/*	INPUT AND BUFFER HANDLING MODULE	*/

/*
	[input.X inp_pkg.spec input.h]
	Input buffering module: this module contains the routines that
	offers an input buffering mechanism to the user.

	This module exports the following objects:
	input.h :	an include-file, which must be included when using
			this module
	InsertFile() :	suspend input from current buffer and obtain the
			next input characters from the specified file
	InsertText() :	suspend input from current buffer and take the
			specified text as stream of input characters
	LoadChar() :	(defined in input.h) read next character from
			the input ; LoadChar() invokes loadbuf() on
			encounting a ASCII NUL character
	PushBack() :	(defined in input.h) push last character back onto
			the input stream; NPUSHBACK characters of pushback
			are guaranteed, provided that they have all been read
			from the current input stream
	AtEoIT() :	this routine is called at the end of an inserted text.
			A default one is provided, which does nothing.
	AtEoIF() :	this routine is called at the end of an inserted file.
			A default one is provided, which does nothing.
	
	Imported objects are:
	INP_NPUSHBACK, INP_READ_IN_ONE, INP_TYPE, INP_VAR,
	routines from the "alloc" package, routines from the "storage"
	package, and routines from the "system" package.

	INP_READ_IN_ONE defined: every input file is read into memory completely
		and made an input buffer. Only use it if the size of a file
		fits always fits in an integer and you have lots of memory.
	INP_READ_IN_ONE not defined: the input from files is buffered in
		a fixed length input buffer
	INP_NPUSHBACK: the number of characters pushback
*/

#include <alloc.h>
#include <system.h>

#ifndef INP_NPUSHBACK
#define INP_NPUSHBACK 1
#endif

#if INP_NPUSHBACK < 1
#define INP_NPUSHBACK 1
#endif

#ifndef INP_BUFSIZE
#define INP_BUFSIZE BUFSIZ
#endif

#if INP_NPUSHBACK > INP_BUFSIZE/2
Now this is really ridiculous! You deserve what you get!!
#endif

#ifdef INP_TYPE
extern INP_TYPE INP_VAR;
#endif INP_TYPE

#ifdef DEBUG
#define PRIVATE
#else
#define PRIVATE static
#endif

struct buffer_header	{
	struct buffer_header *next;
	int bh_size;	/* = strlen (text), should be unsigned	*/
	char *bh_text;	/* pointer to buffer containing text	*/
	char *bh_ipp;	/* current read pointer (= stacked ipp)	*/
#ifdef INP_TYPE
	INP_TYPE bh_i;	/* user defined */
#endif INP_TYPE
	File *bh_fd;	/* A file descriptor in case of a file */
	char bh_eofreturned;	/* set if we returned eof for this buffer */
};

#ifndef INP_READ_IN_ONE
struct i_buf {
	struct i_buf *next;
	char ib_text[INP_BUFSIZE+INP_NPUSHBACK];
};

# endif not INP_READ_IN_ONE

char *_ipp;
PRIVATE struct buffer_header *head;

#ifdef INP_READ_IN_ONE
/*	readfile() creates a buffer in which the text of the file
	is situated.  A pointer to the start of this text is
	returned.  *size is initialized with the buffer length.
*/

PRIVATE int
readfile(fd, fn, size, pbuf)
	register File *fd;
	char *fn;		/* file name */
	register long *size;
	extern long sys_filesize();
	char **pbuf;		/* output parameter */
{
	int rsize;

	if (
	     (*size = sys_filesize(fn)) < 0
	   ||
	     ((unsigned) (*size + 1) != (*size + 1))
	   ||
	     !(*pbuf = malloc((unsigned) (*size + 1)))) {
		sys_close(fd);
		return 0;
	}
	if (
	     !sys_read(fd, *pbuf, (int) *size, &rsize)
	   ||
	     *size != rsize
	   )  {
		sys_close(fd);
		free(*pbuf);
		return 0;
	}
	sys_close(fd);
	(*pbuf)[*size] = '\0';	/* invoke loadbuf() at end */
	return 1;
}
#endif INP_READ_IN_ONE

#ifndef INP_READ_IN_ONE
/*	Input buffer supplying routines: pushbuf()
*/

PRIVATE struct i_buf *i_ptr;

PRIVATE char *
pushbuf()
{
	register struct i_buf *ib = 
		(struct i_buf *) malloc(sizeof(struct i_buf));

	if (!ib) return 0;
	ib->next = i_ptr;
	i_ptr = ib;

	/*	Don't give him all of it, we need some to implement a good
	   	PushBack
	*/
	return &(ib->ib_text[INP_NPUSHBACK-1]);
}
#endif not INP_READ_IN_ONE

/*	Input buffer administration: push_bh() and pop_bh()
*/
PRIVATE struct buffer_header *
push_bh()
{
	register struct buffer_header *bh;

	if (bh = head) {
		bh->bh_ipp = _ipp;
#ifdef INP_TYPE
		bh->bh_i = INP_VAR;
#endif INP_TYPE
	}
	if (!(bh = (struct buffer_header *)malloc(sizeof(struct buffer_header)))) return 0;
	bh->next = head;
	bh->bh_eofreturned = 0;
	head = bh;
	return bh;
}

/*	pop_bh() uncovers the previous inputbuffer on the stack
	of headers.  0 is returned if there are no more
	inputbuffers on the stack, 1 is returned in the other case.
*/
PRIVATE int
pop_bh()
{
	register struct buffer_header *bh = head;

	if (bh->bh_fd) {	/* unstack a file */
#ifndef INP_READ_IN_ONE
		struct i_buf *ib;

		ib = i_ptr->next;
		free((char *) i_ptr);
		i_ptr = ib;
#else INP_READ_IN_ONE
		free(bh->bh_text);
#endif INP_READ_IN_ONE
	}

	bh = bh->next;
	free((char *) head);
	head = bh;

	if (!bh)	{	/* no more entries */
		head = (struct buffer_header *) 0;
		return 0;
	}

