/* *****************************************************************************
 * decode/cas/cell.c -- decode a CAS matrix/list/variable.
 * Copyright (C) 2017 Thomas "Cakeisalie5" Touhey <thomas@touhey.fr>
 *
 * This file is part of libg1m.
 * libg1m is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 3.0 of the License,
 * or (at your option) any later version.
 *
 * libg1m 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with libg1m; if not, see <http://www.gnu.org/licenses/>.
 * ************************************************************************** */
#include <libg1m/internals.h>

/* ************************************************************************** */
/*  Internal function                                                         */
/* ************************************************************************** */
/**
 *	decode_cell:
 *	Read a cell.
 *
 *	@arg	buffer		the buffer to read from.
 *	@arg	cell		the cell to fill.
 *	@arg	x			the abscissa of the cell.
 *	@arg	y			the ordinate of the cell.
 *	@return				the error code (0 if ok).
 */

static int decode_cell(g1m_buffer_t *buffer, g1m_mcscell_t *cell,
	unsigned int *x, unsigned int *y)
{
	uint8_t csum = 0;
	cell->g1m_mcscell_flags = g1m_mcscellflag_used;

	/* read position */
	uint16_t fx, fy;
	READ(&fx, sizeof(uint16_t)) *x = be16toh(fx) - 1;
	READ(&fy, sizeof(uint16_t)) *y = be16toh(fy) - 1;
	csum += g1m_checksum8(&fx, sizeof(uint16_t));
	csum += g1m_checksum8(&fy, sizeof(uint16_t));

	/* read the parts */
	DREAD(wkg, g1m_casbcd_s)
	csum += g1m_checksum8(&wkg, sizeof(g1m_casbcd_t));
	if (g1m_bcd_fromcas(&wkg, &cell->g1m_mcscell_real)) {
		READ(&wkg, sizeof(g1m_casbcd_t))
		csum += g1m_checksum8(&wkg, sizeof(g1m_casbcd_t));
		g1m_bcd_fromcas(&wkg, &cell->g1m_mcscell_imgn);
	}

	/* read and check the checksum */
	uint8_t checksum; READ(&checksum, sizeof(uint8_t))
	if (~csum + 1 != checksum)
		return (g1m_error_checksum);

	/* no prob'! */
	return (0);
}

/* ************************************************************************** */
/*  Cell-reading CAS part decoding functions                                  */
/* ************************************************************************** */
/**
 *	g1m_decode_caspart_matrix:
 *	Decode a CAS matrix part.
 *
 *	@arg	handle		the handle to contribute to.
 *	@arg	buffer		the buffer to read from.
 *	@return				the error code (0 if ok).
 */

int g1m_decode_caspart_matrix(g1m_mcsfile_t *handle, g1m_buffer_t *buffer)
{
	/* read the cell */
	g1m_mcscell_t cell; unsigned int y, x;
	int err = decode_cell(buffer, &cell, &x, &y);
	if (err) return (err);

	/* save the cell (FIXME: secure) */
	handle->g1m_mcsfile_cells[y][x] = cell;

	/* check if its the last cell */
	if (y == handle->g1m_mcsfile_head.g1m_mcshead_height - 1
	 && x == handle->g1m_mcsfile_head.g1m_mcshead_width - 1)
		handle->g1m_mcsfile_head.g1m_mcshead_flags &= ~g1m_mcsflag_unfinished;

	/* no error! */
	return (0);
}

/**
 *	g1m_decode_caspart_var:
 *	Decode a CAS variable part.
 *
 *	@arg	handle		the handle to contribute to.
 *	@arg	buffer		the buffer to read from.
 *	@return				the error code (0 if ok).
 */

int g1m_decode_caspart_var(g1m_mcsfile_t *handle, g1m_buffer_t *buffer)
{
	/* read and save the cell */
	unsigned int x, y;
	int err = decode_cell(buffer, &handle->g1m_mcsfile_var, &x, &y);
	if (err) return (err);
	if (x != 1 || y != 1) return (g1m_error_magic);

	/* no error! */
	handle->g1m_mcsfile_head.g1m_mcshead_flags &= ~g1m_mcsflag_unfinished;
	return (0);
}