package dns

import (
	"context"
	"net"
	"testing"
	"time"

	"github.com/miekg/dns"
)

func TestRootServerAllIPs(t *testing.T) {
	rs := RootServer{
		Name: "a.root-servers.net.",
		IPv4: []net.IP{net.ParseIP("198.41.0.4")},
		IPv6: []net.IP{net.ParseIP("2001:503:ba3e::2:30")},
	}

	t.Run("IPv4 only", func(t *testing.T) {
		ips := rs.AllIPs(false)
		if len(ips) != 1 {
			t.Fatalf("expected 1 IP, got %d", len(ips))
		}
		if !ips[0].Equal(net.ParseIP("198.41.0.4")) {
			t.Errorf("got %v, want 198.41.0.4", ips[0])
		}
	})

	t.Run("IPv4 and IPv6", func(t *testing.T) {
		ips := rs.AllIPs(true)
		if len(ips) != 2 {
			t.Fatalf("expected 2 IPs, got %d", len(ips))
		}
	})

	t.Run("no addresses", func(t *testing.T) {
		empty := RootServer{Name: "empty.root-servers.net."}
		ips := empty.AllIPs(false)
		if len(ips) != 0 {
			t.Errorf("expected 0 IPs, got %d", len(ips))
		}
	})
}

func TestDefaultRootDiscoveryConfig(t *testing.T) {
	cfg := DefaultRootDiscoveryConfig()
	if cfg.AllRoots {
		t.Error("AllRoots should be false by default")
	}
	if cfg.IncludeAAAA {
		t.Error("IncludeAAAA should be false by default")
	}
	if cfg.Server != "" {
		t.Error("Server should be empty by default")
	}
}

func TestNormalizeServerName(t *testing.T) {
	tests := []struct {
		input string
		want  string
	}{
		{"a.root-servers.net.", "a.root-servers.net"},
		{"A.ROOT-SERVERS.NET.", "a.root-servers.net"},
		{"b.root-servers.net", "b.root-servers.net"},
		{"root-servers.net.", "root-servers.net"},
	}

	for _, tt := range tests {
		t.Run(tt.input, func(t *testing.T) {
			got := normalizeServerName(tt.input)
			if got != tt.want {
				t.Errorf("normalizeServerName(%q) = %q, want %q", tt.input, got, tt.want)
			}
		})
	}
}

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

	t.Run("NS records", func(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 := extractNSRecords(rrs)
		if len(names) != 2 {
			t.Fatalf("expected 2 names, got %d", len(names))
		}
		if names[0] != "a.root-servers.net." {
			t.Errorf("got %q, want a.root-servers.net.", names[0])
		}
	})

	t.Run("dedup", func(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: "a.root-servers.net."},
		}
		names := extractNSRecords(rrs)
		if len(names) != 1 {
			t.Errorf("expected 1 deduped name, got %d", len(names))
		}

	})
}

func TestExtractIPsFromAnswer(t *testing.T) {
	t.Run("empty", func(t *testing.T) {
		ips := extractIPsFromAnswer(nil, dns.TypeA)
		if len(ips) != 0 {
			t.Errorf("expected 0 IPs, got %d", len(ips))
		}
	})

	t.Run("A records", func(t *testing.T) {
		rrs := []dns.RR{
			&dns.A{Hdr: dns.RR_Header{Rrtype: dns.TypeA}, A: net.ParseIP("198.41.0.4")},
			&dns.A{Hdr: dns.RR_Header{Rrtype: dns.TypeA}, A: net.ParseIP("199.9.14.201")},
		}
		ips := extractIPsFromAnswer(rrs, dns.TypeA)
		if len(ips) != 2 {
			t.Fatalf("expected 2 IPs, got %d", len(ips))
		}
	})

	t.Run("AAAA records", func(t *testing.T) {
		rrs := []dns.RR{
			&dns.AAAA{Hdr: dns.RR_Header{Rrtype: dns.TypeAAAA}, AAAA: net.ParseIP("2001:503:ba3e::2:30")},
		}
		ips := extractIPsFromAnswer(rrs, dns.TypeAAAA)
		if len(ips) != 1 {
			t.Fatalf("expected 1 IP, got %d", len(ips))
		}
	})

	t.Run("filter by type", func(t *testing.T) {
		rrs := []dns.RR{
			&dns.A{Hdr: dns.RR_Header{Rrtype: dns.TypeA}, A: net.ParseIP("198.41.0.4")},
			&dns.AAAA{Hdr: dns.RR_Header{Rrtype: dns.TypeAAAA}, AAAA: net.ParseIP("2001:503:ba3e::2:30")},
		}
		ips := extractIPsFromAnswer(rrs, dns.TypeA)
		if len(ips) != 1 {
			t.Fatalf("expected 1 A IP, got %d", len(ips))
		}
	})
}

