t.Skip()
}
if msg == nil {
t.Fatal("expected non-nil response from BasicResolver.Query")
}
}