/* alternating bit receiver for internet datagram demo */
/* modification 9/20/93 with Louis Sanchez's bug fix */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.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: abreceiver -[d] c2host c2portno\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[])
{
	int sock; 
	struct sockaddr_in from;
	struct sockaddr_in to;
	struct sockaddr_in C2addr;
	struct hostent *hp;

	int n;
	int state=1;
	struct Msg m;
	char AltBit;
	int c;
	extern char *optarg;
	extern int   optind;
	int option_exist = 0;

	int counter = 0;
	int length;
	int debug = 1;
	char *C2Host;  /* channel C2's host name */
	int C2PortNo;

   /* process command line args */
    while ((c=getopt(argc,argv,"d")) != EOF)
    {
        option_exist = 1;
        switch(c)
        {
        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);
        }
    }

	C2Host = argv[optind++];
	C2PortNo = atoi(argv[optind++]);

	printf("C2hostname=%s, C2PortNo=%d\n", C2Host, C2PortNo);
	/* create socket from which to read */
	sock = socket(AF_INET, SOCK_DGRAM, 0);
	if (sock < 0) {
		perror("opening datagram socket");
		exit(1);
	}
	/* create name structure with wildcard using INADDR_ANY */
	from.sin_family = AF_INET;
	from.sin_addr.s_addr = INADDR_ANY;
	from.sin_port = 0;  
	/* port no. < 1024 IPPORT_RESERVED is for privillege process */
	/* here just initialized it, it will be assigned value after call */
	/* getsockname() */
	if (bind(sock, (struct sockaddr_in *)&from, sizeof(struct sockaddr_in))) {
		perror("binding name to datagram socket");
		exit(1);
	}
	length = sizeof(from);
	if (getsockname(sock, (struct sockaddr_in *)&from, (socklen_t *)&length)) {
		perror("getting socket name");
		exit(1);
	}
	/* Find assigned port value and print out. */
	printf("socket has port #%d\n", ntohs(from.sin_port));

    hp = gethostbyname(C2Host);
    if (hp == 0) {
        fprintf(stderr, "%s: unknown host", C2Host);
        exit(2);
    }
    bcopy(hp->h_addr, &C2addr.sin_addr, hp->h_length);
    /* in system V unix use memcpy */
    /* memcpy(&C2addr.sin_addr, hp->h_addr, hp->h_length); */
    C2addr.sin_family = AF_INET;
    C2addr.sin_port = htons(C2PortNo);

    AltBit = 0; //##
	 
	 while (1) {
	 printf("\nState%d: ", state);
	 switch(state) {
	 case 1: 
		      if(recv(sock, &m, sizeof(m), 0) < 0)
		            perror("receiving datagram message");
		      printf("Received +D%d msg=%s", m.alternating_bit, m.buf);
		      if (AltBit != m.alternating_bit) {
					printf(" It is dupliate or error!");
		         state = 8; 
				} else state = 2;
				break;

	 case 2: printf("Deliver data=%s\n", m.buf); 
	         state= 3;
				break;


	 case 3:	
		      bcopy(&m.src, &to, sizeof(to));
		      bcopy(&m.dst, &m.src, sizeof(to));
		      bcopy(&to, &m.dst, sizeof(to));
		      m.msgtype = ACK;
		      printf("Sending A0");
		      if (sendto(sock, &m, sizeof(m), 0, 
				    (struct sockaddr_in *)&C2addr, sizeof(C2addr)) < 0)
			      perror("send ACK message");
		      AltBit = !AltBit; //##
				state = 4;
				break;

	 case 4: 
		      if(recv(sock, &m, sizeof(m), 0) < 0)
		            perror("receiving datagram message");
		      printf("Received +D%d msg=%s", m.alternating_bit, m.buf);
		      if (AltBit != m.alternating_bit) {
					printf(" It is dupliate or error!");
		         state = 7; 
				} else state = 5;
				break;

	 case 5: printf("Deliver data=%s\n", m.buf); 
	         state= 6;
				break;


	 case 6:	
		      bcopy(&m.src, &to, sizeof(to));
		      bcopy(&m.dst, &m.src, sizeof(to));
		      bcopy(&to, &m.dst, sizeof(to));
		      m.msgtype = ACK;
		      printf("Sending -A1");
		      if (sendto(sock, &m, sizeof(m), 0, 
				    (struct sockaddr_in *)&C2addr, sizeof(C2addr)) < 0)
			      perror("send ACK message");
		      AltBit = !AltBit; //##
				state = 1;
				break;

	 case 7: 
		bcopy(&m.src, &to, sizeof(to));
		bcopy(&m.dst, &m.src, sizeof(to));
		bcopy(&to, &m.dst, sizeof(to));
		m.msgtype = ACK;
		m.alternating_bit = 0; //##

		printf("Resending -A0");
		if (sendto(sock, &m, sizeof(m), 0, 
		    (struct sockaddr_in *)&C2addr, sizeof(C2addr)) < 0)
			perror("send ACK message");
			state = 4;
      break;

	 case 8: 
		bcopy(&m.src, &to, sizeof(to));
		bcopy(&m.dst, &m.src, sizeof(to));
		bcopy(&to, &m.dst, sizeof(to));
		m.msgtype = ACK;
		m.alternating_bit = 1; //##

		printf("Resending -A1");
		if (sendto(sock, &m, sizeof(m), 0, 
		    (struct sockaddr_in *)&C2addr, sizeof(C2addr)) < 0)
			perror("send ACK message");
			state = 1;
      break;
   } // switch(state)
	} // while
	close(sock);
}