/* *****************************************************************************
 * decode/main.c -- decode a 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/>.
 * ************************************************************************** */
#include <libg1m/internals.h>

/* ************************************************************************** */
/*  Check using extensions                                                    */
/* ************************************************************************** */
/* Decode function */
typedef int (*decode_func)(g1m_handle_t**, g1m_buffer_t*);

/* Correspondance type */
struct corresp {
	/* extension */
	const char *ext;

	/* expected types */
	g1m_type_t type;

	/* function */
	decode_func decode;
};

/* Correspondances */
static struct corresp correspondances[] = {
//	{"g1s", g1m_type_storage, g1m_decode_storage},

	/* terminating entry */
	{NULL,  0,                NULL}
};

/**
 *	lookup_extension:
 *	Get the function using the type.
 *
 *	@arg	path	the path.
 *	@arg	types	the expected types.
 *	@arg	decode	the decode function to set.
 *	@return			the error code (0 if ok).
 */

static int lookup_extension(const char *path, g1m_type_t types,
	decode_func *func)
{
	/* match the extension */
	char ext[5];
	if (!g1m_getext(path, ext, 5)) return (g1m_error_magic);
	struct corresp *c = correspondances - 1;
	while ((++c)->ext) if (!strcmp(c->ext, ext)) break;

	/* check if correspondance is valid and expected */
	if (!c->ext) return (g1m_error_magic);
	if (types && !(types & c->type)) return (g1m_error_wrong_type);

	/* return the decode function */
	*func = c->decode;
	return (0);
}

/* ************************************************************************** */
/*  Main decoding function                                                    */
/* ************************************************************************** */
/**
 *	g1m_decode:
 *	Decode a file.
 *
 *	Read the standard header, correct endianness, check magic numbers,
 *	then read subparts according to the G1M type.
 *
 *	@arg	handle			the handle.
 *	@arg	path			the file path.
 *	@arg	buffer			the buffer to read from.
 *	@arg	expected_types	the expected types.
 *	@return					the error code (0 if ok).
 */

int g1m_decode(g1m_handle_t **handle, const char *path, g1m_buffer_t *buffer,
	g1m_type_t expected_types)
{
	/* match using extension */
	decode_func decode;
	int err = lookup_extension(path, expected_types, &decode);
	if (err == g1m_error_wrong_type) return (err);
	else if (!err) return ((*decode)(handle, buffer));

	/* identify a CAS file */
	unsigned char buf[0x20]; READ(buf, 1)
	if (buf[0] == ':') {
		if (expected_types && !(expected_types & g1m_type_mcs))
			return (g1m_error_wrong_type);
		return (g1m_decode_cas(handle, buffer));
	}

	/* identify a GraphCard file */
	READ(&buf[1], 2)
	if (!buf[0] && buf[1] == 0x32 && buf[2] == ':') {
		if (expected_types && !(expected_types & g1m_type_mcs))
			return (g1m_error_wrong_type);
		return (g1m_decode_grc(handle, buffer));
	}

	/* identify a Casemul file */
	READ(&buf[3], 9)
	int casemul_be = !memcmp(buf, "CAFS", 4);
	if (casemul_be || !memcmp(buf, "ACFS", 4)) {
		g1m_casemul_intheader_t *ch = (void*)buf;
		uint32_t ver = casemul_be ? be32toh(ch->g1m_casemul_intheader_version)
			: le32toh(ch->g1m_casemul_intheader_version);
		uint32_t siz = casemul_be ? le32toh(ch->g1m_casemul_intheader_size)
			: le32toh(ch->g1m_casemul_intheader_size);
		if (ver != 0x100 || siz != sizeof(g1m_casemul_header_t))
			return (g1m_error_magic);
		if (expected_types && !(expected_types & g1m_type_mcs))
			return (g1m_error_wrong_type);
		return (g1m_decode_casemul(handle, buffer, casemul_be));
	}

	/* identify a standard header (send a _copy_) */
	READ(&buf[12], 0x14)
	uint8_t altbuf[0x20]; memcpy(altbuf, buf, 0x20);
	return (g1m_decode_std(handle, path, buffer,
		(g1m_standard_header_t*)altbuf, expected_types));
}