/* *****************************************************************************
 * decode/fxi.c -- decode a fx-Interface file.
 * 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/>.
 *
 * FXI is the official fx-Interface format. It is an obfuscated, binary format.
 * It is partially described in the Casetta project documentation:
 * https://casetta.tuxfamily.org/formats/fxi
 * ************************************************************************** */
#include <libg1m/internals.h>
#define FREAD(TO, SZ) { \
	READ(TO, SZ) \
	deobf(TO, SZ); }
#define FDREAD(NAM, TYPE) { \
	DREAD(NAM, TYPE) \
	obf(&NAM, sizeof(struct TYPE)); }

/* ************************************************************************** */
/*  Obfuscation-related functions                                             */
/* ************************************************************************** */
/**
 *	obf:
 *	Obfuscate AND de-obfuscate a string.
 *
 *	The formula was found by Lephenixnoir, from Planète Casio, out of an array
 *	found by Alexis Soulard, from Casioland (with a 14-years time lapse, yay!).
 *
 *	The formula is an involution, which means the obfuscation and
 *	de-obfuscation is done using the same formula.
 *
 *	@arg	s	the string to deobfuscate.
 *	@arg	n	the string length.
 */

#define deobf(S, N) obf(S, N)
static void obf(unsigned char *s, size_t n)
{
	while (n--)
		*s++ ^= ~24;
}

/* ************************************************************************** */
/*  File header                                                               */
/* ************************************************************************** */
static unsigned char header =
	"\xD5\xD7\x1F" "f" "FX-INTERFACE - YELLOW COMPUTING" /* 35 */

	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" /* 20 */
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" "\x06"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" "\0\x07" /* entries total? */
	"\0\xFF\xFF" "\0\0\x0F\0"
	"CY" "CFXListItem"
	
	"NP\0\0"       "\x00" "\0\0\0" "\x00\0" "\x03\0"
	"\x15\x18" "\0\0\x00" "\0\x00" "\xA4\xA0"
	"\0\0\0\0\0\0\0\0" "\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"

	"\x01\x80\0\0" "\x01" "\0\0\0" "\x01\0" "\x03\0"
	"\x55\x1A" "\0\0\x04" "\0\x00" "\x5B\x80"
	"\0\0\0\0\0\0\0\0" "\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"

	"\x01\x80\0\0" "\x02" "\0\0\0" "\x02\0" "\x00\0"
	"\x08\x13" "\0\0\x22" "\0\x00" "\x83\x80"
	"\0\0\0\0\0\0\0\0" "\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"

	"\x01\x80\0\0" "\x03" "\0\0\0" "\x01\0" "\x03\0"
	"\x55\x1A" "\0\0\x20" "\0\x00" "\x1F\x81"
	"\0\0\0\0\0\0\0\0" "\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"

	"\x01\x80\0\0" "\x04" "\0\0\0" "\x02\0" "\x00\0"
	"\x08\x13" "\0\0\x21" "\0\x00" "\x83\x80"
	"\0\0\0\0\0\0\0\0" "\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"

	"\x01\x80\0\0" "\x05" "\0\0\0" "\x00\0" "\x02\0"
	"\x58\x10" "\0\0\x1E" "\0\x00" "\xCC\x80"
	"\0\0\0\0\0\0\0\0"  "\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"

	"\x01\x80\0\0" "\x06" "\0\0\0" "\x01\0" "\x00\0"
	"\x08\x11" "\0\0\x1E" "\0\x00" "\x83\x80"
	"\0\0\0\0\0\0\0\0"  "\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0" "\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"

	/* from here, it is a real file, SpeedSnk.fxi */

	"\x01" /* number of records? */ "\x00"

	"\x01\x80\0\0" "\x00" "\0\0\0" "\x02\0" "\x01\0"
	"\xBA\x1E" "\0\0\x22" "\0\x08" /* >program name size */
	"SpeedSnk" "\x83\x80" "\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
	"\0\0\0\0\0\0\0\0\0\0\0\0" "SpeedSnk"
	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"

	/* subheader? */
	"\0\0\0\0\0\0\0" "\0\1\0\1" "\0" "\xAF\x12"

	/* text file header */
	"TXT\0PG\0\0\x12\x81" "SpeedSnk"
	"\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"
	"NL" "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"

	/* ... program content */
	"\xFF" "\0\0\0\0\0\0"
;