#include <ctype.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int main(int argc, char **argv) {
  if (argc != 2) {
    fprintf(stderr, "Wrong argument count!\n");
    return 1;
  }

  int src = open(argv[1], O_RDONLY);
  if (src == -1) {
    perror("Opening the source file failed");
    return 1;
  }

  char *filename_buffer = malloc(strlen(argv[1]) + 3);

  sprintf(filename_buffer, "%s_l", argv[1]);
  int lower = open(filename_buffer, O_WRONLY | O_CREAT | O_TRUNC, 0644);
  if (lower == -1)
    perror("Creating the lowercase variant failed");

  sprintf(filename_buffer, "%s_u", argv[1]);
  int upper = open(filename_buffer, O_WRONLY | O_CREAT | O_TRUNC, 0644);
  if (upper == -1)
    perror("Creating the uppercase variant failed");

  free(filename_buffer);

  if (lower == -1 && upper == -1) {
    close(src);
    return 1;
  }

  char buf[256];
  while (1) {
    int cnt = read(src, buf, 256);
    if (cnt <= 0)
      break;

    for (int i = 0; i < cnt; ++i)
      buf[i] = tolower(buf[i]);
    write(lower, buf, cnt);

    for (int i = 0; i < cnt; ++i)
      buf[i] = toupper(buf[i]);
    write(upper, buf, cnt);
  }
  close(src);
  close(lower);
  close(upper);
  return 0;
}