func TestDiscoverRootsOverride(t *testing.T) {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	cfg := &RootDiscoveryConfig{
		Server:      "a.root-servers.net",
		IncludeAAAA: false,
	}

	servers, err := DiscoverRoots(ctx, cfg)
	if err != nil {
		t.Logf("skipping (no resolver available): %v", err)
		t.Skip()
	}
	if len(servers) == 0 {
		t.Fatal("expected at least one root server")
	}
	if len(servers[0].IPv4) == 0 {
		t.Error("expected IPv4 addresses for a.root-servers.net")
	}
}

func TestDiscoverRootsSingle(t *testing.T) {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	servers, err := DiscoverRoots(ctx, nil)
	if err != nil {
		t.Logf("skipping (no resolver available): %v", err)
		t.Skip()
	}
	if len(servers) == 0 {
		t.Fatal("expected at least one root server")
	}
	if servers[0].Name == "" {
		t.Error("root server name should not be empty")
	}
}

func TestDiscoverRootsNilConfig(t *testing.T) {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	servers, err := DiscoverRoots(ctx, nil)
	if err != nil {
		t.Logf("skipping (no resolver available): %v", err)
		t.Skip()
	}
	if len(servers) == 0 {
		t.Fatal("expected at least one root server with nil config")
	}
}

func TestBuildNSResponse(t *testing.T) {
	msg := new(dns.Msg)
	msg.SetReply(new(dns.Msg))
	msg.Answer = append(msg.Answer,
		&dns.NS{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS, Class: dns.ClassINET}, Ns: "a.root-servers.net."},
		&dns.NS{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS, Class: dns.ClassINET}, Ns: "b.root-servers.net."},
		&dns.NS{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS, Class: dns.ClassINET}, Ns: "c.root-servers.net."},
	)

	names := extractNSRecords(msg.Answer)
	if len(names) != 3 {
		t.Fatalf("expected 3 NS records, got %d", len(names))
	}

	for _, name := range names {
		if len(name) == 0 || name[len(name)-1] != '.' {
			t.Errorf("expected FQDN, got %q", name)
		}
	}
}

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("extractNSNames: expected 2 names, got %d", len(names))
}
}

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

func TestExtractNSNamesNonNS(t *testing.T) {
rrs := []dns.RR{
&dns.A{Hdr: dns.RR_Header{Name: "a.root-servers.net.", Rrtype: dns.TypeA}, A: net.ParseIP("198.41.0.4")},
}
names := extractNSNames(rrs)
if len(names) != 0 {
t.Errorf("extractNSNames with A records: expected 0 names, got %d", len(names))
}
}

func TestDiscoverRootsAllRoots(t *testing.T) {
ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
defer cancel()

cfg := &RootDiscoveryConfig{
AllRoots:    true,
IncludeAAAA: false,
}

servers, err := DiscoverRoots(ctx, cfg)
if err != nil {
t.Logf("skipping (no resolver available): %v", err)
t.Skip()
}
if len(servers) == 0 {
t.Fatal("expected root servers with AllRoots=true")
}
t.Logf("discovered %d root servers", len(servers))
}

func TestDiscoverRootsAllRootsIncludeAAAA(t *testing.T) {
ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
defer cancel()

cfg := &RootDiscoveryConfig{
AllRoots:    true,
IncludeAAAA: true,
}

servers, err := DiscoverRoots(ctx, cfg)
if err != nil {
t.Logf("skipping (no resolver available): %v", err)
t.Skip()
}
if len(servers) == 0 {
t.Fatal("expected root servers")
}
}

// startMockDNSServer starts a UDP DNS server on a random port that serves
// pre-configured responses. It returns the server address and a stop function.
func startMockDNSServer(t *testing.T, handlerFn dns.HandlerFunc) string {
t.Helper()

mux := dns.NewServeMux()
mux.HandleFunc(".", handlerFn)

srv := &dns.Server{
Addr:    "127.0.0.1:0",
Net:     "udp",
Handler: mux,
}

started := make(chan struct{})
srv.NotifyStartedFunc = func() { close(started) }

go func() {
if err := srv.ListenAndServe(); err != nil && t.Failed() {
return
}
}()

select {
case <-started:
case <-time.After(2 * time.Second):
t.Fatal("mock DNS server did not start in time")
}

// Retrieve the actual bound address from the server's PacketConn.
addr := srv.PacketConn.LocalAddr().String()
t.Cleanup(func() { _ = srv.Shutdown() })
return addr
}

func TestQueryResolverSuccess(t *testing.T) {
	addr := startMockDNSServer(t, func(w dns.ResponseWriter, r *dns.Msg) {
		m := new(dns.Msg)
		m.SetReply(r)
		m.Answer = append(m.Answer,
			&dns.NS{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS, Class: dns.ClassINET, Ttl: 300}, Ns: "a.root-servers.net."},
		)
		_ = w.WriteMsg(m)
	})

