/* -------------------------------------------------------------------- */
/* gs_character.c							*/
/*									*/
/*  Copyright (C) 1997,1998,1999,2000 Angelo Masci			*/
/*									*/
/*  This library is free software; you can redistribute it and/or	*/
/*  modify it under the terms of the GNU Library General Public		*/
/*  License as published by the Free Software Foundation; either	*/
/*  version 2 of the License, or (at your option) any later version.	*/
/*									*/
/*  This library is distributed in the hope that it will be useful,	*/
/*  but WITHOUT ANY WARRANTY; without even the implied warranty of	*/
/*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU	*/
/*  Library General Public License for more details.			*/
/*									*/
/*  You should have received a copy of the GNU Library General Public	*/
/*  License along with this library; if not, write to the Free		*/
/*  Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.	*/
/*									*/
/*  You can contact the author at this e-mail address:			*/
/*									*/
/*  angelo@styx.demon.co.uk						*/
/*									*/
/* -------------------------------------------------------------------- */
/* $Id$
   -------------------------------------------------------------------- */

#include <stdio.h>
#include <ctype.h>
#include <unistd.h>
#include <errno.h>

#include "gs_private.h"

/* -------------------------------------------------------------------- */

#define MAX_CHARACTER_STACK 32

static char character_stack[MAX_CHARACTER_STACK];
static int  character_stack_top = 0;

/* -------------------------------------------------------------------- */

static int readchar(int fd, unsigned char *c);

/* -------------------------------------------------------------------- */
/* -------------------------------------------------------------------- */
static int readchar(int fd, unsigned char *c)
{
	int res;

	do 
	{	res = read(fd, c, 1);

	} while ((res == -1) && (errno == EINTR));

	if (res == 0)
	{	*c = (unsigned char)EOF;
	}
	
	return res;
}

/* -------------------------------------------------------------------- */
/* If we have pushed back a character then return it, else		*/
/* return the next character.						*/
/* -------------------------------------------------------------------- */
int gs_get_next_character(int fd, unsigned char *character)
{
	int 	res;


	if (gs_pop_character(character) != -1)
	{	return 0;
	}

	res = readchar(fd, character);
	if (res == -1)
	{	return -1;
	}

	if (*character == '#')
	{
		do
		{	res = readchar(fd, character);
			if (res == -1)
			{	return -1;
			}

		} while ((*character != '\n') && (*character != (unsigned char)EOF));
	}

	if (*character == '\n')
	{	gs_increment_linenumber();
	}

	return 0;
}

/* -------------------------------------------------------------------- */
/* -------------------------------------------------------------------- */
int gs_push_character(unsigned char character)
{
	if (character_stack_top == MAX_CHARACTER_STACK)
	{	return -1;
	}

	character_stack[character_stack_top] = character;
	character_stack_top++;

	if (character == '\n')
	{	gs_decrement_linenumber();
	}

	return 0;
}


/* -------------------------------------------------------------------- */
/* -------------------------------------------------------------------- */
int gs_pop_character(unsigned char *character)
{
	if (character_stack_top == 0)
	{	return -1;
	}

	character_stack_top--;
	*character = character_stack[character_stack_top];

	if (*character == '\n')
	{	gs_increment_linenumber();
	}

	return 0;
}


/* -------------------------------------------------------------------- */
/* -------------------------------------------------------------------- */
int gs_escape_character(int fd, unsigned char *escaped_character)
{
	unsigned
	char 	character;

	if (gs_get_next_character(fd, &character) == -1)
	{	return -1;
	}

	if (character == 'a')
	{	*escaped_character = '\f';
	}
	else
	if (character == 'b')
	{	*escaped_character = '\b';
	}
	else
	if (character == 'f')
	{	*escaped_character = '\f';
	}
	else
	if (character == 'n')
	{	*escaped_character = '\n';
	}
	else
	if (character == 'r')
	{	*escaped_character = '\r';
	}
	else
	if (character == 't')
	{	*escaped_character = '\t';
	}
	else
	if (character == 'v')
	{	*escaped_character = '\v';
	}
	else
	if (character == 'x')
	{
		int	low_nibble,
			high_nibble,
			high_character,
			low_character;

		if (gs_get_next_character(fd, &character) == -1)
		{	return -1;
		}

		high_character = character;

		if (isxdigit(character))
		{
			if ((character >= '0') && (character <= '9'))
			{
				high_nibble = (character - '0') << 4;
			}
			else
			if ((character >= 'a') && (character <= 'f'))
			{	
				high_nibble = (10 + (character - 'a')) << 4;
			}
			else
			{	high_nibble = (10 + (character - 'A')) << 4;
			}

			if (gs_get_next_character(fd, &character) == -1)
			{	return -1;
			}

			low_character = character;


			if (isxdigit(character))
			{
				if ((character >= '0') && (character <= '9'))
				{
					low_nibble = (character - '0');
				}
				else
				if ((character >= 'a') && (character <= 'f'))
				{	
					low_nibble = (10 + (character - 'a'));
				}
				else
				{	low_nibble = (10 + (character - 'A'));
				}

				*escaped_character = high_nibble + low_nibble;
			}		
			else
			{
				/* Error */

				gs_push_character('x');
				gs_push_character(high_character);
				gs_push_character(low_character);

				*escaped_character = '\\';
			}
		}
		else
		{	
			/* Error */

			gs_push_character('x');
			gs_push_character(high_character);

			*escaped_character = '\\';
		}
	}
	else
	if (character == '\\')
	{	*escaped_character = '\\';
	}
	else
	if (character == '\"')
	{	*escaped_character = '\"';
	}
	else
	if (character == '\'')
	{	*escaped_character = '\'';
	}
	else
	{
		/* Error */

		gs_push_character(character);
		*escaped_character = '\\';
	}

	return 0;
}