#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>

#ifdef WIN32
#include <windows.h>
#else 
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#endif

#define BUFSZ 512
#define MULTICAST_PORT  7766
#define MULTICAST_GROUP "239.0.0.1"
 
#define RECEIVE_IP_ADDR "128.127.58.113"
#define TRANSMIT_IP_ADDR "128.127.58.112"

#define USE_RECV_ADDR

/**
 * socket creation function.
 * this function will create a multicast socket for reading or writing.
 * @param[out] sock: structure sockaddr_in used in recv/sendto functions
 * @param[in] type: type of socket: 'r' for reading, 'w' for writing
 * @return a opened socket. Exit program on error (exit() called)
 */
int socket_init(struct sockaddr_in *sock, char type)
{
  struct ip_mreq imr;
  int sd;
  unsigned char ttl = 1;
  struct in_addr If;
 
  /* create socket */
  sd = socket(PF_INET, SOCK_DGRAM, 0);
  if (sd < 0)
  {
    perror("socket");
    exit(EXIT_FAILURE);
  }

  /* initialize sock descriptor */
  memset(sock, 0, sizeof(struct sockaddr_in));

	switch (type)
	{
		case 'r':
			/* receive mode */
			sock->sin_family = AF_INET;
			sock->sin_port = htons(MULTICAST_PORT);
#ifdef USE_RECV_ADDR
			sock->sin_addr.s_addr = inet_addr(RECEIVE_IP_ADDR);
#else
			sock->sin_addr.s_addr = htonl(INADDR_ANY);
#endif
			if (bind(sd, (struct sockaddr *) sock, sizeof(struct sockaddr_in)) < 0)
			{
				perror("bind");
				exit(1);
			}

			If.s_addr = inet_addr(RECEIVE_IP_ADDR);

			if(setsockopt(sd, IPPROTO_IP, IP_MULTICAST_IF, (char*)&If,  sizeof(If)))
			{
				perror("IP_MULTICAST_IF");
				exit(1);
			}

			/* multicast group to join */
			imr.imr_multiaddr.s_addr = inet_addr(MULTICAST_GROUP);
			/* interface to read on */
			imr.imr_interface.s_addr = inet_addr(RECEIVE_IP_ADDR);
 
			/* set GROUP option */
			if (setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (void *) &imr, sizeof(struct ip_mreq)) < 0)
			{
				perror("setsockopt: IP_ADD_MEMBERSHIP");
				exit(1);
			}
 
			/* enable multicast */
			if (0 != setsockopt(sd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl)))
			{
				perror("setsockopt");
				exit(1);
			}
			break;
		case 'w':
			/* transmission mode */
			sock->sin_family = AF_INET;
			sock->sin_port = 0;
			sock->sin_addr.s_addr = inet_addr(TRANSMIT_IP_ADDR);
			if (bind(sd, (struct sockaddr *) sock, sizeof(struct sockaddr_in)) < 0)
			{
				perror("bind");
				exit(1);
			}

			sock->sin_family = AF_INET;
			sock->sin_port = htons(MULTICAST_PORT);
			sock->sin_addr.s_addr = inet_addr(MULTICAST_GROUP);
        
			/* enable multicast */
			if (setsockopt(sd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl)) == -1)
			{
				perror("setsockopt: IP_MULTICAST_TTL");
				exit(EXIT_FAILURE);
			}
			break;
		default:
			printf("socket_init: unknown type /%c/\n", type);
			exit(EXIT_FAILURE);
	}

	return sd;
}
 
 
void m_receive(void)
{
  struct sockaddr_in from;
  unsigned int len = sizeof(from);
  /* create the reception socket */
  int sd = socket_init(&from, 'r');
  int cnt;
  char buf[BUFSZ];
  /* infinite loop */
  while (1)
  {/* try to receive from socket */
    cnt = recvfrom(sd, buf, sizeof(buf), 0, (struct sockaddr *) &from, &len);
    if (cnt < 0)
	  {/* something bad happened, quit */
      perror("recvfrom");
      exit(1);
    }
	  else if (cnt == 0)
	  {/* socket closed (udp should never goes here) exit while loop */
      break;
    }
    /* all goes right, write the received message */
    buf[cnt] = 0;
    printf("%s\n", buf);
  }
  printf("m_receive: done\n");
}

/**
 * transmission function.
 * @param buf: message to send.
 */
void m_send(const char *buf)
{
  struct sockaddr_in to;
  /* create the transmission socket */
  int sd = socket_init(&to, 'w');
  int cnt;

  /* send the message (just like we whoumd have done with regular socket */
  cnt = sendto(sd, buf, strlen(buf), 0, (struct sockaddr *) &to, sizeof(to));
  if (cnt < 0)
  {
    perror("sendto");
    exit(1);
  } 
}
 
 
/** usage : 
 *      cmd.exe r
 *      cmd.exe w message  
 */
void usage(const char *name)
{
    printf("usage :\n\n");
    printf("reception mode\n");
    printf("\t %s r\n\n", name);
    printf("transmission mode\n");
    printf("\t %s w message to send\n", name);
}
 
/**
 * Application entry point
 */
int main(int argc, char **argv)
{
#ifdef WIN32
    WSADATA wsaData;
    int ret = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (ret != 0)
	{
        printf("WSAStartup failed: %d\n", ret);
        return 1;
    }
#endif
 
 
    if (argc < 2)
	{
        usage(*argv);
    }
	else
	{
		switch (*argv[1])
		{
			case 'r':
				/* go in receive mode */
				m_receive();
				break;
			case 'w':
				/* note that this method is not optimized : we create a socket of each word of the message to send. */
				{
					int i;
					for (i = 2; i != argc; ++i)
					{/* send each parameter given to program*/
						m_send(argv[i]);
					}
				}
				break;
			default:
				usage(*argv);
				break;
		}
	}
#ifdef WIN32
    WSACleanup();
#endif

    return 0;
}