/*
 * JR-IDE Project
 * - (c) 2020 Alan Hightower
 *
 * 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 <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>


#define LOGERR(fmt, args...) \
        fprintf (stderr, "\nERROR: " fmt "\n\n", ## args)

int main (int argc, char *argv[])
{
	if (argc < 2)
	{
		fprintf (stderr, "\nUsage: %s <bios_image>\n\n", argv[0]);

		return -1;
	}

	int sts = -1, fd = -1;

	struct stat st_info;

	uint8_t *buffer = NULL;

	do
	{
		if (stat (argv[1], &st_info))
		{
			LOGERR("Unable to stat '%s' - %s",
			       argv[1], strerror (errno));
			break;
		}

		if ((fd = open (argv[1], O_RDWR)) < 0)
		{
			LOGERR("Unable to open '%s' - %s",
			       argv[1], strerror (errno));
			break;
		}

		if (!(buffer = (uint8_t *) malloc (st_info.st_size)))
		{
			LOGERR("Unable to allocate %ld bytes - %s",
			       st_info.st_size, strerror (errno));
			break;
		}

		size_t len = read (fd, buffer, st_info.st_size);

		if (len != (size_t) st_info.st_size)
		{
			LOGERR("Unable to read %ld bytes (%ld) - %s",
			       st_info.st_size, (unsigned long) len, strerror (errno));
			break;
		}

		int i;

		uint8_t sum = 0;

		for (i = 0; i < (int) len; i++)
			sum += buffer[i];

		if (!sum)
		{
			printf ("File '%s' already checksum'd to zero\n", argv[1]);

			sts = 0;

			break;
		}

		if (lseek (fd, len - 1, SEEK_SET) != (off_t) (len - 1))
		{
			LOGERR("Unable to seek to end of file - %s",
			       strerror (errno));
			break;
		}

		sum -= buffer[len - 1];
		sum  = 0x100 - (int) sum;

		if (write (fd, &sum, 1) != 1)
		{
			LOGERR("Unable to write checksum - %s",
			       strerror (errno));
			break;
		}

		printf (" -CSUM-   Checksum Fix-up \'%s\' (0x%02x)\n",
		        argv[1], sum);

		sts = 0;

	} while (0);

	if (fd >= 0)
		close (fd);

	if (buffer)
		free (buffer);

	return sts;
}