#include <sys/types.h> /* for open, lseek */
#include <sys/stat.h>  /* for open */
#include <fcntl.h>     /* for open */
#include <stdio.h>     /* for fprintf etc  */
#include <stdlib.h>    /* for exit */
#include <unistd.h>    /* for open, lseek */

#include "mem.h"

int init_shared_file(int *fd, char *file, size_t size){
  *fd = open(file, O_RDWR | O_CREAT | O_EXCL, S_IRWXU);
  if(*fd < 0){
    fprintf(stderr, "The file: %s exists -- opening it and checking size\n", file);
    return open_shared_file(fd, file, size);
  } else {
    fprintf(stderr, "The file: %s doesn't exist -- creating it\n", file);
    if(lseek(*fd, size - 1, SEEK_SET) == -1){
      perror("lseek error!");
      return -1;
    }
    if(write(*fd, "", 1) != 1){
      perror("write error!");
      return -1;
    }
  }
  return 0;
}

int open_shared_file(int *fd, char *file, size_t size){
  struct stat statbuf;
  *fd = open(file, O_RDWR, S_IRWXU);
    if(*fd < 0){
      fprintf(stderr, "Couldn't open %s! Exiting\n", file);
      return -1;
    }
    if(fstat(*fd, &statbuf) < 0){
      perror("fstat error!");
      return -1;
    }
    fprintf(stderr, "Checking file size: %s is %ld bytes\n", file, statbuf.st_size);
    if(statbuf.st_size < size){
      if(lseek(*fd, size - 1, SEEK_SET) == -1){
        perror("lseek error!");
  return -1;
      }
      if(write(*fd, "", 1) != 1){
        perror("write error!");
  return -1;
      }
    }
    if(fstat(*fd, &statbuf) < 0){
      perror("fstat error!");
      return -1;
    }
    fprintf(stderr, "The file: %s is now %ld bytes\n", file, statbuf.st_size);
    return 0;
}