package synthetic

import (
	"context"
	"net"
	"testing"

	"github.com/coredns/coredns/plugin/pkg/dnstest"
	"github.com/coredns/coredns/plugin/test"
	"github.com/miekg/dns"
)

// testCase describes a single DNS query and the expected response.
type testCase struct {
	name       string
	qname      string
	qtype      uint16
	wantRcode  int
	wantAnswer []string
	wantTTL    uint32
}

// assertResponse validates the DNS response from ServeDNS against tc.
func assertResponse(t *testing.T, tc testCase, rc int, w *dnstest.Recorder) {
	t.Helper()

	if rc != tc.wantRcode {
		t.Errorf("rcode: got %d, want %d", rc, tc.wantRcode)
	}

	if tc.wantAnswer == nil {
		if len(w.Msg.Answer) > 0 {
			t.Errorf("answer: got %v, want none", w.Msg.Answer[0])
		}
		return
	}

	if len(w.Msg.Answer) == 0 {
		t.Fatal("answer: got none, want an answer")
	}

	hdr := w.Msg.Answer[0].Header()
	if hdr.Name != tc.qname {
		t.Errorf("name: got %s, want %s", hdr.Name, tc.qname)
	}
	if hdr.Rrtype != tc.qtype {
		t.Errorf("rrtype: got %d, want %d", hdr.Rrtype, tc.qtype)
	}
	if hdr.Ttl != tc.wantTTL {
		t.Errorf("ttl: got %d, want %d", hdr.Ttl, tc.wantTTL)
	}

	switch rr := w.Msg.Answer[0].(type) {
	case *dns.A:
		if rr.A.String() != tc.wantAnswer[0] {
			t.Errorf("A record: got %s, want %s", rr.A, tc.wantAnswer[0])
		}
	case *dns.AAAA:
		if rr.AAAA.String() != tc.wantAnswer[0] {
			t.Errorf("AAAA record: got %s, want %s", rr.AAAA, tc.wantAnswer[0])
		}
	case *dns.PTR:
		if rr.Ptr != tc.wantAnswer[0] {
			t.Errorf("PTR record: got %s, want %s", rr.Ptr, tc.wantAnswer[0])
		}
	}
}

// runTestCases executes a table of test cases against the given synthetic plugin.
func runTestCases(t *testing.T, s synthetic, cases []testCase) {
	t.Helper()
	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			w := dnstest.NewRecorder(&test.ResponseWriter{})
			r := new(dns.Msg)
			r.SetQuestion(tc.qname, tc.qtype)

			rc, err := s.ServeDNS(context.TODO(), w, r)
			if err != nil {
				t.Fatalf("unexpected error: %v", err)
			}

			assertResponse(t, tc, rc, w)
		})
	}
}

func TestServeDNSv4(t *testing.T) {
	_, ipNet, err := net.ParseCIDR("192.0.2.0/24")
	if err != nil {
		t.Fatal(err)
	}

	s := synthetic{
		Next:   test.ErrorHandler(),
		Config: syntheticConfig{net: []*net.IPNet{ipNet}, forward: "example.com", prefix: "ip-"},
	}

	runTestCases(t, s, []testCase{
		{
			name:       "v4 first address",
			qname:      "ip-192-0-2-0.example.com",
			qtype:      dns.TypeA,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"192.0.2.0"},
		},
		{
			name:       "v4 last address",
			qname:      "ip-192-0-2-255.example.com",
			qtype:      dns.TypeA,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"192.0.2.255"},
		},
		{
			name:      "v4 out of range",
			qname:     "ip-203-0-113-100.example.com",
			qtype:     dns.TypeA,
			wantRcode: dns.RcodeServerFailure,
		},
		{
			name:       "v4 PTR reverse",
			qname:      "123.2.0.192.in-addr.arpa.",
			qtype:      dns.TypePTR,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"ip-192-0-2-123.example.com."},
		},
		{
			name:      "v6 address with v4 config",
			qname:     "ip-2001-db8-abcd--.example.com",
			qtype:     dns.TypeA,
			wantRcode: dns.RcodeServerFailure,
		},
	})
}

func TestServeDNSv6(t *testing.T) {
	_, ipNet, err := net.ParseCIDR("2001:db8:abcd::/48")
	if err != nil {
		t.Fatal(err)
	}

	s := synthetic{
		Next: test.ErrorHandler(),
		Config: syntheticConfig{
			net:     []*net.IPNet{ipNet},
			forward: "example.com.",
			ttl:     1800,
			prefix:  "ip6-",
		},
	}

