#define period 20000

#define theserver "80.199.27.122"

#define _GNU_SOURCE 1

#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sched.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>

#include <syslog.h>
#include <sys/poll.h>
#include <linux/ppdev.h>
#include <linux/parport.h>

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <getopt.h>


struct time_shm
{
 int shm_mode;
 int stamp_count;
 time_t clock_sec;
 int clock_usec;
 time_t receive_sec;
 int receive_usec;
 int leap_indicator;
 int precision;
 int number_of_samples;
 int is_valid;
 int place_holder[10];
};

struct time_shm *sh;

struct time_shm *attach_shm(int unit)
{
 int shm_id=0;
 shm_id=shmget(0x4e545030+unit, sizeof(struct time_shm),
  IPC_CREAT|0700);
 if(shm_id==-1) {

     fprintf(stderr,"shmget failed.\n");
     perror("shmget");
     exit(1);
 }
 sh=(struct time_shm *) shmat(shm_id, 0, 0);
 if(sh==(void *) -1 || sh==0) {
     fprintf(stderr,"shmat failed.\n");
     perror("shmat");
     exit(1);
 }
 return sh;
}



void set_shm(unsigned r_sec, unsigned r_usec, unsigned c_sec, unsigned c_usec, unsigned prec)
{
 sh->shm_mode=1;
 sh->leap_indicator=0;
 sh->is_valid=0;
 __asm__ __volatile__("": : :"memory");
 sh->stamp_count++;
 __asm__ __volatile__("": : :"memory");

 sh->precision=prec;
 sh->clock_sec=c_sec;
 sh->clock_usec=c_usec;
 sh->receive_sec=r_sec;
 sh->receive_usec=r_usec;
 __asm__ __volatile__("": : :"memory");
 sh->stamp_count++;
 __asm__ __volatile__("": : :"memory");
 sh->is_valid=1;
 
}







int waitsok(int sok)
{
  struct timeval stTimeOut;
  fd_set stReadFDS;
  FD_ZERO(&stReadFDS);

  // Timeout 3 sec
  stTimeOut.tv_sec = 3;
  stTimeOut.tv_usec = 0;
  FD_SET(sok, &stReadFDS);
  return select(sok+1, &stReadFDS, 0, 0, &stTimeOut);
}





  int sockfd,n;
    struct sockaddr_in servaddr,cliaddr;
      unsigned sendbuf[10];
        unsigned recvbuf[10];
          int dt;
          


struct timeval tv,rtv;
struct timezone tz;




extern int errno;

int main(argc, argv)
     int argc;
     char *argv[];
{
  int i, f, f1, f2, f3, fx, whatitis; 
  int sp_fd = 0, pp_fd = 0, n_fd=0, zoo_poll = 0, hitolow = 0, flap = 0;
  int deviceis_serial = 0,  deviceis_parallel = 0, deviceis_nic=0, bogon = 0;
  int unit = 0;

  int locked=0;
  unsigned int pp_nfds = 1;

  struct pollfd pp_pollfd[2];
  struct ppdev_frob_struct frobit;
  struct sched_param sp;
  struct rlimit rl;

  char *prog;
  char *pps_dev[256];
  char *pps_sig[256];		/* name of sig line: CD RTS DSR */
  int sig = TIOCM_CD;

  prog = argv[0];

  attach_shm(0);

  if (1) {
    if(fork()!=0) return(0);
    setsid();
    setpgrp();
    setsid();
    getrlimit(RLIMIT_NOFILE, &rl);
    for (i = 0; i <= rl.rlim_max; i++)
      (void) close(i);
  }
  
  
  sockfd=socket(AF_INET,SOCK_DGRAM,0);
  bzero(&servaddr,sizeof(servaddr));
  servaddr.sin_family = AF_INET;
  servaddr.sin_addr.s_addr=inet_addr("217.198.219.102");
  servaddr.sin_port=htons(124);
  
  for(;;) {
loopstart:
    gettimeofday(&tv,&tz);      
    usleep(100000); //100 ms for the peer to have updated the table entry for this second
    sendbuf[0]=54656866;
    sendbuf[1]=tv.tv_sec&255;  

    servaddr.sin_port=htons(124);
    servaddr.sin_addr.s_addr=inet_addr("127.0.0.1");
    sendto(sockfd,sendbuf,8,0,(struct sockaddr *)&servaddr,sizeof(servaddr));
rerx2:
    if (waitsok(sockfd)) {
      n=recvfrom(sockfd,recvbuf,40,0,NULL,NULL);
      if (n!=20) goto rerx2;
      if (recvbuf[0]!=54652345) goto rerx2;
      if (recvbuf[1]!=sendbuf[1]) goto rerx2;
//      printf("local arrival time:%i\n",recvbuf[2]);
      dt=-recvbuf[2];
    } else {
//      printf("failed to get local time\n");
      sleep(14);
      goto loopstart;
    }

    servaddr.sin_addr.s_addr=inet_addr(theserver);
    servaddr.sin_port=htons(124);
    sendto(sockfd,sendbuf,8,0,(struct sockaddr *)&servaddr,sizeof(servaddr));
rerx1:
    if (waitsok(sockfd)) {
      n=recvfrom(sockfd,recvbuf,40,0,NULL,NULL);
      if (n!=20) goto rerx1;
      if (recvbuf[0]!=54652345) goto rerx1;
      if (recvbuf[1]!=sendbuf[1]) goto rerx1;
//      printf("remote arrival time: %i\n",recvbuf[2]);
      dt=dt+recvbuf[2];
    } else {
//      printf("failed to get time\n");
      sleep(14);
      goto loopstart;
    }
    /*
     if the remote clock is fast, dt is positive.
    */
    

    //  dt-= 10000; this is the place to compensate if you picked different phases
    
    
    
    dt=((dt+(5*period)+(period/2))%period)-(period/2);
    //printf("delta (positive means that remote clock is ahead):%i\n",dt);

    if ((dt>-4000)&&(dt<4000)) locked=1;
    if (locked) {
      rtv.tv_sec=tv.tv_sec-1;
      rtv.tv_usec=tv.tv_usec+1000000; //pre adjust
      rtv.tv_usec += dt;      
      while (rtv.tv_usec>=1000000) {
        rtv.tv_sec+=1;
        rtv.tv_usec-=1000000;
      }
      set_shm(tv.tv_sec,tv.tv_usec, rtv.tv_sec,rtv.tv_usec, -15); //30 usec precision
    }
    sleep(14);
  }

}