//go:build linux

package tcp

import (
	"context"
	"errors"
	"fmt"
	"net/netip"
	"testing"
	"time"

	"github.com/qdm12/gluetun/internal/command"
	"github.com/qdm12/gluetun/internal/firewall"
	"github.com/qdm12/gluetun/internal/netlink"
	"github.com/qdm12/gluetun/internal/pmtud/constants"
	"github.com/qdm12/gluetun/internal/pmtud/ip"
	"github.com/qdm12/gluetun/internal/routing"
	"github.com/qdm12/log"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"golang.org/x/sys/unix"
)

func Test_runTest(t *testing.T) {
	t.Parallel()

	localNonListenPort := reserveClosedPort(t)

	noopLogger := &noopLogger{}

	cmder := command.New()
	fw, err := firewall.NewConfig(t.Context(), noopLogger, cmder, nil, nil)
	if errors.Is(err, firewall.ErrIPTablesNotSupported) {
		t.Skip("iptables not installed, skipping TCP PMTUD tests")
	}
	require.NoError(t, err, "creating firewall config")

	netlinker := netlink.New(noopLogger)
	loopbackMTU, err := findLoopbackMTU(netlinker)
	require.NoError(t, err, "finding loopback IPv4 MTU")
	defaultIPv4MTU, err := findDefaultIPv4RouteMTU(netlinker)
	require.NoError(t, err, "finding default IPv4 route MTU")

	ctx, cancel := context.WithCancel(t.Context())

	const family = constants.AF_INET
	const excludeMark = 4545
	fd, stop, err := startRawSocket(family, excludeMark)
	require.NoError(t, err)

	const ipv4 = true
	tracker := newTracker(fd, ipv4)
	trackerCh := make(chan error)
	go func() {
		trackerCh <- tracker.listen(ctx)
	}()

	// Our local ethernet MTU could be 1500, and the server could advertise
	// an MSS of 1400, but the real link to the server could have an MTU of 1300,
	// so we need to adjust our test so it passes. We are not actually path MTU
	// discovering here, just testing that we can receive the expected TCP packets
	// for a given MTU.
	const mtuSafetyBuffer = 200

	t.Cleanup(func() {
		stop()
		cancel() // stop listening
		err = <-trackerCh
		require.NoError(t, err)
	})

	testCases := map[string]struct {
		timeout time.Duration
		server  netip.AddrPort
		mtu     uint32
		success bool
	}{
		"local_not_listening": {
			timeout: time.Hour,
			server:  netip.AddrPortFrom(netip.AddrFrom4([4]byte{127, 0, 0, 1}), localNonListenPort),
			mtu:     loopbackMTU,
			success: true,
		},
		"remote_not_listening": {
			timeout: 50 * time.Millisecond,
			server:  netip.AddrPortFrom(netip.AddrFrom4([4]byte{1, 1, 1, 1}), 12345),
			mtu:     defaultIPv4MTU - mtuSafetyBuffer,
		},
		"1.1.1.1:443": {
			timeout: 5 * time.Second,
			server:  netip.AddrPortFrom(netip.AddrFrom4([4]byte{1, 1, 1, 1}), 443),
			mtu:     defaultIPv4MTU - mtuSafetyBuffer,
			success: true,
		},
		"1.1.1.1:80": {
			timeout: 5 * time.Second,
			server:  netip.AddrPortFrom(netip.AddrFrom4([4]byte{1, 1, 1, 1}), 80),
			mtu:     defaultIPv4MTU - mtuSafetyBuffer,
			success: true,
		},
		"8.8.8.8:443": {
			timeout: 5 * time.Second,
			server:  netip.AddrPortFrom(netip.AddrFrom4([4]byte{8, 8, 8, 8}), 443),
			mtu:     defaultIPv4MTU - mtuSafetyBuffer,
			success: true,
		},
	}

	for name, testCase := range testCases {
		t.Run(name, func(t *testing.T) {
			t.Parallel()

