/*
 * fopen
 * This function is quite different from the function of the same
 * name in the BDS C Standard Library. It is also different from
 * the function used in almost every implementation of the U**X
 * Standard C Library (they vary wildly in what `mode' means).
 * This version of fopen accepts 4 types of modes as follows:
 * "r", read mode, opens an existing file for read only. "w", write
 * mode, opens a new file for writing clobbering any existing files
 * of the same name. If the file is read only it returns NULL. "u",
 * update mode, opens an existing file for read/write faccess. If
 * the file is read only, it returns NULL. "a", append mode opens
 * an existing file for read/write with the file pointer at the
 * end of the file. It also returns NULL if the file is read only.
 * Edit of 7/8/83
 */

FILE *
fopen(filename,mode)
char *filename, *mode;
{
	FILE *stream;
	int i, omode;

	if (filename == NULL || mode == NULL)
		return NULL;
	for (i = 0; i < _NFILE; i++) {	/* look for a buffer	*/
		if (filebuf[i]._base == NULL)
			break;		/* got an io buffer	*/
		if (i == (_NFILE - 1))	/* no buffers available	*/
			return NULL;
	}
	stream = (&filebuf[i]);		/* assign the io buffer	*/
	if ((stream -> _base = malloc(BUFSIZ)) == NULL)
		return NULL;
	if (mode[0] == 'r')
		omode = 0;
	if (mode[0] == 'w') {
		if (faccess(filename,2)<0)
			if (faccess(filename,0) == 0) {
				free(stream -> _base);
				stream -> _base = NULL;
				return NULL;
			}
		if ((stream->_fd=creat(filename))<0) {
			free(stream -> _base);
			stream -> _base = NULL;
			return NULL;
		}
		stream -> _nextp = stream -> _base;
		stream -> _nleft = BUFSIZ;
		stream -> _flag = _IOWRT;
		return stream;
	}
	if (mode[0] == 'u' || mode[0] == 'a') {
		omode = 2;
		if (faccess(filename,2)<0)
			if (faccess(filename,0) == 0) {
				free(stream -> _base);
				stream -> _base = NULL;
				return NULL;
			}
	}
	if ((stream -> _fd = open(filename,omode))<0) {
		free(stream -> _base);
		stream -> _base = NULL;
		return NULL;
	}
	if (mode[0] == 'a')
		seek(stream->_fd,0,2);
	stream -> _nleft = 0;
	stream -> _flag = 0;
	if (omode = 0)
		stream -> _flag |= _IOREAD;
	stream -> _flag |= _IOWRT;
	return stream;
}

/*
 * fclose
 * Conforms very closely to the function in the Version 7 U**X
 * Standard C Library. It closes the specified stream, flushes
 * the i/o buffer and frees the i/o buffer used bye the stream.
 * Last Edit 7/1/83
 */

int
fclose(stream)
FILE *stream;
{
	int i;
	if (isatty(stream))		/* can't close a tty	*/
		return ERROR;
	fflush(stream);			/* flush the io buffer	*/
	i = close(stream -> _fd);	/* close the file	*/
	free(stream -> _base);		/* free the io buffer	*/
	return 0;
}

/*
 * fflush
 * This performs essentially the same task as the function
 * of the same name in the BDS C 1.5 Standard library. It
 * need not be invoked before calls to fclose to assure
 * that the i/o buffer is flushed.
 * Last Edit 7/1/83
 */

int
fflush(stream)
FILE *stream;
{
	int i;
	if (isatty(stream))
		return 0;
	if (stream -> _nleft == BUFSIZ)
		return 0;
	i = NSECTS - stream -> _nleft / SECSIZ;
	if (write(stream -> _fd, stream -> _base, i) != i)
			return ERROR;
	i = (i-1) * SECSIZ;
	if (stream -> _nleft) {
		movmem(stream -> _base + i, stream -> _base, SECSIZ);
		stream -> _nleft += i;
		stream -> _nextp -= i;
		return seek(stream->_fd, -1, 1);
	}
	stream -> _nleft = BUFSIZ;
	stream -> _nextp = stream -> _base;
	return 0;
}