/* alternating bit sender for internet datagram demo */

#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

#define DATA 1
#define ACK  2

struct Msg {
   struct    sockaddr_in dst;
   struct    sockaddr_in src;
   char    msgtype;
   char    buf[80];
   char   alternating_bit; };

void help_msg()
{
   printf("format: absender -[dn] rcvhost rcvportno c1host c1portno\n");
   printf("          option: n set the number of messages to be sent\n");
   printf("          option: d set debug mode\n");
}

void printsockaddr(struct sockaddr_in *arg)
{
    struct hostent *hp;
    printf("  sockaddr_in: ");
    printf("Domain=%d, ", arg->sin_family);
    hp=gethostbyaddr((char*)&(arg->sin_addr), sizeof(arg->sin_addr), AF_INET);
    printf("Hostname=%s, ", hp->h_name);
    printf("Port=%d, ", ntohs(arg->sin_port));
    printf("Address=%s,\n", inet_ntoa(arg->sin_addr));
}


main(int argc, char *argv[])
{
   extern char *optarg;
   extern int   optind;
   int option_exist = 0;
   int c;
   int debug = 1;

   char *rcvHost;  /* receiver's host name */
   int rcvPortNo;
   char *C1Host;  /* channel C1's host name */
   int C1PortNo;
   struct Msg mto;
   struct sockaddr_in c1addr;
   struct sockaddr_in from;
   struct hostent *hp;


   char hostname[80];
   int i;
   int noOfPackets;
   int state = 1;

   /* process command line args */
   while ((c=getopt(argc,argv,"dn:")) != EOF)
   {
      option_exist = 1;
      switch(c)
      {
      case 'n':
         if ((noOfPackets = atoi(optarg)) < 1) noOfPackets = 1;
         printf("The number of messages to be sent is %d\n", noOfPackets);
         break;
      case 'd':
         debug = 1;
         printf("set debug mode on\n");
         break;
      case '?':
         help_msg();
         exit (1);
      default:
         fprintf (stderr, "unrecognized arg >%s<\n", optarg);
         help_msg();
         exit (1);
      }
   }

   rcvHost = argv[optind++];
   rcvPortNo = atoi(argv[optind++]);
   C1Host = argv[optind++];
   C1PortNo = atoi(argv[optind++]);

   /* create socket from which to read packet */

   /* translate the domain name C1Host to its IP address using gethostbyname()
      assign IP address and portno  to a sockaddr_in structure variable, 
      here we use c1addr, for sending msg to C1.
      Make sure you use htons() before assign C1PortNo to sin_port field of
      the sockaddr_in variable */

   /* fill the src field of mto with the sender's IP address and portno 
      we use gethostname() to get current host name, 
      then use gethostbyname to get the IP address.
   */
   gethostname(hostname, sizeof(hostname));
   hp = gethostbyname(hostname);
   if (hp == 0) {
      fprintf(stderr, "%s: unknown host",rcvHost);
      exit(2);
   }
   bcopy(hp->h_addr, &mto.src.sin_addr, hp->h_length);

   /* here I assume from is the struct sockaddr_in variable  we used in 
      bind() after getsockname() we have the assigned port no in 
      from.sin_port.  Here we just copy it over.
   */
   mto.src.sin_family = AF_INET;
   mto.src.sin_port = from.sin_port;
      
   /* fill the dst fiedl of mto with the receiver's IP address and portno
      */
   /* repeat sending for noOfPackets */
   for (i=1; i<noOfPackets; ) {
      /* use the above for loop to relace the while loop
      /* implement sender of alternating bit protocol */
      /* For NewData transition from state 1 to 2, and 4 to 5,
         use 
         sprintf(mto.buf, "packet %d\0", i++);
         to creat the packet content.
      */
      printf("state %d:", state);
      switch (state) {
      case 1:
              sprintf(mto.buf, "packet %d\0", i++);
              printf("Get NewData=%s\n", mto.buf);
              state = 2;
              break;
      case 2:
              printf("send D0 with msg=%s\n", mto.buf);
              /* set mto.alternating_bit and use sendto to send it */
              /* use &c1addr as the fifth parameter in sendto() to send
                 the msg to C1 */
              state = 3;
              break;

      case 3: 
              /* set up readfds */
              /* set up timeout tv variable */
              /* call select() */
              break;
      /* add other states */
      }
   }
}