#define _POSIX_C_SOURCE 200809L

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
  FILE * cur_in_file;
  int i; char c;

  int using_unbuffered_output = 0;

  int error_occurred = 0;

  /*
    Check for -u and use unbuffered output if present
  */
  while((c = getopt(argc, argv, "u")) != -1) {
    if(c == 'u') {
      using_unbuffered_output = 1;
    }
  }

  /*
    Set unbuffered output. We do this for both stdin and stdout, let setvbuf
    allocate the buffer (that we don't need), _IONBF tells it to not buffer,
    and we just say 15 character buffer because, well, eh, who cares?
  */
  if(using_unbuffered_output) {
    setvbuf(stdin, NULL, _IONBF, 15);
    setvbuf(stdout, NULL, _IONBF, 15);
  }

  /*
    If no input files were given, just open up stdin
  */
  if(argc == 1 || optind == argc) {
    cur_in_file = stdin;
    for(c = fgetc(cur_in_file); c != EOF; c = fgetc(cur_in_file)) {
	    fprintf(stdout, "%c", c);
    }
    fclose(cur_in_file);
  }
  
  /*
    Open up each file given (or stdin if - was given), print it to stdout,
    then close it and move to the next while there are still files
  */
  for(i = optind; i < argc; i++) {
    if(argv[i][0] == '-' && argv[i][1] == '\0') {
      cur_in_file = stdin;
    }
    else {
      cur_in_file = fopen(argv[i], "r");
      if(cur_in_file == NULL) {
	      fprintf(stderr, "%s: %s: No such file or directory\n", argv[0], argv[i]);
	      error_occurred = 1;
      }
    }
    for(c = fgetc(cur_in_file); c != EOF; c = fgetc(cur_in_file)) {
	    fprintf(stdout, "%c", c);
    }
    fclose(cur_in_file);
  }

  if(error_occurred) {
    return 1;
  }
  else {
    return 0;
  }
}