	runTestCases(t, s, []testCase{
		{
			name:       "v6 zero-padded",
			qname:      "ip6-2001-db8-abcd--.example.com",
			qtype:      dns.TypeAAAA,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"2001:db8:abcd::"},
			wantTTL:    1800,
		},
		{
			name:       "v6 fully expanded",
			qname:      "ip6-2001-db8-abcd-1234-4567-890a-bcde-f123.example.com",
			qtype:      dns.TypeAAAA,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"2001:db8:abcd:1234:4567:890a:bcde:f123"},
			wantTTL:    1800,
		},
		{
			name:      "v6 out of range",
			qname:     "ip6-2001-db8-1234--.example.com",
			qtype:     dns.TypeAAAA,
			wantRcode: dns.RcodeServerFailure,
		},
		{
			name:       "v6 PTR reverse",
			qname:      "3.2.1.f.e.d.c.b.a.0.9.8.7.6.5.4.4.3.2.1.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa.",
			qtype:      dns.TypePTR,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"ip6-2001-db8-abcd-1234-4567-890a-bcde-f123.example.com."},
			wantTTL:    1800,
		},
		{
			name:      "v4 address with v6 config",
			qname:     "ip6-192-0-2-0.example.com",
			qtype:     dns.TypeAAAA,
			wantRcode: dns.RcodeServerFailure,
		},
	})
}

// mockSuccessPlugin always returns a successful answer, simulating a static
// zone file or upstream resolver that provides authoritative records.
type mockSuccessPlugin struct{}

func (m mockSuccessPlugin) Name() string { return "mock" }

func (m mockSuccessPlugin) ServeDNS(_ context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
	msg := new(dns.Msg)
	msg.SetReply(r)
	hdr := dns.RR_Header{
		Name:   r.Question[0].Name,
		Rrtype: r.Question[0].Qtype,
		Class:  r.Question[0].Qclass,
	}

	switch r.Question[0].Qtype {
	case dns.TypeA:
		msg.Answer = append(msg.Answer, &dns.A{Hdr: hdr, A: net.ParseIP("192.0.2.100")})
	case dns.TypeAAAA:
		msg.Answer = append(msg.Answer, &dns.AAAA{Hdr: hdr, AAAA: net.ParseIP("2001:db8::100")})
	}

	w.WriteMsg(msg)
	return dns.RcodeSuccess, nil
}

// TestServeDNSNextPluginPrecedence verifies that answers from the next plugin
// in the chain take priority over synthetic responses for reverse lookups,
// while forward lookups still produce synthetic answers directly.
func TestServeDNSNextPluginPrecedence(t *testing.T) {
	_, ipNet4, err := net.ParseCIDR("192.0.2.0/24")
	if err != nil {
		t.Fatal(err)
	}
	_, ipNet6, err := net.ParseCIDR("2001:db8:abcd::/48")
	if err != nil {
		t.Fatal(err)
	}

	s := synthetic{
		Next: mockSuccessPlugin{},
		Config: syntheticConfig{
			net:     []*net.IPNet{ipNet4, ipNet6},
			forward: "example.com",
			prefix:  "ip-",
		},
	}

	runTestCases(t, s, []testCase{
		{
			name:       "forward v4 synthetic wins",
			qname:      "ip-192-0-2-1.example.com",
			qtype:      dns.TypeA,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"192.0.2.1"},
		},
		{
			name:       "forward non-synthetic uses next plugin",
			qname:      "foobar.example.com",
			qtype:      dns.TypeA,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"192.0.2.100"},
		},
		{
			name:       "forward v6 synthetic wins",
			qname:      "ip-2001-db8-abcd--1.example.com",
			qtype:      dns.TypeAAAA,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"2001:db8:abcd::1"},
		},
		{
			name:       "forward non-synthetic AAAA uses next plugin",
			qname:      "foobar.example.com",
			qtype:      dns.TypeAAAA,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"2001:db8::100"},
		},
		{
			name:      "v6 address queried as A returns empty",
			qname:     "ip-2001-db8-abcd--1.example.com",
			qtype:     dns.TypeA,
			wantRcode: dns.RcodeSuccess,
		},
		{
			name:      "v4 address queried as AAAA returns empty",
			qname:     "ip-192-0-2-1.example.com",
			qtype:     dns.TypeAAAA,
			wantRcode: dns.RcodeSuccess,
		},
		{
			name:       "PTR v6 synthetic (mock has no PTR)",
			qname:      "3.2.1.f.e.d.c.b.a.0.9.8.7.6.5.4.4.3.2.1.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa.",
			qtype:      dns.TypePTR,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"ip-2001-db8-abcd-1234-4567-890a-bcde-f123.example.com."},
		},
		{
			name:       "PTR v4 synthetic (mock has no PTR)",
			qname:      "123.2.0.192.in-addr.arpa.",
			qtype:      dns.TypePTR,
			wantRcode:  dns.RcodeSuccess,
			wantAnswer: []string{"ip-192-0-2-123.example.com."},
		},
	})
}