/*    
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program 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 General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdio.h>
#include <string.h>
#include "crc-itu-t.h"
#include "dvdv.h"

#define LBA_SIZE 2048

int main(int argc, char ** argv) {
	FILE *iso;
	unsigned char buffer[LBA_SIZE], tag_checksum;
	unsigned short i, is_udf = 0;
	unsigned short *desc_crc;
	unsigned short *desc_crc_len;

	printf("ESRPATCH v0.2 - PS2 ISO patcher for ffgriever's ESR project.\n");
	printf("By: bootsector - http://www.brunofreitas.com/\n\n");

	if(argc != 2) {
		printf("Usage: esrpatch <path_to_iso>\n");
		return 1;
	}

	if((iso = fopen(argv[1], "rb+")) == NULL) {
		printf("Error opening ISO.\n");
		return 1;
	}

	memset(buffer, 0, sizeof(buffer));

	// Checks if ISO has an UDF descriptor
	for(i = 1; i < 64; i++) {
		fseek(iso, LBA_SIZE * i + 32768, SEEK_SET);
		fread(buffer, LBA_SIZE, 1, iso);

		// "NSR"
		if(!strncmp(buffer + 1, "NSR", 3)) {
			is_udf = 1;
			break;
		}
	}

	if(!is_udf) {
		printf("Error: ISO doesn't contain an UDF descriptor.\n");
		fclose(iso);
		return 1;
	}

	// Checks if image is already patched
	fseek(iso, 14 * LBA_SIZE, SEEK_SET);
	fread(buffer, LBA_SIZE, 1, iso);

	if(!strncmp(buffer + 25, "+NSR", 4)) {
		printf("ISO is already patched.\n");
		fclose(iso);
		return 1;
	}

	// Backups LBA 34 into 14
	fseek(iso, 34 * LBA_SIZE, SEEK_SET);
	fread(buffer, LBA_SIZE, 1, iso);

	fseek(iso, 14 * LBA_SIZE, SEEK_SET);
	fwrite(buffer, LBA_SIZE, 1, iso);

	// Backups LBA 50 into 15
	fseek(iso, 50 * LBA_SIZE, SEEK_SET);
	fread(buffer, LBA_SIZE, 1, iso);

	fseek(iso, 15 * LBA_SIZE, SEEK_SET);
	fwrite(buffer, LBA_SIZE, 1, iso);

	// Updates LBA 34
	fseek(iso, 34 * LBA_SIZE, SEEK_SET);
	fread(buffer, LBA_SIZE, 1, iso);

	// Updates new referenced LBA: Now it points to a DVD_VIDEO structure
	buffer[0xBC] = 0x80;
	buffer[0xBD] = 0x00;

	// Calculates new checksums
	desc_crc_len = (unsigned short *)(buffer + 10);	
	desc_crc = (unsigned short *)(buffer + 8);

	*desc_crc = crc_itu_t(0, (buffer + 16), *desc_crc_len);

	tag_checksum = 0;

	for(i = 0; i < 4; i++)
		tag_checksum += buffer[i];

	for(i = 5; i < 16; i++)
		tag_checksum += buffer[i];

	buffer[4] = tag_checksum;

	// Save modified LBA
	fseek(iso, 34 * LBA_SIZE, SEEK_SET);
	fwrite(buffer, LBA_SIZE, 1, iso);

	// Updates LBA 50
	fseek(iso, 50 * LBA_SIZE, SEEK_SET);
	fread(buffer, LBA_SIZE, 1, iso);

	// Updates new referenced LBA: Now it points to a DVD_VIDEO structure
	buffer[0xBC] = 0x80;
	buffer[0xBD] = 0x00;

	desc_crc_len = (unsigned short *)(buffer + 10);	
	desc_crc = (unsigned short *)(buffer + 8);

	*desc_crc = crc_itu_t(0, (buffer + 16), *desc_crc_len);

	// Calculates new checksums
	tag_checksum = 0;

	for(i = 0; i < 4; i++)
		tag_checksum += buffer[i];

	for(i = 5; i < 16; i++)
		tag_checksum += buffer[i];

	buffer[4] = tag_checksum;

	// Save modified LBA
	fseek(iso, 50 * LBA_SIZE, SEEK_SET);
	fwrite(buffer, LBA_SIZE, 1, iso);

	// Writes DVD Video data @ LBA 128
	fseek(iso, 128 * LBA_SIZE, SEEK_SET);
	fwrite(dvdvdata, DVDVDATA_SIZE, 1, iso);

	fclose(iso);

	printf("Done!\n");

	return 0;
}