package main

import (
	"flag"
	"fmt"
	"net"
	"os"
	"strconv"
	"time"
)

func main() {
	var count int
	var timeout int64
	var size int
	var neverstop bool

	flag.Int64Var(&timeout,"w",1000,"等待每次回复的超时时间(毫秒)。")
	flag.IntVar(&count,"n",4,"要发送的回显请求数。")
	flag.IntVar(&size,"l",32,"要发送缓冲区大小。")
	flag.BoolVar(&neverstop,"t",false,"Ping 指定的主机，直到停止。")

	flag.Parse()
	args := flag.Args()

	if len(args) < 1 {
		fmt.Println("Usage: ",os.Args[0],"host")
		flag.PrintDefaults()
		flag.Usage()
		os.Exit(1)
	}

	ch := make(chan int)
	argsmap := map[string]interface{}{}

	argsmap["w"] = timeout
	argsmap["n"] = count
	argsmap["l"] = size
	argsmap["t"] = neverstop

	for _,host := range args {
		go ping(host,ch,argsmap)
	}

	for i := 0; i < len(args); i++ {
		<-ch
	}

	os.Exit(0)
}

func ping(host string,c chan int,args map[string]interface{}) {
	var count int
	var size int
	var timeout int64
	var neverstop bool
	count = args["n"].(int)
	size = args["l"].(int)
	timeout = args["w"].(int64)
	neverstop = args["t"].(bool)

	cname,_ := net.LookupCNAME(host)
	starttime := time.Now()
	conn,err := net.DialTimeout("ip4:icmp",host,time.Duration(timeout*1000*1000))
	ip := conn.RemoteAddr()
	fmt.Println("正在 Ping " + cname + " [" + ip.String() + "] 具有 32 字节的数据:")

	var seq int16 = 1
	id0,id1 := genidentifier(host)
	const ECHO_REQUEST_HEAD_LEN = 8

	sendN := 0
	recvN := 0
	lostN := 0
	shortT := -1
	longT := -1
	sumT := 0

	for count > 0 || neverstop {
		sendN++
		var msg []byte = make([]byte,size+ECHO_REQUEST_HEAD_LEN)
		msg[0] = 8                        // echo
		msg[1] = 0                        // code 0
		msg[2] = 0                        // checksum
		msg[3] = 0                        // checksum
		msg[4],msg[5] = id0,id1         //identifier[0] identifier[1]
		msg[6],msg[7] = gensequence(seq) //sequence[0],sequence[1]

		length := size + ECHO_REQUEST_HEAD_LEN

		check := checkSum(msg[0:length])
		msg[2] = byte(check >> 8)
		msg[3] = byte(check & 255)

		conn,err = net.DialTimeout("ip:icmp",time.Duration(timeout*1000*1000))

		checkError(err)

		starttime = time.Now()
		conn.SetDeadline(starttime.Add(time.Duration(timeout * 1000 * 1000)))
		_,err = conn.Write(msg[0:length])

		const ECHO_REPLY_HEAD_LEN = 20

		var receive []byte = make([]byte,ECHO_REPLY_HEAD_LEN+length)
		n,err := conn.Read(receive)
		_ = n

		var endduration int = int(int64(time.Since(starttime)) / (1000 * 1000))

		sumT += endduration

		time.Sleep(1000 * 1000 * 1000)

		if err != nil || receive[ECHO_REPLY_HEAD_LEN+4] != msg[4] || receive[ECHO_REPLY_HEAD_LEN+5] != msg[5] || receive[ECHO_REPLY_HEAD_LEN+6] != msg[6] || receive[ECHO_REPLY_HEAD_LEN+7] != msg[7] || endduration >= int(timeout) || receive[ECHO_REPLY_HEAD_LEN] == 11 {
			lostN++
			fmt.Println("对 " + cname + "[" + ip.String() + "]" + " 的请求超时。")
		} else {
			if shortT == -1 {
				shortT = endduration
			} else if shortT > endduration {
				shortT = endduration
			}
			if longT == -1 {
				longT = endduration
			} else if longT < endduration {
				longT = endduration
			}
			recvN++
			ttl := int(receive[8])
			//			fmt.Println(ttl)
			fmt.Println("来自 " + cname + "[" + ip.String() + "]" + " 的回复: 字节=32 时间=" + strconv.Itoa(endduration) + "ms TTL=" + strconv.Itoa(ttl))
		}

		seq++
		count--
	}
	stat(ip.String(),sendN,lostN,recvN,shortT,longT,sumT)
	c <- 1
}

func checkSum(msg []byte) uint16 {
	sum := 0

	length := len(msg)
	for i := 0; i < length-1; i += 2 {
		sum += int(msg[i])*256 + int(msg[i+1])
	}
	if length%2 == 1 {
		sum += int(msg[length-1]) * 256 // notice here,why *256?
	}

	sum = (sum >> 16) + (sum & 0xffff)
	sum += (sum >> 16)
	var answer uint16 = uint16(^sum)
	return answer
}

func checkError(err error) {
	if err != nil {
		fmt.Fprintf(os.Stderr,"Fatal error: %s",err.Error())
		os.Exit(1)
	}
}

func gensequence(v int16) (byte,byte) {
	ret1 := byte(v >> 8)
	ret2 := byte(v & 255)
	return ret1,ret2
}

func genidentifier(host string) (byte,byte) {
	return host[0],host[1]
}

func stat(ip string,sendN int,lostN int,recvN int,shortT int,longT int,sumT int) {
	fmt.Println()
	fmt.Println(ip," 的 Ping 统计信息:")
	fmt.Printf("    数据包: 已发送 = %d，已接收 = %d，丢失 = %d (%d%% 丢失)，\n",int(lostN*100/sendN))
	fmt.Println("往返行程的估计时间(以毫秒为单位):")
	if recvN != 0 {
		fmt.Printf("    最短 = %dms，最长 = %dms，平均 = %dms\n",sumT/sendN)
	}
}