#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include "stdio.h"

#define PERMS	0666

FILE _iob[OPN_MAX] = {
	{0, (char *) NULL, (char *) NULL, {1, 0, 0, 1, 0, 0}, 0},
	{0, (char *) NULL, (char *) NULL, {0, 1, 0, 1, 0, 0}, 1},
	{0, (char *) NULL, (char *) NULL, {0, 1, 1, 0, 0, 0}, 2},
};

FILE *fopen(char *name, char *mode)
{
	int fd;
	FILE *fp;

	if (*mode != 'r' && *mode != 'w' && *mode != 'a')
		return NULL;

	for (fp = _iob; fp < _iob + OPN_MAX; ++fp)
		if (fp->flag.is_read == 0 && fp->flag.is_write == 0)
			break;
	if (fp == _iob + OPN_MAX)
		return NULL;

	if (*mode == 'w') {
		fd = creat(name, PERMS);
	} else if (*mode == 'a') {
		if ((fd = open(name, O_WRONLY)) == -1)
			fd = creat(name, PERMS);
		lseek(fd, 0L, 2);
	} else {
		fd = open(name, O_RDONLY);
	}

	if (fd == -1)
		return NULL;

	fp->fd = fd;
	fp->cnt = 0;
	fp->base = NULL;
	fp->flag.is_unbuf = 0;
	fp->flag.is_buf = 1;
	fp->flag.is_eof = 0;
	fp->flag.is_err = 0;
	if (*mode == 'r') {
		fp->flag.is_read = 1;
		fp->flag.is_write = 0;
	} else {
		fp->flag.is_write = 1;
		fp->flag.is_read = 0;
	}

	return fp;
}

int _fillbuf(FILE *fp)
{
	int bufsize;

	if (fp->flag.is_read == 0 ||
	    fp->flag.is_err  == 1 ||
	    fp->flag.is_eof  == 1)
		return EOF;

	bufsize = (fp->flag.is_unbuf == 1) ? 1 : BUFSIZ;
	if (fp->base == NULL)
		if ((fp->base = (char *) malloc(bufsize)) == NULL)
			return EOF;
	fp->ptr = fp->base;
	
	fp->cnt = read(fp->fd, fp->base, bufsize);
	if (--fp->cnt < 0) {
		if (fp->cnt == -1)
			fp->flag.is_eof = 1;
		else
			fp->flag.is_err = 1;
		fp->cnt = 0;
		return EOF;
	}

	return (unsigned char) *fp->ptr++;
}