#include <errno.h> /* errno, EBADF, EFAULT, EINVAL, ELOOP, ENAMETOOLONG,
                    * ENOENT, ENOMEM, ENOTDIR, EOVERFLOW */
#include <stdio.h> /* fprintf(3), getc(3), putc(3), setvbuf(3), stderr, stdin,
                    * stdout */
#include <string.h> /* strerror(3) */
#include <sysexits.h> /* EX_DATAERR, EX_NOINPUT, EX_OK, EX_OSERR,
                       * EX_UNAVAILABLE, EX_USAGE */
#include <unistd.h> /* getopt(3) */
#include <sys/stat.h> /* stat(2), struct stat, S_ISDIR */

static char *program_name = "cat";

/* NetBSD's default size according to an strace */
static unsigned char buf[4096];

int main(int argc, char *argv[]){
	char *argv0;
	int c;
	struct stat fi; /* info */
	char *fn; /* name */
	FILE *fo; /* object */

	setvbuf(stdout, (char *)buf, _IOFBF, (sizeof buf)/(sizeof *buf));
	if(argc < 2){
		argv0 = argc > 0
			? argv[0]
			: program_name;
		argv -= argv[0] == NULL;
		goto simple;
	}

	while((c = getopt(argc, argv, "hu")) != -1)
		switch(c){
			case 'u':
				setvbuf(stdout, NULL, _IONBF, 0);
				continue;
			default:
				fprintf(stderr, "Usage: %s (-h) (file...)\n",
					argv[0]);
				return EX_USAGE;
		}

	argv0 = argv[0];
	argv += optind;

	while(*argv != NULL){
		if(argv[0][0] == '-' && argv[0][1] == '\0') /* "-" */
simple:			fo = stdin;
		else{
			fn = argv[0];
			if(stat(fn, &fi) == -1){
				fprintf(stderr, "%s: %s: %s\n", argv0, fn,
					strerror(errno));
				switch(errno){
				case EFAULT: case ENOENT: case ENOTDIR:
					return EX_NOINPUT;
				case EBADF: case EINVAL: case ENOMEM:
				case EOVERFLOW:
					return EX_OSERR;
				case ELOOP: case ENAMETOOLONG:
					return EX_DATAERR;
				}
			}
			if(S_ISDIR(fi.st_mode)){
				fprintf(stderr, "%s: %s: Is a directory\n",
					argv[0], fn);
				return EX_DATAERR;
			}
			if((fo = fopen(fn, "r")) == NULL){
				fprintf(stderr,
					"%s: %s: %s\n",
					argv0, fn, strerror(errno));
				return EX_OSERR;
			}
		}

		while((c = getc(fo)) != EOF)
			if(putc(c, stdout) == EOF){
				fprintf(stderr,
					"%s: Exiting due to error writing to"
					" output...\n",
					argv0);
				fclose(fo);
				return EX_UNAVAILABLE;
			}

		if(fo != stdin)
			fclose(fo);

		++argv;
	}

	return EX_OK;
}