//-------------------------------------------------------------------
//	utcdemo.cpp
//
//	This example shows how we can obtain the current time from
//	an official U.S. government time-server, based on RFC-868,
//	and then show the time-of-day using Pacific Daylight Time. 
//	In this program we will employ the UDP transport-protocol.
//
//	     compile using:  $ g++ utcdemo.cpp -o utcdemo
//	     execute using:  $ ./utcdemo
//
//	programmer: ALLAN CRUSE
//	written on: 12 APR 2009
//-------------------------------------------------------------------

#include <netdb.h>	// for gethostbyname()
#include <stdio.h>	// for printf(), perror() 
#include <stdlib.h>	// for exit() 
#include <string.h>	// for strcpy()
#include <arpa/inet.h>	// for inet_ntoa()

#define TIME_PORT	37

char servername[] = "time-nw.nist.gov";

int main( int argc, char **argv )
{
	struct hostent	*pp = gethostbyname( servername );
	if ( !pp ) { herror( "gethostbyname" ); exit(1); } 
	char	peeraddr[ 16 ] = { 0 };
	strcpy( peeraddr, inet_ntoa( *(in_addr*)pp->h_addr ) );
	printf( "\nTime-server is \'%s\' (%s) \n", servername, peeraddr );

	struct sockaddr_in	saddr = { 0 };
	socklen_t		salen = sizeof( saddr );
	saddr.sin_family 	= AF_INET;
	saddr.sin_port		= htons( TIME_PORT );
	saddr.sin_addr.s_addr	= inet_addr( peeraddr );

	int	sock = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );
	if ( sock < 0 ) { perror( "socket" ); exit(1); }

	int	tx = sendto( sock, "", 0, 0, (sockaddr*)&saddr, salen );
	if ( tx < 0 ) { perror( "sendto" ); exit(1); }

	unsigned int	since = 0;
	int	rx = recvfrom( sock, &since, 4, 0, (sockaddr*)&saddr, &salen );
	if ( rx < 0 ) { perror( "recvfrom" ); exit(1); }
	unsigned int	seconds_since_1900 = htonl( since );

	// display the Coordinated Universal Time in hh:mm:ss format
	unsigned int	ss = seconds_since_1900 % 60;
	unsigned int	mm = ( seconds_since_1900 / 60 ) % 60;
	unsigned int	hh = ( seconds_since_1900 / 3600 ) % 24;
	printf( "\nseconds_since_1900: %u \n", seconds_since_1900 );
	printf( "\nTime now is %02d:%02d:%02d (GMT) \n", hh, mm, ss ); 

	// display the current Pacific Daylight Time in hh:mm:ss format
	seconds_since_1900 -= (7 * 3600);
	ss = seconds_since_1900 % 60;
	mm = ( seconds_since_1900 / 60 ) % 60;
	hh = ( seconds_since_1900 / 3600 ) % 24;
	printf( "\nTime now is %02d:%02d:%02d (PDT) \n", hh, mm, ss ); 
	printf( "\n" );
}