/* McPhail's Tip-Top TAP Top-Tailer
 * Takes a raw code file as input
 * Prepends data length and appends xor checksum
 * Outputs to new file with .block suffix */


#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <linux/limits.h>
#include <string.h>

int main(int argc, char *argv[])
{
	int fdin, fdout;
	char outfilename[PATH_MAX];
	unsigned int count = 0;
	unsigned char tally = 0;
	unsigned char next = 0;
	if (argc!=2) {
		printf("Please specify file to read.\n");
		return -1;
	}

	fdin = open(argv[1], O_RDONLY);
	if (fdin<0) {
		printf("Couldn't open %s. for reading\n", argv[1]);
		return -1;
	}

	snprintf(outfilename, PATH_MAX, "%s.block", argv[1]);
	outfilename[PATH_MAX - 1] = '\0';
	if (! strcmp(argv[1], outfilename)) {
		printf("Filename too long - would clobber existing.\n");
		close(fdin);
		return -1;
	}

	fdout = open(outfilename, O_CREAT|O_WRONLY|O_TRUNC, S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH);
	if (fdout<0) {
		printf("Couldn't open %s for writing.\n", outfilename);
		close(fdin);
		return -1;
	}

	while (read(fdin, &next, 1)) {
		tally ^= next;
		count ++;
	};
	lseek(fdin, 0, SEEK_SET);

	char lsb = (count+1)&255;
	char msb = ((count+1)>>8)&255;
	write(fdout, &lsb, 1);
	write(fdout, &msb, 1);
	while (read(fdin, &next, 1)) {
		write(fdout, &next, 1);
	}
	write(fdout, &tally, 1);

	close(fdout);
	close(fdin);

	printf("File %s written.\n", outfilename);
	printf("Code length including first byte is %d (0x%.4X).\n", count, count);
	printf("Removing first byte gives 0x%.4X.\n", count-1);

	return 0;
}