#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <time.h>

#define MAX_BUFFER 128
#define TIME_SERVER_PORT 37

void myTime(int connectionFd, struct sockaddr_in * echoSerwAdr)
{
	int in;
	time_t czas;
	struct sockaddr_in echoOdpAdr;
	unsigned int odpDl;
	int i = 0;

	odpDl = sizeof(echoOdpAdr);
	errno = (int)NULL;
	while (1)
	{
		in = recvfrom(connectionFd, &czas, sizeof(time_t), MSG_DONTWAIT, (struct sockaddr *) &echoOdpAdr, &odpDl);
		if (in == -1)
		{
			if (errno == EAGAIN)
			{
				i++;
				if (i == 5)
				{
					fprintf(stderr, "Timeout. No response from server.\n");
					exit(1);
				}
				sleep(1);
				continue;
			} else {
				perror("recvfrom()");
				exit(1);
			}
		} else {
			if (in != sizeof(time_t))
			{
				printf("blad recvfrom()\n");
				exit(1);
			}
			break;
		}
	}

	if (echoSerwAdr->sin_addr.s_addr != echoOdpAdr.sin_addr.s_addr)
	{
		fprintf(stderr,"Blad: pakiet z nieznanego zrodla.\n");
		exit(1);
	}
	
	czas = ntohl(czas) - 2208988800UL;
	printf("Czas pobrany z serwera: %s", ctime(&czas));
}

int main (int argc, char *argv[] )
{
	int connectionFd;
	int port;
	struct sockaddr_in servaddr;

	if ((argc < 2) || (argc > 3)) {
		fprintf(stderr,"Usage: %s <Server IP> [<Time Port>]\n",
		        argv[0]);
		exit(1);
	}

	if (argc == 3)
		port=atoi(argv[2]);
	else
		port=TIME_SERVER_PORT;

	errno = (int)NULL;
	connectionFd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
	if (connectionFd == -1)
	{
		perror("socket() error");
		exit(1);
	}

	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(port);

	servaddr.sin_addr.s_addr = inet_addr(argv[1]);

	errno = (int)NULL;
	if (sendto(connectionFd , NULL, 0, 0,(struct sockaddr*) &servaddr,sizeof(servaddr)) == -1)
	{
		perror("cant sendto() server");
	} else {
		myTime(connectionFd, &servaddr);
	}

	return(0);
}