/* *****************************************************************************
 * decode/cas.c -- decode a CASIOLINK 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/>.
 *
 * Based on the Casetta project documentation:
 * https://casetta.tuxfamily.org/formats/cas
 * ************************************************************************** */
#include <libg1m/internals.h>
#define FUNC(NAME) g1m_decode_caspart_##NAME
#define HFUNC(NAME) g1m_decode_cashpart_##NAME

/* ************************************************************************** */
/*  Type correspondance list                                                  */
/* ************************************************************************** */
/* Part parsing function type */
typedef int (*cas_decode_function)(g1m_mcsfile_t*, g1m_buffer_t*);
typedef int (*cas_heads_decode_function)(g1m_mcshead_t *head,
	g1m_mcshead_t *heads, g1m_buffer_t *buffer);

/* Correspondance type */
struct cas_corresp {
	unsigned int type;
	cas_decode_function decode;
	cas_heads_decode_function hdecode;
};

/* All correspondances */
#define TTERM {0, NULL, NULL}
static struct cas_corresp cas_types[] = {
	{g1m_mcstype_var,     FUNC(var),     NULL},
	{g1m_mcstype_program, FUNC(program), NULL},
	{g1m_mcstype_matrix,  FUNC(matrix),  NULL},
	{g1m_mcstype_list,    FUNC(matrix),  NULL},
	{g1m_mcstype_capture, FUNC(capture), NULL},
	TTERM
};

/**
 *	lookup_cas_decode:
 *	Lookup for a parsing function for the CAS part.
 *
 *	@arg	type	the libg1m MCS file type.
 *	@return			the function (NULL if not found).
 */

static void *lookup_cas_decode(g1m_mcstype_t type, int heads)
{
	/* lookup for the type */
	struct cas_corresp *c = cas_types;
	while (c->decode) {
		if (type == c->type)
			break;
		c++;
	}

	/* return the function */
	return (heads ? (void*)c->hdecode : (void*)c->decode);
}

/* ************************************************************************** */
/*  Head decoding functions                                                   */
/* ************************************************************************** */
/**
 *	decode_cas50:
 *	Decode a CASIOLINK Protocol header.
 *
 *	@arg	head	the head to fill.
 *	@arg	buffer	the buffer to read from.
 *	@arg	csum	the current checksum.
 *	@return			if there was an error, or not.
 */

static int decode_cas50(g1m_mcshead_t *head, g1m_buffer_t *buffer, uint8_t csum)
{
	/* read the raw header */
	DREAD(hd, _cas50)
	log_info("Raw CAS50 (CASPRO) header content (app: '%.3s'):",
		head->g1m_mcshead_appname);
	logm_info(&hd, sizeof(struct _cas50));

	/* check the checksum */
	csum += g1m_checksum8(&hd, sizeof(struct _cas50) - 1);
	csum = ~csum + 1;
	if (csum != hd.checksum) {
		log_error("Checksum mismatch: expected 0x%02X, got 0x%02X",
			hd.checksum, csum);
		return (g1m_error_checksum);
	}

	/* copy the basic information */
	g1m_maketype_cas(head, (char*)hd.data);
	head->g1m_mcshead_size = be16toh(hd.height) - 2 /* checksum, colon */;
	char *end = memchr(hd.name, 0xFF, 8);
	size_t len = end ? (size_t)(end - (char*)hd.name) : 8;
	memcpy(head->g1m_mcshead_name, hd.name, len);
	head->g1m_mcshead_name[len] = 0;

	/* read specific data */
	switch (head->g1m_mcshead_type) {
	case g1m_mcstype_program:;
		/* copy password */
		head->g1m_mcshead_flags |= g1m_mcsflag_unfinished;
		end = memchr(hd.aux, 0xFF, 8);
		len = end ? (size_t)(end - (char*)hd.aux) : 8;
		memcpy(head->g1m_mcshead_password, hd.aux, len);
		head->g1m_mcshead_password[len] = 0;
		log_info("Is a program of %" PRIuFAST32 " bytes",
			head->g1m_mcshead_size);
		break;
	case g1m_mcstype_variable:
	case g1m_mcstype_matrix:
	case g1m_mcstype_list:
		head->g1m_mcshead_height = be16toh(hd.height) & 0xFF;
		head->g1m_mcshead_width = be16toh(hd.width) & 0xFF;
		head->g1m_mcshead_count = head->g1m_mcshead_height;
		if (head->g1m_mcshead_width && head->g1m_mcshead_height)
			head->g1m_mcshead_flags |= g1m_mcsflag_unfinished;
		break;
	}

	/* TODO */
	return (0);
}

/**
 *	g1m_decode_casfile_head:
 *	Decode the CAS file head.
 *
 *	@arg	head		the head to decode.
 *	@arg	buffer		the buffer to read the header from.
 *	@return				the error code (0 if ok).
 */

int g1m_decode_casfile_head(g1m_mcshead_t *head, g1m_buffer_t *buffer)
{
	/* check that the head exists */
	if (!head) return (-1);
	memset(head, 0, sizeof(g1m_mcshead_t));

	/* read beginning of the header, check if is an extended header */
	uint8_t buf[39]; READ(buf, 4)
	uint8_t csum = g1m_checksum8(buf, 4);
	struct casdyn *dhd = (void*)buf;
	if (!g1m_maketype_casapp(head, dhd->ext, (char*)dhd->app))
	  switch (head->g1m_mcshead_info) {
		case g1m_mcsinfo_cas50:  return (decode_cas50(head, buffer, csum));
		//case g1m_mcsinfo_cas100: return (decode_cas100(head, buffer));
		default:
			log_error("Platform 0x%04X isn't implemented yet.",
				head->g1m_mcshead_info);
			return (g1m_error_op);
	}

