#include <iostream>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <unistd.h>
#include <string.h>

#define BUFSIZE 1024

using namespace std;

/* Funkce checksum je opsaná z p&#345;íslu&#261;ných RFC dokument&#367;. */
unsigned short checksum(unsigned char *addr, int count)
{
  register long sum = 0;
  
  while( count > 1 )  
  {
    /*  This is the inner loop */
    sum += * ((unsigned short *) addr)++;
    count -= 2;
  }  
  /*  Add left-over byte, if any */
  if( count > 0 )
    sum += * (unsigned char *) addr;
  /*  Fold 32-bit sum to 16 bits */
  while (sum>>16)
    sum = (sum & 0xffff) + (sum >> 16);
  return ~sum;
}


int main(int argc, char *argv[])
{
  size_t size;
  hostent *host; 
  icmphdr *icmp, *icmpRecv;
  iphdr *ip;
  int sock, lenght;
  unsigned int ttl;
  sockaddr_in sendSockAddr, receiveSockAddr;
  char buffer[BUFSIZE];
  fd_set mySet;
  timeval tv;
  char *addrString;
  unsigned short int pid = getpid(), p;

  if (argc != 2)
  {
    cerr << "Syntaxe:\n\t" << argv[0]
	 << " " << "adresa" << endl;
    return -1;
  }
  /* Zjistíme info o vzdáleném po&#269;íta&#269;i */
  if ((host = gethostbyname(argv[1])) == NULL)
  {
    cerr << "©patná adresa" << endl;
    return -1;
  }
  /* Vytvo&#345;ím soket */
  if ((sock = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1)
  {
    cerr << "Nelze vytvo&#345;it soket" << endl;
    return -1;
  }
  setsockopt(sock, SOL_IP, IP_TTL, (const char *)&ttl, sizeof(ttl));
  /* Zaplníme polo&#318;ky ICMP hlavi&#269;ky */
  icmp = (icmphdr *)malloc(sizeof(icmphdr));
  icmp->type = ICMP_ECHO;
  icmp->code = 0;
  icmp->un.echo.id = pid;
  /* P&#345;ipravíme sendto */
  sendSockAddr.sin_family = AF_INET;
  sendSockAddr.sin_port = 0;
  memcpy(&(sendSockAddr.sin_addr), host->h_addr, host->h_length);
  for (p = 1; p <= 5; p++)
  {
    icmp->checksum = 0;
    icmp->un.echo.sequence = p;
    icmp->checksum = checksum((unsigned char *)icmp, sizeof(icmphdr));
    sendto(sock, (char *)icmp, sizeof(icmphdr), 0, (sockaddr *)&sendSockAddr, sizeof(sockaddr));
    tv.tv_sec = 5;
    tv.tv_usec = 0;
    do
    {
      FD_ZERO(&mySet);
      FD_SET(sock, &mySet);
      if (select(sock + 1, &mySet, NULL, NULL, &tv) < 0)
      {
	cerr << "Selhal select" << endl;
	break;
      }
      if (FD_ISSET(sock, &mySet))
      {
	size = sizeof(sockaddr_in);
	if ((lenght = recvfrom(sock, buffer, BUFSIZE, 0, (sockaddr *)&receiveSockAddr, &size)) == -1)
	{
	  cerr << "Problem p&#345;i p&#345;ijímáni dat" << endl;
	}
	/* P&#345;i&#261;el blok dat IP hlavi&#269;ka + ICMP hlavi&#269;ka. */ 
	ip = (iphdr *) buffer;
	icmpRecv = (icmphdr *) (buffer + ip->ihl * 4);
	if ((icmpRecv->un.echo.id == pid) && (icmpRecv->type == ICMP_ECHOREPLY) && (icmpRecv->un.echo.sequence == p))
	{
	  addrString = strdup(inet_ntoa(receiveSockAddr.sin_addr));
	  host = gethostbyaddr(&receiveSockAddr.sin_addr, 4, AF_INET);
	  cout << lenght << " byt&#367; z " << (host == NULL? "?" : host->h_name) << " (" << addrString << "): icmp_seq=" << icmpRecv->un.echo.sequence << " ttl=" << (int)ip->ttl << " &#269;as=nevím, nem&#283;&#345;il jsem:-)" << endl;
	  free(addrString);
	}
      }
      else
      {
	cout << "&#268;as vypr&#261;el" << endl;
	break;
      }
    } while (!((icmpRecv->un.echo.id == pid) && (icmpRecv->type == ICMP_ECHOREPLY) && (icmpRecv->un.echo.sequence == p)));
  }
  close(sock);
  free(icmp);
  return 0;
}