/* *****************************************************************************
 * decode/std/picture.c -- decode a picture 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>
#include <zlib.h>

/* ************************************************************************** */
/*  Obfuscation-related functions                                             */
/* ************************************************************************** */
/**
 *	g3p_deobfuscate:
 *	De-obfuscate the image data.
 *
 *	@arg	buf			the buffer.
 *	@arg	n			the buffer size.
 */

static void g3p_deobfuscate(uint8_t *buf, size_t n)
{
	while (n--) {
		int byte = *buf;
		*buf++ = ~((byte << 5) | (byte >> 3)) & 0xFF;
	}
}

/* ************************************************************************** */
/*  Prizm Picture decoding function                                           */
/* ************************************************************************** */
/**
 *	g1m_decode_std_g3p:
 *	Decode a G3P file.
 *
 *	@arg	handle		the handle.
 *	@arg	buffer		the buffer to read from.
 *	@arg	std			the standard header.
 *	@arg	pic			the standard picture header.
 *	@return				the error code (0 if ok).
 */

int g1m_decode_std_g3p(g1m_t **h, g1m_buffer_t *buffer,
	struct standard_header *std, struct standard_picheader *pic)
{
	int err; *h = NULL;
	uint8_t *defbuf = NULL, *infbuf = NULL;

	/* start a checksum */
	uint32_t check = g1m_checksum32((void*)std,
		sizeof(struct standard_header), 0);
	check = g1m_checksum32((void*)pic,
		sizeof(struct standard_picheader), check);

	/* read the image header */
	DREAD(ihd, g3p_subheader)
	check = g1m_checksum32(&ihd, sizeof(struct g3p_subheader), check);
	unsigned int width = be16toh(ihd.width), height = be16toh(ihd.height);
	int color_depth = be16toh(ihd.color_depth);

	/* log info */
	log_info("Width: %upx, height: %upx", width, height);
	log_info("Pixel depth: %s",
		(color_depth == g3p_color_4bit) ? "4-bit" : "16-bit");
	log_info("Generator ID: 0x%04X", be16toh(ihd.generator_id));
	log_info("-");

	/* read deflated image */
	size_t deflated_image_size = be32toh(ihd.data_size) - 6;
	log_info("Reading %" PRIuSIZE "B of deflated data", deflated_image_size);
	err = g1m_error_alloc;
	defbuf = malloc(deflated_image_size);
	if (!defbuf) goto fail;
	READ(defbuf, deflated_image_size)

	/* unobfuscate if required */
	int is_obfuscated =
		((std->obfuscated + 8) & 0xff) != ((std->filesize & 0xff00) >> 8);
	if (is_obfuscated) {
		log_info("Is obfuscated, let's deobfuscate!");
		g3p_deobfuscate(defbuf, deflated_image_size);
	}

	/* make the destination buffer */
	size_t rawsize = color_depth == g3p_color_4bit
		? g1m_picturesize_4bit_code(width, height)
		: g1m_picturesize_16bit(width, height);
	err = g1m_error_alloc;
	infbuf = malloc(rawsize);
	if (!infbuf) goto fail;

	/* uncompress */
	uLongf inflated_size = 0L; // rawsize?
	int z_err = uncompress(infbuf, &inflated_size, defbuf, deflated_image_size);
	if (z_err) {
		log_fatal("Zlib error: error #%d", z_err);
		err = g1m_error_magic;
		goto fail;
	}
	free(defbuf); defbuf = NULL;

	/* check the checksum */
	uint32_t checksum; READ(&checksum, sizeof(uint32_t))
	uLong adl = adler32(0, defbuf, deflated_image_size);
	if (adl != (uLong)checksum) {
		log_fatal("Incorrect Adler32 checksum!");
		log_fatal("Expected 0x%08" PRIX32 ", got 0x%08lX",
			checksum, adl);
		err = g1m_error_checksum;
		goto fail;
	}

	/* make the handle */
	err = g1m_make_picture(h, ihd.width, ihd.height);
	if (err) goto fail;
	g1m_t *handle = *h;

	/* then store it */
	g1m_decode_picture(handle->pixels, ihd.color_depth == g3p_color_4bit
		? g1m_pictureformat_4bit_code : g1m_pictureformat_16bit,
		infbuf, handle->width, handle->height);
	free(infbuf); infbuf = NULL;

	/* TODO: footers? */

	/* no error */
	return (0);
fail:
	g1m_free(*h); *h = NULL;
	free(infbuf); free(defbuf);
	return (err);
}

/* ************************************************************************** */
/*  Classpad Picture decoding function                                        */
/* ************************************************************************** */
/**
 *	g1m_decode_std_c2p:
 *	Decode Classpad images.
 *
 *	@arg	handle		the handle.
 *	@arg	buffer		the buffer to read from.
 *	@arg	std			the standard header.
 *	@arg	pic			the standard picture header.
 *	@return				the error code (0 if ok).
 */

int g1m_decode_std_c2p(g1m_t **h, g1m_buffer_t *buffer,
	struct standard_header *std, struct standard_picheader *pic)
{
	(void)h; (void)buffer;
	(void)std; (void)pic;
	/* TODO */
	log_info("C2P files are not managed yet.");

	/* no error */
	return (g1m_error_magic);
}