	_ipp = bh->bh_ipp;	/* restore previous input pointer */
#ifdef INP_TYPE
	INP_VAR = bh->bh_i;
#endif INP_TYPE

	return 1;
}

#ifndef INP_READ_IN_ONE
/*	low level I/O routine : read one block from current input
	stream : readblock
*/

PRIVATE int
readblock(fd, buf, n)
	File *fd;
	char buf[];
	int *n;
{

	if (!sys_read(fd, buf, INP_BUFSIZE, n)) {
		return 0;
	}
	buf[*n] = '\0';
	return 1;
}
#endif not INP_READ_IN_ONE

/*	Miscellaneous routines :
	mk_filename()
*/

/*	mk_filename() concatenates a dir and filename.
*/
PRIVATE int
mk_filename(dir, file, newname)
	register char *dir, *file;
	char **newname;
{

	register char *dst;

	dst = malloc((unsigned) (strlen(dir) + strlen(file) + 2));
	if (!dst) return 0;
	*newname = dst;
	while (*dst++ = *dir++);
	*--dst = '/';
	while (*++dst = *file++);
	return 1;
}

/*	Interface routines : InsertFile, InsertText, and loadbuf
*/

int
InsertFile(filnam, table, result)
	char *filnam;
	char *table[];
	char **result;
{
	char *newfn = 0;

#ifdef INP_READ_IN_ONE
	char *text;
	long size;
#endif INP_READ_IN_ONE
	File *fd = 0;

	if (!filnam) fd = STDIN;
	else {
		if (table == 0 || filnam[0] == '/') {
				/* don't look in the table! */
			if (!sys_open(filnam, OP_READ, &fd)) return 0;
		}
		else {
			while (*table) {	
				/* look in the directory table */
				if (!mk_filename(*table++, filnam, &newfn)) {
					return 0;
				}
				if (sys_open(newfn, OP_READ, &fd)) {
					/* free filnam ??? NO we don't know 
					   where it comes from!
					*/
					filnam = newfn;
					break;
				}
				free(newfn);
				newfn = 0;
			}
		}
	}

	if (fd) {
		struct buffer_header *push_bh();
		register struct buffer_header *bh = push_bh();

		if (!bh) {
			if (fd != STDIN) sys_close(fd);
			return 0;
		}
#ifdef INP_READ_IN_ONE
		if (fd == STDIN) return 0;	/* illegal */
		if (!readfile(fd, filnam, &size, &text)) {
			sys_close(fd);
			return 0;
		}
		bh->bh_size = size;
		_ipp = bh->bh_text = text;
#else not INP_READ_IN_ONE
		if (
		     !(_ipp = bh->bh_text = pushbuf())
		   ||
		     !readblock(fd,_ipp,&(bh->bh_size))) {
			if (fd != STDIN) sys_close(fd);
			return 0;
		}
#endif INP_READ_IN_ONE
		bh->bh_fd = fd;	/* this is a file */
		*result = filnam;
		return 1;
	}
	return 0;
}

int
InsertText(text, length)
	char *text;
{
	struct buffer_header *push_bh();
	register struct buffer_header *bh = push_bh();

	if (!bh) return 0;
	bh->bh_size = (long) length;
	_ipp = bh->bh_text = text;
	bh->bh_fd = 0;	/* No file! */
	return 1;
}

/*	loadbuf() is called if LoadChar meets a '\0' character
	which may be the end-of-buffer mark of the current input
	buffer.  The '\0' could be genuine although not likely.
	Note: this routine is exported due to its occurence in the definition
	of LoadChar [input.h], that is defined as a macro.
*/
int
loadbuf()
{
	register struct buffer_header *bh = head;
	static char buf[INP_NPUSHBACK + 1];
	int FromFile;

	if (!bh) {		/* stack exhausted, EOF on sourcefile */
		return EOI;
	}

	if (_ipp < &(bh->bh_text[bh->bh_size])) {
				/* a genuine '\0' character has been seen */
		return '\0';
	}

	FromFile = (bh->bh_fd != 0);

#ifndef INP_READ_IN_ONE
	if (FromFile) {
#if INP_PUSHBACK > 1
		register char *so = &(bh->bh_text[bh->bh_size]);
		register char *de = bh->bh_text;
		register int i = INP_NPUSHBACK - 1;

		while (i-- > 0) {
				/* make sure PushBack will work */
			*--de = *--so;
		}
#endif
		if (
		     readblock(bh->bh_fd, bh->bh_text, &(bh->bh_size)) 
		   &&
		     bh->bh_size > 0
		   ) {
			_ipp = bh->bh_text;
			return *_ipp++;
		}
	}

#endif not INP_READ_IN_ONE

	if (!bh->bh_eofreturned) {
		bh->bh_eofreturned = 1;
		_ipp--;
		if (FromFile) {
			if (AtEoIF()) return EOI;
		}
		else {
			if (AtEoIT()) return EOI;
		}
	}

#ifndef INP_READ_IN_ONE
	if (FromFile && bh->bh_fd != STDIN) sys_close(bh->bh_fd);
#endif not INP_READ_IN_ONE

	if (pop_bh()) {
		if (*_ipp) return *_ipp++;
		return loadbuf();
	}
	_ipp = &buf[INP_NPUSHBACK];
	return EOI;
}