/* This file is part of libmspack.
 * (C) 2003-2010 Stuart Caie.
 *
 * LZSS is a derivative of LZ77 and was created by James Storer and
 * Thomas Szymanski in 1982. Haruhiko Okumura wrote a very popular C
 * implementation.
 *
 * libmspack is free software; you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License (LGPL) version 2.1
 *
 * For further details, see the file COPYING.LIB distributed with libmspack
 */

#include "system-mspack.h"
#include "lzss.h"

#define ENSURE_BYTES do {				\
    if (i_ptr >= i_end) {				\
	read = system->read(input, &inbuf[0],		\
			    input_buffer_size);		\
        if (read <= 0) {				\
	    system->free(window);			\
	    return (read < 0) ? MSPACK_ERR_READ		\
		              : MSPACK_ERR_OK;		\
	}						\
        i_ptr = &inbuf[0]; i_end = &inbuf[read];	\
    }							\
} while (0)

#define WRITE_BYTE do {					\
    if (system->write(output, &window[pos], 1) != 1) {	\
	system->free(window);				\
	return MSPACK_ERR_WRITE;			\
    }							\
} while (0)

int lzss_decompress(struct mspack_system *system,
		    struct mspack_file *input,
		    struct mspack_file *output,
		    int input_buffer_size,
		    int mode)
{
    unsigned char *window, *inbuf, *i_ptr, *i_end;
    unsigned int pos, i, c, invert, mpos, len;
    int read;

    /* check parameters */
    if (!system || input_buffer_size < 1 || (mode != LZSS_MODE_EXPAND &&
        mode != LZSS_MODE_MSHELP && mode != LZSS_MODE_QBASIC))
    {
	return MSPACK_ERR_ARGS;
    }

    /* allocate memory */
    window = (unsigned char *) system->alloc(system, LZSS_WINDOW_SIZE + input_buffer_size);
    if (!window) return MSPACK_ERR_NOMEMORY;

    /* initialise decompression */
    inbuf = &window[LZSS_WINDOW_SIZE];
    memset(window, LZSS_WINDOW_FILL, (size_t) LZSS_WINDOW_SIZE);
    pos = LZSS_WINDOW_SIZE - ((mode == LZSS_MODE_QBASIC) ? 18 : 16);
    invert = (mode == LZSS_MODE_MSHELP) ? ~0 : 0;
    i_ptr = i_end = &inbuf[0];

    /* loop forever; exit condition is in ENSURE_BYTES macro */
    for (;;) {
	ENSURE_BYTES; c = *i_ptr++ ^ invert;
	for (i = 0x01; i & 0xFF; i <<= 1) {
	    if (c & i) {
		/* literal */
		ENSURE_BYTES; window[pos] = *i_ptr++;
		WRITE_BYTE;
		pos++; pos &= LZSS_WINDOW_SIZE - 1;
	    }
	    else {
		/* match */
		ENSURE_BYTES; mpos = *i_ptr++;
		ENSURE_BYTES; mpos |= (*i_ptr & 0xF0) << 4;
		len = (*i_ptr++ & 0x0F) + 3;
		while (len--) {
		    window[pos] = window[mpos];
		    WRITE_BYTE;
		    pos++;  pos  &= LZSS_WINDOW_SIZE - 1;
		    mpos++; mpos &= LZSS_WINDOW_SIZE - 1;
		}
	    }
	}
    }

    /* not reached */
    system->free(window);
    return MSPACK_ERR_OK;
}
