/* *****************************************************************************
 * libg1m/format.h -- the G1M format description.
 * 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/>.
 * ************************************************************************** */
#ifndef LIBG1M_FORMAT_H
# define LIBG1M_FORMAT_H
# include <stdint.h>
# pragma pack(1)

/*	Welcome on this new episode of Monster Circus! Today we'll present to you
 *	something that you might not be able to forget: the G1M format.
 *
 *	This format is used by CASIO with its calculator for storing things
 *	like add-ins (compiled programs), MCS (main memory saves), and others.
 *	In fact, there is no name for the general format, only names for the
 *	"subformats" based on this one.
 *
 *	It all starts with a header, called Standard Header by Simon Lothar.
 *	This Standard Header contains the total filesize, the G1M type (add-in,
 *	MCS, e-acts), some data that will be useful for the MCS type, and some
 *	magic and control bytes.
 *
 *	For some reason, this StandardHeader is INVERTED on every file it's on,
 *	you will have to apply a NOT operation on its bytes for it to make sense.
 *
 *	Keep in mind that, everywhere in the header, multi-bytes integers
 *	are BIG ENDIAN.
 *
 *	The LSB is the Least Significant Byte: once adapted to the host endianness,
 *	it can simply be obtained by bitwise-AND-ing with 0xff. */

struct standard_header {
	/* the file identifier */
	uint8_t main_id[8];

	/* our subtype! */
	uint8_t subtype[6];

	/* first control byte: filesize LSB + 0x41 */
	uint8_t control;

	/* said to be 0x01, but doesn't need to */
	uint8_t align_one;

	/* total filesize */
	uint32_t filesize;

	/* second control byte: filesize LSB + 0xb8 */
	uint8_t control2;

	/* alignment */
	uint8_t align[8];

	/* is obfuscated - useful for G3P */
	uint8_t obfuscated;

	/* number of objects contained (useful for MCS filetype) */
	uint16_t number;
};

/*	At the beginning, we thought "USBPower" was some magic sequence we would
 *	systematically find in the "main_id" field. But counter examples came:
 *	the G3L, whose main ID was "Ly755   ", and the C2P.
 *
 *	We also thought the subtype was only one-byte long, but the C2P came along
 *	with its "c2p\0\0\0" subtype.
 *
 *	All main ID/types correspondances are in the `src/utils/type.c` file.
 *	From a user program, you can use the functions
 *	in `include/libg1m/formatutils.h`. */

# pragma pack()

/*	After the Standard Header is read and the type is read, we have parts,
 *	each with their own subheaders and their own subtilities.
 *
 *	Where do you want to start? Pick your poison. */

# include <libg1m/format/addin.h>
# include <libg1m/format/eact.h>
# include <libg1m/format/mcs.h>
# include <libg1m/format/storage.h>
# include <libg1m/format/picture.h>
# include <libg1m/format/lang.h>
# include <libg1m/format/fkey.h>
#endif /* LIBG1M_FORMAT_H */