#include <stdio.h>     /* for fprintf  */
#include <stdlib.h>    /* for exit     */
#include <unistd.h>    /* for fork     */
#include <string.h>    /* for strtok   */
#define BUFFSIZE 50
int parse_args(int argc,  char *argv[ ], int *np){
  if ( (argc != 2) || ((*np = atoi (argv[1])) <= 0) ) {
    fprintf (stderr, "Usage: %s nprocs\n", argv[0]);
    return(-1); };
  return(0); 
}
int make_trivial_ring(){   
  int   fd[2];
  if (pipe (fd) == -1) 
    return(-1); 
  if ((dup2(fd[0], STDIN_FILENO) == -1) ||
      (dup2(fd[1], STDOUT_FILENO) == -1)) 
    return(-2); 
  if ((close(fd[0]) == -1) || (close(fd[1]) == -1))   
    return(-3); 
  return(0); 
}
int add_new_node(int *pid){
  int fd[2];
  if (pipe(fd) == -1) 
    return(-1); 
  if ((*pid = fork()) == -1)
    return(-2); 
  if(*pid > 0 && dup2(fd[1], STDOUT_FILENO) < 0)
    return(-3); 
  if (*pid == 0 && dup2(fd[0], STDIN_FILENO) < 0)
    return(-4); 
  if ((close(fd[0]) == -1) || (close(fd[1]) == -1)) 
    return(-5);
  return(0);
}
void get_integers(char buff[], long *first, long *second){
  char* token = NULL;
  if((first == NULL) || (second == NULL)) return;
  if(read(STDIN_FILENO, buff, BUFFSIZE) > 0){
    *first  = atol((((token = strtok(buff," ")) == NULL) ? "0" : token));
    *second = atol((((token = strtok(NULL," ")) == NULL) ? "0" : token)); 
  } else {
    *first = 0;
    *second = 0;
  }
}
void safe_sum(long first, long *second, long *third){
  if((second == NULL) || third == NULL) return;
  *third = first + *second;
  if(*third < 0){
    fprintf(stderr, 
            "Overflow detected: %ld + %ld != %ld\n",
            first, *second, *third);
    *third   = 0;
    *second  = 0; };
}
int send_numbers(char buff[], long num1, long num2){
  int bytes, len;
  sprintf(buff, "%ld %ld", num1, num2);
  len = strlen(buff) + 1;
  if((bytes = write(STDOUT_FILENO, buff, len)) != len){
    fprintf(stderr, 
            "Write of %d bytes failed, only sent %d bytes\n",
            len, bytes);
    return -1; 
  } else {
    return bytes;
  }
}

void report_sum(int i, long first, long old_second, long second, long third){
  fprintf(stderr,
          "\nProcess %d with PID %d and parent PID %d recieved %ld %ld and sent %ld %ld.\n",
          i, (int)getpid(), (int)getppid(), first, old_second, second, third); 
}
int main(int argc,  char *argv[]){
   int    i;               /* number of this process (starting with 1)   */
   int    childpid;        /* indicates process should spawn another     */ 
   int    nprocs;          /* total number of processes in ring          */ 
   char   buff[BUFFSIZE];  /* string for integers                        */
   long   first;           /* first integer in fibonacci computation     */
   long   second;          /* second integer in fibonacci computation    */
   long   third ;          /* sum of first and second                    */
   if(parse_args(argc,argv,&nprocs) < 0) exit(EXIT_FAILURE);
   if(make_trivial_ring() < 0){
     perror("Could not make trivial ring");
     exit(EXIT_FAILURE); };
   for (i = 1; i < nprocs;  i++) {
     if(add_new_node(&childpid) < 0){
       perror("Could not add new node to ring");
       exit(EXIT_FAILURE); };
     if (childpid) break; };
   {
     /* ring process code  */     
     long old_second;
     if(i == 1){
       /* mother of all processes */
       send_numbers(buff, 1,1); }
     /* all processes     */
     get_integers(buff, &first, &second);
     old_second = second;
     safe_sum(first,&second,&third);
     if(i > 1){ 
       send_numbers(buff, second, third);
       report_sum( i, first, old_second, second, third); }
     else {
       fprintf(stderr,"\n\nfibonacci(%d) = %ld\n\n", nprocs, second); }
     exit(EXIT_SUCCESS); 
   }
}     /* end of main program here */