package netresolve

import (
	"context"
	"errors"
	"net"
	"net/netip"
	"sync/atomic"
	"testing"
	"time"
)

type lookupFunc func(context.Context, string, string) ([]netip.Addr, error)

func (f lookupFunc) LookupNetIP(ctx context.Context, network, host string) ([]netip.Addr, error) {
	return f(ctx, network, host)
}

func TestDNSOutageFallbackAndReturnToSystem(t *testing.T) {
	t.Parallel()
	var healthy atomic.Bool
	var fallbacks atomic.Int32
	r := &Resolver{timeout: time.Second}
	r.system = lookupFunc(func(_ context.Context, network, host string) ([]netip.Addr, error) {
		if network != "ip4" || host != "api.ipify.org" {
			t.Errorf("unexpected query %s %s", network, host)
		}
		if healthy.Load() {
			return []netip.Addr{netip.MustParseAddr("1.0.0.1")}, nil
		}
		return nil, &net.DNSError{Err: "server misbehaving", IsTemporary: true}
	})
	r.fallbacks = []lookup{lookupFunc(func(_ context.Context, network, host string) ([]netip.Addr, error) {
		fallbacks.Add(1)
		if network != "ip4" || host != "api.ipify.org." {
			t.Errorf("fallback must use absolute family-specific query: %s %s", network, host)
		}
		return []netip.Addr{netip.MustParseAddr("1.1.1.1")}, nil
	})}
	for _, recovered := range []bool{false, true} {
		healthy.Store(recovered)
		ips, err := r.LookupNetIP(context.Background(), "ip4", "api.ipify.org")
		want := "1.1.1.1"
		if recovered {
			want = "1.0.0.1"
		}
		if err != nil || len(ips) != 1 || ips[0].String() != want {
			t.Fatalf("DNS recovery: %v %v", ips, err)
		}
	}
	if fallbacks.Load() != 1 {
		t.Fatal("system recovery did not stop fallback use")
	}
}

func TestSlowDNSCannotBlockWorkingFallback(t *testing.T) {
	t.Parallel()
	slow := lookupFunc(func(ctx context.Context, _, _ string) ([]netip.Addr, error) { <-ctx.Done(); return nil, ctx.Err() })
	r := &Resolver{system: slow, timeout: 20 * time.Millisecond, fallbacks: []lookup{slow, lookupFunc(func(context.Context, string, string) ([]netip.Addr, error) {
		return []netip.Addr{netip.MustParseAddr("1.1.1.1")}, nil
	})}}
	started := time.Now()
	ips, err := r.LookupNetIP(context.Background(), "ip4", "api.ipify.org")
	if err != nil || len(ips) != 1 || time.Since(started) > time.Second {
		t.Fatalf("blocked fallback: %v %v", ips, err)
	}
	r.fallbacks = []lookup{slow}
	if _, err = r.LookupNetIP(context.Background(), "ip4", "api.ipify.org"); err == nil {
		t.Fatal("total outage was hidden")
	}
}

func TestDNSFallbackDoesNotOverrideNegativeAnswersOrLocalNames(t *testing.T) {
	t.Parallel()
	for _, test := range []struct {
		host string
		err  error
	}{
		{"api.ipify.org", &net.DNSError{IsNotFound: true}},
		{"api.ipify.org", errors.New("permanent DNS error")},
		{"pi.hole", &net.DNSError{IsTemporary: true}},
		{"private.example", &net.DNSError{IsTemporary: true}},
	} {
		r := &Resolver{timeout: time.Second, system: lookupFunc(func(context.Context, string, string) ([]netip.Addr, error) { return nil, test.err }), fallbacks: []lookup{lookupFunc(func(context.Context, string, string) ([]netip.Addr, error) {
			t.Error("unexpected external query")
			return nil, nil
		})}}
		if _, err := r.LookupNetIP(context.Background(), "ip4", test.host); !errors.Is(err, test.err) {
			t.Fatalf("original error lost: %v", err)
		}
	}
}

func TestCanceledDNSDoesNotStartFallback(t *testing.T) {
	t.Parallel()
	ctx, cancel := context.WithCancel(context.Background())
	cancel()
	r := &Resolver{timeout: time.Second, system: lookupFunc(func(ctx context.Context, _, _ string) ([]netip.Addr, error) { return nil, ctx.Err() }), fallbacks: []lookup{lookupFunc(func(context.Context, string, string) ([]netip.Addr, error) {
		t.Error("fallback after cancellation")
		return nil, nil
	})}}
	if _, err := r.LookupNetIP(ctx, "ip6", "api6.ipify.org"); !errors.Is(err, context.Canceled) {
		t.Fatal(err)
	}
}

func TestDialAddressesTriesNextAddress(t *testing.T) {
	t.Parallel()
	listener, err := net.Listen("tcp4", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err)
	}
	defer listener.Close()
	_, port, _ := net.SplitHostPort(listener.Addr().String())
	conn, err := DialAddresses(context.Background(), "tcp4", []netip.Addr{netip.MustParseAddr("127.0.0.2"), netip.MustParseAddr("127.0.0.1")}, port)
	if err != nil {
		t.Fatal(err)
	}
	conn.Close()
}