package linkwatch

import (
	"encoding/binary"
	"testing"

	"golang.org/x/sys/unix"
)

// msg is a netlink message of a type, with a payload of n bytes.
func msg(typ uint16, n int) []byte {
	b := make([]byte, unix.NLMSG_HDRLEN+n)
	binary.NativeEndian.PutUint32(b[0:4], uint32(len(b)))
	binary.NativeEndian.PutUint16(b[4:6], typ)
	return b
}

func TestLinks(t *testing.T) {
	for _, c := range []struct {
		name string
		b    []byte
		want bool
	}{
		{"a new link", msg(unix.RTM_NEWLINK, 16), true},
		{"a link going", msg(unix.RTM_DELLINK, 16), true},
		{"an address", msg(unix.RTM_NEWADDR, 16), false},
		{"a link after an address (padded)", append(msg(unix.RTM_NEWADDR, 13), append(make([]byte, 3), msg(unix.RTM_NEWLINK, 8)...)...), true},
		{"truncated", msg(unix.RTM_NEWLINK, 16)[:10], false},
		{"a length beyond the datagram", msg(unix.RTM_NEWLINK, 16)[:unix.NLMSG_HDRLEN+4], false},
		{"empty", nil, false},
	} {
		if got := links(c.b); got != c.want {
			t.Errorf("%s: %v", c.name, got)
		}
	}
}