/*

Hide - A little tool to hide data in image files from noobs
Copyright (C) 2007 Lars Stoltenow <penma@penma.de>

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 2 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, write to the Free Software Foundation, Inc., 51 Franklin
St, Fifth Floor, Boston, MA 02110, USA

*/
#include <stdio.h>

void usage()
{
	// FIXME: Replace with some getopts calls, same with argument parser.
	fprintf(stderr,
		"Usage:\n"
		"\thide [ <options> ] <srcfile> <destfile>\n"
		"\thide [ <options> ] <srcfile>\n"
		"\n"
		"<srcfile> specifies the file that's to be embedded in <destfile>, or\n"
		"the file where embedded data should be extracted from.\n"
		"\n"
		"Available options:\n"
		"\t--help or -h or -?   Show this help message.\n"
	);
}

int hide(FILE *srcfile, FILE *destfile, FILE *outfile)
{
	unsigned char srcbyte, destbytes[4];
	
	// Read bytes from destination file until the end is reached.
	do
	{
		// Check if the source file has still bytes to offer, if not, include
		// null bytes (I think they always fit). :)
		if (feof(srcfile))
		{
			srcbyte = 0x00;
		}
		else
		{
			fread(&srcbyte, 1, 1, srcfile);
		}
		
		// Read 4 bytes from the destination file to include the data there.
		fread(destbytes, 1, 4, destfile);
		
		// Empty the lower 2 bits.
		destbytes[0] &= 0xfc;
		destbytes[1] &= 0xfc;
		destbytes[2] &= 0xfc;
		destbytes[3] &= 0xfc;
		
		// Include the bits from the source file.
		destbytes[0] += (srcbyte >> 0) & 0x03;
		destbytes[1] += (srcbyte >> 2) & 0x03;
		destbytes[2] += (srcbyte >> 4) & 0x03;
		destbytes[3] += (srcbyte >> 6) & 0x03;
		
		// Write out the new data.
		fprintf(outfile, "%c%c%c%c", destbytes[0], destbytes[1], destbytes[2], destbytes[3]);
	} while (!feof(destfile));
	
	// Make sure the files are closed! The calling unction won't do this.
	fclose(srcfile);
	fclose(destfile);
	
	return 0;
}

int unhide(FILE *srcfile, FILE *outfile)
{
	unsigned char srcbytes[4];
	
	// Go through the file and push bits to the output.
	do
	{
		// Get new bytes!
		fread(srcbytes, 1, 4, srcfile);
		
		// And write them to the output!
		fprintf(outfile, "%c", (srcbytes[0] & 0x03) | ((srcbytes[1] & 0x03) << 2) | ((srcbytes[2] & 0x03) << 4) | ((srcbytes[3] & 0x03) << 6));
	} while (!feof(srcfile));
	
	// Make sure the file gets closed! The calling routine won't do this for us.
	fclose(srcfile);
	
	return 0;
}

int main(int argc, char *argv[])
{
	FILE *srcfile, *destfile;
	
	if ((argc == 2) && (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h") || !strcmp(argv[1], "-?")))
	{
		usage();
		return 0;
	}
	
	if (argc == 3)
	{
		// Assume there are two filenames specifying the source and destination
		// file.
		srcfile = fopen(argv[1], "r");
		if (srcfile == NULL)
		{
			perror("hide: Error opening source file");
			return 1;
		}
		
		destfile = fopen(argv[2], "r");
		if (destfile == NULL)
		{
			perror("hide: Error opening destination file");
			fclose(srcfile);
			return 1;
		}
		
		// Output to the output file. (It's stdout for now.)
		return hide(srcfile, destfile, stdout);
	}
	
	if (argc == 2)
	{
		// Assume there is one filename specifying tzhe file to be decoded.
		srcfile = fopen(argv[1], "r");
		if (srcfile == NULL)
		{
			perror("hide: Error opening source file");
			return 1;
		}
		
		// Dump the hidden file to the output file. (It's stdout for now.)
		return unhide(srcfile, stdout);
	}
	
	// Reaching here mostly means argument errors. Yell it out to the poor user!
	fprintf(stderr, "hide: Not enough arguments\n");
	fprintf(stderr, "Use the '--help' option to get a list of available options.\n");
	return 1;
}