	/* is a CAS40 head, read it. */
	READ(&buf[4], 35) struct cas40 *hd = (void*)buf;
	csum += g1m_checksum8(&buf[4], 34);
	log_info("Raw CAS40 (CAS) header:");
	logm_info(hd, sizeof(struct cas40));
	if (g1m_maketype_cas(head, (char*)hd->data))
		return (g1m_error_unrecognized);
	if (~csum + 1 != hd->checksum)
		return (g1m_error_checksum);

	/* fill the handle */
	memset(head, 0, sizeof(g1m_mcshead_t));
	head->g1m_mcshead_info = g1m_mcsinfo_cas40;
	memcpy(head->g1m_mcshead_name, hd->filename, 12);
	head->g1m_mcshead_name[12] = 0;

	/* type specific things */
	if (head->g1m_mcshead_type == g1m_mcstype_program) {
		struct cas_spe_program *spe = (void*)hd->misc;
		head->g1m_mcshead_size = be16toh(spe->length);
		/* TODO: store flags? */
	}

	/* no error! */
	return (0);
}
/* ************************************************************************** */
/*  Part decoding functions                                                   */
/* ************************************************************************** */
/**
 *	g1m_decode_casfile_part:
 *	Decode a CASIOLINK Protocol content part.
 *
 *	@arg	file	the file to contribute to.
 *	@arg	buffer	the buffer to read from.
 *	@return			if there was an error, or not.
 */

int g1m_decode_casfile_part(g1m_mcsfile_t *file, g1m_buffer_t *buffer)
{
	/* checks */
	if (!file) return (g1m_error_op);

	/* look for the decoding function */
	cas_decode_function decode = (void*)lookup_cas_decode(
		file->g1m_mcsfile_head.g1m_mcshead_type, 0);
	if (!decode) {
		log_error("No dedicated decoding function was found for this type!");
		return (g1m_error_unknown);
	}

	/* decode the part */
	return ((*decode)(file, buffer));
}
/* ************************************************************************** */
/*  Main file decoding function                                               */
/* ************************************************************************** */
#define READGSIZE() if (grc) { \
	uint16_t size; READ(&size, 2) \
	log_info("GraphCard next buffer size was: 0x%04X", be16toh(size)); }
#define READCOLON() { \
	READGSIZE() \
	uint8_t colon; GREAD(&colon, 1) \
	err = g1m_error_magic; \
	if (colon != ':') { \
		log_error("Expected ':', got '%c' (0x%02X)", colon, colon); \
		goto fail; \
	}}

/**
 *	decode_cas:
 *	Decode a CAS file.
 *
 *	Is also sort of a guide for using the CAS MCS files.
 *	The colon ':' (0x3A) is already read at this point (CAS file id.).
 *
 *	@arg	h		the handle to create.
 *	@arg	buffer	the buffer to read from.
 *	@arg	grc		is a graphcard file.
 *	@return			the libg1m error.
 */

static int decode_cas(g1m_handle_t **h, g1m_buffer_t *buffer, int grc)
{
	/* make the handle */
	int err = g1m_make_mcs(h, 0);
	if (err) return (err);
	g1m_handle_t *handle = *h;

	/* read each */
	for (handle->g1m_handle_count = 0;;) {
		/* read the head */
		log_info("Reading the next head.");
		g1m_mcshead_t head = {};
		if ((err = g1m_decode_casfile_head(&head, buffer))) goto fail;
		if (head.g1m_mcshead_type == g1m_mcstype_end) break;

		/* prepare the file */
		log_info("Preparing the file.");
		g1m_mcsfile_t *file; err = g1m_mcs_insert(handle, &file, &head);
		if (err) goto fail;

		/* read each part */
#if LOGLEVEL <= ll_info
		for (int j = 1; file->g1m_mcsfile_head.g1m_mcshead_flags
		   & g1m_mcsflag_unfinished; j++) {
#else
		while (file->g1m_mcsfile_head.g1m_mcshead_flags
		   & g1m_mcsflag_unfinished) {
#endif
			/* initialize */
			log_info("Reading part #%d", j);
			READCOLON()

			/* read the part */
			err = g1m_decode_casfile_part(file, buffer);
			if (err) goto fail;
		}

		/* read first colon of the next part */
		READCOLON()
	}

	/* read last size (check if zero?) */
	READGSIZE()

	/* everything went well :) */
	return (0);

fail:
	/* END OF DA WORLD */
	g1m_free(handle);
	return (err);
}

/* ************************************************************************** */
/*  Public decoding functions                                                 */
/* ************************************************************************** */
/**
 *	g1m_decode_cas:
 *	Decode a CAS file.
 *
 *	@arg	handle	the handle to make.
 *	@arg	buffer	the buffer to read from.
 *	@return			the libg1m error.
 */

int g1m_decode_cas(g1m_handle_t **handle, g1m_buffer_t *buffer)
{
	return (decode_cas(handle, buffer, 0));
}

/**
 *	g1m_decode_grc:
 *	Decode Graph Card file.
 *
 *	@arg	handle		the handle to make.
 *	@arg	buffer		the buffer to read from.
 *	@return				the error code (0 if ok).
 */

int g1m_decode_grc(g1m_handle_t **handle, g1m_buffer_t *buffer)
{
	return (decode_cas(handle, buffer, 1));
}