			dst := testCase.server

			const proto = constants.IPPROTO_TCP
			src, cleanup, err := ip.SrcAddr(dst, proto)
			require.NoError(t, err, "getting source address to reach remote server %s", dst)
			t.Cleanup(cleanup)

			revert, err := fw.TempDropOutputTCPRST(t.Context(), src, dst, excludeMark)
			require.NoError(t, err)
			t.Cleanup(func() {
				err := revert(context.Background())
				assert.NoError(t, err)
			})

			ctx, cancel := context.WithTimeout(t.Context(), testCase.timeout)
			defer cancel()
			err = runTest(ctx, dst, testCase.mtu, excludeMark,
				fd, tracker, fw, noopLogger)
			if testCase.success {
				require.NoError(t, err)
			} else {
				require.Error(t, err)
			}
		})
	}
}

var errRouteNotFound = errors.New("route not found")

func findLoopbackMTU(netlinker *netlink.NetLink) (mtu uint32, err error) {
	routes, err := netlinker.RouteList(netlink.FamilyV4)
	if err != nil {
		return 0, fmt.Errorf("getting routes list: %w", err)
	}
	for _, route := range routes {
		if route.Dst.IsValid() && route.Dst.Addr().IsLoopback() {
			link, err := netlinker.LinkByIndex(route.LinkIndex)
			if err != nil {
				return 0, fmt.Errorf("getting link by index: %w", err)
			}
			// Quirk: make sure it is maximum 65535, and not i.e. 65536
			// or the IP header 16 bits will fail to fit that packet length value.
			const maxMTU = 65535
			return min(link.MTU, maxMTU), nil
		}
	}
	return 0, fmt.Errorf("%w: no loopback route found", errRouteNotFound)
}

func findDefaultIPv4RouteMTU(netlinker *netlink.NetLink) (mtu uint32, err error) {
	noopLogger := &noopLogger{}
	routing := routing.New(netlinker, noopLogger)
	defaultRoutes, err := routing.DefaultRoutes()
	if err != nil {
		return 0, fmt.Errorf("getting default routes: %w", err)
	}
	for _, route := range defaultRoutes {
		if route.Family != netlink.FamilyV4 {
			continue
		}
		link, err := netlinker.LinkByName(defaultRoutes[0].NetInterface)
		if err != nil {
			return 0, fmt.Errorf("getting link by name: %w", err)
		}
		return link.MTU, nil
	}
	return 0, fmt.Errorf("%w: no default route found", errRouteNotFound)
}

func reserveClosedPort(t *testing.T) (port uint16) {
	t.Helper()

	fd, err := unix.Socket(constants.AF_INET, constants.SOCK_STREAM, constants.IPPROTO_TCP)
	require.NoError(t, err)
	t.Cleanup(func() {
		err := unix.Close(fd)
		assert.NoError(t, err)
	})

	addr := &unix.SockaddrInet4{
		Port: 0,
		Addr: [4]byte{127, 0, 0, 1},
	}

	err = unix.Bind(fd, addr)
	if err != nil {
		_ = unix.Close(fd)
		t.Fatal(err)
	}

	sockAddr, err := unix.Getsockname(fd)
	if err != nil {
		_ = unix.Close(fd)
		t.Fatal(err)
	}

	sockAddr4, ok := sockAddr.(*unix.SockaddrInet4)
	if !ok {
		_ = unix.Close(fd)
		t.Fatal("not an IPv4 address")
	}

	return uint16(sockAddr4.Port) //nolint:gosec
}

type noopLogger struct{}

func (l *noopLogger) Patch(_ ...log.Option)     {}
func (l *noopLogger) Debug(_ string)            {}
func (l *noopLogger) Debugf(_ string, _ ...any) {}
func (l *noopLogger) Info(_ string)             {}
func (l *noopLogger) Warn(_ string)             {}
func (l *noopLogger) Warnf(_ string, _ ...any)  {}
func (l *noopLogger) Error(_ string)            {}