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

void failed(int code) {
  fputs("Failed\n", stderr) ;
  exit(code) ;
}

int main(int argc, char *argv[], char *envp[]) {
  uid_t yourID ;
  pid_t ppid ;
  struct passwd *yourPWinfo ;
  char *yourName, *shmIDstr, IDbuff[256] ;
  int shmID ;
  void *shmAddr ;

  yourID = getuid() ;
  if ((yourPWinfo = getpwuid(yourID)) == NULL) {
    fprintf(stdout, "Unable to find PW entry for %d\n", yourID) ;
    exit(1) ;
  }
  yourName = yourPWinfo->pw_name ;
  ppid = getppid() ;

  fprintf(stdout, "Called by process %d run by %s\n", ppid, yourName) ;

  if (strcmp(argv[1], "csci331"))
    failed(101) ;

  if (getenv("CLASS") == NULL)
    failed(102) ;

  if (strcmp(getenv("CLASS"), "csci331"))
    failed(103) ;

  if ((shmIDstr=getenv("SHMID")) == NULL)
    failed(104) ;

  shmID = 0 ;
  while (*shmIDstr) {
    if (('0' <= *shmIDstr) && (*shmIDstr <= '9'))
      shmID = 10*shmID + *shmIDstr - '0' ;
    else
      failed(105) ;
    ++shmIDstr ;
  }

  if ((shmAddr = shmat(shmID, (void *)NULL, 0)) == (void *)-1)
    failed(106) ;

  if (((int *)shmAddr)[0] != yourID)
    failed(107) ;

  if (((int *)shmAddr)[1] != ppid)
    failed(108) ;

  sprintf(IDbuff, "I am %s at %d", yourName, ppid) ;
  fprintf(stdout, "%s\n", IDbuff) ;

  if (strcmp((char *)(((int *)shmAddr)+2), IDbuff))
    failed(109) ;

  exit(0) ;
}