/********* STUDENTS WRITE THE NEXT SEVEN ROUTINES *********/

#include "Stud.h"

#define SIZE 20
#define TIMEOUT 20

int A_SEQ;
int B_SEQ;
int FLAG = 0;
int ACK_FLAG = 0;

struct pkt backup;

int add_sum(struct pkt packet){
    int checksum = packet.seqnum + packet.acknum;
    for(int i = 0; i < SIZE; i++)
        checksum += packet.payload[i];
    return checksum;
}

int error(char AorB, struct pkt packet)
{
  if(AorB == 'A')
  {
    if(packet.acknum != A_SEQ)
    {
      printf("A Fel ack: %d\n", packet.seqnum);
      return 0;
    }
    else if(packet.checksum != add_sum(packet))
    {
      printf("A corrupted: %s\n", packet.payload);
      return 0;
    }
  }
  else
  {
    if(packet.seqnum != B_SEQ || packet.checksum != add_sum(packet))
    {
      packet.acknum = 1 - B_SEQ;
      packet.checksum = add_sum(packet);
      printf("B corrupted: %s\n", packet.payload);
      tolayer3(1, packet);
      return 0;
    }

  }
  return 1;
}

/* called from layer 5, passed the data to be sent to other side */
void A_output(struct msg message)
{
  if(ACK_FLAG || FLAG)
  {
    printf("Not yet acked dropping message %s \n",message.data);
    return;
  }


  struct pkt packet;
  packet.seqnum = A_SEQ;
  memmove(packet.payload, message.data, SIZE);
  packet.checksum = add_sum(packet);
  backup = packet;

  ACK_FLAG = 1;
  FLAG = 1;
  printf("A output %s\n", packet.payload);
  tolayer3(0, packet);
  starttimer(0, TIMEOUT);

}

/* called from layer 3, when a packet arrives for layer 4 */
void A_input(struct pkt packet)
{
  printf("A input acked: %s\n", packet.payload);
  if(!error('A', packet))
    return;
  stoptimer(0);
  FLAG = 0;

  A_SEQ = 1 - A_SEQ;
  B_SEQ = 1 - B_SEQ;
  ACK_FLAG = 0;
}

/* called when A's timer goes off */
void A_timerinterrupt()
{
  printf("Timerinterrupt: %s\n",backup.payload);
  tolayer3(0, backup);
  starttimer(0, TIMEOUT);
}

/* the following routine will be called once (only) before any other */
/* entity A routines are called. You can use it to do any initialization */
void A_init()
{
  A_SEQ = 0;
  FLAG = 0;
}

/* Note that with simplex transfer from a-to-B, there is no B_output() */

/* called from layer 3, when a packet arrives for layer 4 at B*/
void B_input(struct pkt packet)
{

  if(!error('B', packet))
    return;
  packet.acknum = B_SEQ;
  packet.checksum = add_sum(packet);
  printf("B input %s\n",packet.payload);
  tolayer3(1, packet);
  tolayer5(1, packet.payload);

}
/* the following rouytine will be called once (only) before any other */
/* entity B routines are called. You can use it to do any initialization */
void B_init()
{
  B_SEQ = 0;
}

/* called when B's timer goes off */
void B_timerinterrupt()
{}
void B_output(struct msg message)  /* need be completed only for extra credit */
{}