	// queryResolver uses 5ns timeout without deadline; provide one
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()
	msg, err := queryResolver(ctx, addr, ".", dns.TypeNS)
	if err != nil {
		t.Fatalf("queryResolver: %v", err)
	}
	names := extractNSRecords(msg.Answer)
	if len(names) == 0 {
		t.Fatal("expected NS records in answer")
	}
}

func TestQueryResolverError(t *testing.T) {
ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
defer cancel()
// Use an address nothing is listening on
_, err := queryResolver(ctx, "127.0.0.1:19999", ".", dns.TypeNS)
if err == nil {
t.Fatal("expected error for unreachable resolver")
}
}

func TestDiscoverSingleRootWithMock(t *testing.T) {
	addr := startMockDNSServer(t, func(w dns.ResponseWriter, r *dns.Msg) {
		m := new(dns.Msg)
		m.SetReply(r)
		q := r.Question[0]
		switch q.Qtype {
		case dns.TypeNS:
			m.Answer = append(m.Answer,
				&dns.NS{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS, Class: dns.ClassINET, Ttl: 300}, Ns: "mock.root-servers.test."},
			)
		case dns.TypeA:
			m.Answer = append(m.Answer,
				&dns.A{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 300}, A: net.ParseIP("127.0.0.1")},
			)
		}
		_ = w.WriteMsg(m)
	})

	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()
	msg, err := queryResolver(ctx, addr, ".", dns.TypeNS)
	if err != nil {
		t.Fatalf("queryResolver: %v", err)
	}
	names := extractNSRecords(msg.Answer)
	if len(names) == 0 {
		names = extractNSNames(msg.Ns)
	}
	if len(names) == 0 {
		t.Skip("mock NS query returned no NS records")
	}
	t.Logf("found %d root NS names from mock: %v", len(names), names)
}

func TestDiscoverAllRootsWithMockServer(t *testing.T) {
	addr := startMockDNSServer(t, func(w dns.ResponseWriter, r *dns.Msg) {
		m := new(dns.Msg)
		m.SetReply(r)
		q := r.Question[0]
		switch q.Qtype {
		case dns.TypeNS:
			m.Answer = append(m.Answer,
				&dns.NS{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS, Class: dns.ClassINET, Ttl: 300}, Ns: "a.mock-roots.test."},
				&dns.NS{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS, Class: dns.ClassINET, Ttl: 300}, Ns: "b.mock-roots.test."},
			)
		case dns.TypeA:
			m.Answer = append(m.Answer,
				&dns.A{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 300}, A: net.ParseIP("127.0.0.1")},
			)
		}
		_ = w.WriteMsg(m)
	})

	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	msg, err := queryResolver(ctx, addr, ".", dns.TypeNS)
	if err != nil {
		t.Fatalf("queryResolver: %v", err)
	}
	names := extractNSRecords(msg.Answer)
	if len(names) < 2 {
		t.Fatalf("expected 2 NS names, got %d", len(names))
	}

	// Also cover AAAA path
	aaaaMsg, err := queryResolver(ctx, addr, "a.mock-roots.test.", dns.TypeAAAA)
	if err != nil {
		t.Logf("AAAA query error (acceptable): %v", err)
	} else {
		t.Logf("AAAA query returned %d answers", len(aaaaMsg.Answer))
	}
}

func TestMinTTLFromMsgWithExtraRecords(t *testing.T) {
msg := new(dns.Msg)
msg.Answer = append(msg.Answer, &dns.A{
Hdr: dns.RR_Header{Ttl: 300},
A:   net.ParseIP("1.2.3.4"),
})
// Extra record (non-OPT) with smaller TTL
msg.Extra = append(msg.Extra, &dns.NS{
Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeNS, Ttl: 60},
Ns:  "a.root-servers.net.",
})

ttl := minTTLFromMsg(msg)
if ttl != 60*time.Second {
t.Errorf("minTTLFromMsg = %v, want 60s", ttl)
}
}

func TestMinTTLFromMsgOPTIgnored(t *testing.T) {
msg := new(dns.Msg)
msg.Answer = append(msg.Answer, &dns.A{
Hdr: dns.RR_Header{Ttl: 300},
A:   net.ParseIP("1.2.3.4"),
})
// OPT record should be ignored
msg.Extra = append(msg.Extra, &dns.OPT{
Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeOPT},
})

ttl := minTTLFromMsg(msg)
if ttl != 300*time.Second {
t.Errorf("minTTLFromMsg with OPT = %v, want 300s", ttl)
}
}