#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>
#include <netinet/in.h>

#define MAX_BUFFER 128
#define TIME_SERVER_PORT 37

void myTime(int connectionFd, struct sockaddr_in servers[], unsigned int sizeOfServers)
{
	int in;
	time_t czas;
	struct sockaddr_in echoOdpAdr;
	unsigned int odpDl;
	int unknown = 1;
	int i;

	odpDl = sizeof(echoOdpAdr);
	in = recvfrom(connectionFd, &czas, sizeof(time_t), 0, (struct sockaddr *) &echoOdpAdr, &odpDl);
	for (i = 0; i < sizeOfServers; ++i)
	{
		if (servers[i].sin_addr.s_addr == echoOdpAdr.sin_addr.s_addr) unknown = 0;
	}
	if (unknown == 1)
	{
		fprintf(stderr,"Blad: pakiet z nieznanego zrodla.\n");
		exit(1);
	}
	if (in != sizeof(time_t))
	{
		printf("blad read()\n");
		exit(1);
	}
	czas = ntohl(czas) - 2208988800UL;
	printf("Otrzymano odpowiedz z serwera: %s:%i.\n", inet_ntoa(echoOdpAdr.sin_addr), ntohs(echoOdpAdr.sin_port));
	printf("Czas na serwerze: %s", ctime(&czas));
}

int main (int argc, char *argv[] )
{
	int connectionFd;
	int i;
	unsigned int sizeOfServers = 2;
	struct sockaddr_in servers[2];
	unsigned sockaddrInSize = sizeof(struct sockaddr_in);

	if (argc != 5) {
		fprintf(stderr,"Usage: %s IP1 PORT1 IP2 PORT2\n",
		        argv[0]);
		exit(1);
	}

	memset(&servers[0], 0, sockaddrInSize);
	memset(&servers[1], 0, sockaddrInSize);
	servers[0].sin_port=htons(atoi(argv[2]));
	servers[1].sin_port=htons(atoi(argv[4]));
	servers[0].sin_family = AF_INET;
	servers[1].sin_family = AF_INET;
	servers[0].sin_addr.s_addr = inet_addr(argv[1]);
	servers[1].sin_addr.s_addr = inet_addr(argv[3]);

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

	for (i = 0; i < sizeOfServers; ++i)
	{
		errno = (int)NULL;
		if (sendto(connectionFd , NULL, 0, 0, (struct sockaddr *) &servers[i], sockaddrInSize) == -1)
		{
			perror("cant sendto()...");
			fprintf(stderr, "... to %s:%i", inet_ntoa(servers[i].sin_addr), ntohs(servers[i].sin_port));
			return(1);
		}
	}

	myTime(connectionFd, servers, sizeOfServers);
	return(0);
}