package conn

import (
"bytes"
"net"
"os"
"time"
)

const (
ICMP_ECHO_REQUEST = 8
ICMP_ECHO_REPLY   = 0
)

// Ping Request
func makePingRequest(id, seq, pktlen int, filler []byte) []byte {
p := make([]byte, pktlen)
copy(p[8:], bytes.Repeat(filler, (pktlen-8)/len(filler)+1))

p[0] = ICMP_ECHO_REQUEST // type
p[1] = 0                 // code
p[2] = 0                 // cksum
p[3] = 0                 // cksum
p[4] = uint8(id >> 8)    // id
p[5] = uint8(id & 0xff)  // id
p[6] = uint8(seq >> 8)   // sequence
p[7] = uint8(seq & 0xff) // sequence

// calculate icmp checksum
cklen := len(p)
s := uint32(0)
for i := 0; i < (cklen - 1); i += 2 {
s += uint32(p[i+1])<<8 | uint32(p[i])
}
if cklen&1 == 1 {
s += uint32(p[cklen-1])
}
s = (s >> 16) + (s & 0xffff)
s = s + (s >> 16)

// place checksum back in header; using ^= avoids the
// assumption the checksum bytes are zero
p[2] ^= uint8(^s & 0xff)
p[3] ^= uint8(^s >> 8)

return p
}

func parsePingReply(p []byte) (id, seq int) {
id = int(p[4])<<8 | int(p[5])
seq = int(p[6])<<8 | int(p[7])
return
}

// Ping
func Ping(addr string, i int) bool {

// *IPAddr
raddr, e := net.ResolveIPAddr("ip4", addr)
if e != nil {
return false
}

// *IPConn
ipconn, ee := net.DialIP("ip4:icmp", nil, raddr)
if ee != nil {
return false
}

// 保证连接正常关闭
defer ipconn.Close()

// PID
sendid := os.Getpid() & 0xffff
sendseq := 1
pingpktlen := 64

for {

sendpkt := makePingRequest(sendid, sendseq, pingpktlen, []byte("Go Ping"))

// 发送请求
n, err := ipconn.WriteToIP(sendpkt, raddr)
if err != nil || n != pingpktlen {
break
}

// 超时
ipconn.SetDeadline(time.Now().Add(5 * time.Second))

// 返回数据
resp := make([]byte, 1024)
for {

// 读取返回
_, _, err := ipconn.ReadFrom(resp)
if err != nil {
break
}

// 判断状态
if resp[0] != ICMP_ECHO_REPLY {
continue
}

// 判断状态
rcvid, rcvseq := parsePingReply(resp)
if rcvid != sendid || rcvseq != sendseq {
break
}

// 成功返回
return true

}

// 执行次数内未成功返回
if i == sendseq {
break
}

// 计数器
sendseq++

}

// 失败返回
return false
}