package icmp

import (
	"bytes"
	"encoding/binary"
	"net"
	"time"

	"golang.org/x/net/icmp"
)

func netAddrToIPAddr(a net.Addr) *net.IPAddr {
	switch v := a.(type) {
	case *net.UDPAddr:
		return &net.IPAddr{IP: v.IP, Zone: v.Zone}
	case *net.IPAddr:
		return v
	}
	return nil
}

func (pkt *Packet) BuildEchoRequestMessage(icmptype Type) ([]byte, error) {
	if pkt.Nbytes < 48 {
		pkt.Nbytes = 48
	}
	if pkt.Nbytes > 8192 {
		pkt.Nbytes = 8192
	}
	bs := bytes.Repeat([]byte{1}, pkt.Nbytes-8)
	pkt.SendTime = time.Now()
	binary.BigEndian.PutUint64(bs, uint64(pkt.SendTime.UnixNano()))
	binary.BigEndian.PutUint64(bs[8:], uint64(pkt.Seq))
	binary.BigEndian.PutUint64(bs[16:], uint64(pkt.ID))
	copy(bs[24:], pkt.UUID[:])

	body := &icmp.Echo{
		ID:   pkt.ID % 65536,  // 2 bytes
		Seq:  pkt.Seq % 65536, // 2 bytes
		Data: bs,
	}

	msg := &icmp.Message{
		Type: icmptype, // 1 byte
		Code: 0,        // 1 byte, Checksum 2 bytes
		Body: body,
	}

	msgBytes, err := msg.Marshal(nil)
	if err != nil {
		return nil, err
	}
	return msgBytes, nil
}