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:
		if ip := v.IP.To4(); ip != nil {
			return ip
		}
	case *net.IPAddr:
		if ip := v.IP.To4(); ip != nil {
			return ip
		}
	}
	return nil
}

func BuildEchoRequestMessage(id, seq, size int, icmptype Type) ([]byte, error) {
	if size < 24 {
		size = 24
	}
	bs := bytes.Repeat([]byte{1}, size)
	binary.BigEndian.PutUint64(bs, uint64(time.Now().UnixNano()))
	binary.BigEndian.PutUint64(bs[8:], uint64(seq))
	binary.BigEndian.PutUint64(bs[16:], uint64(id))

	body := &icmp.Echo{
		ID:   id % 65535,
		Seq:  seq % 65536,
		Data: bs,
	}

	msg := &icmp.Message{
		Type: icmptype,
		Code: 0,
		Body: body,
	}

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