//
// Author: Danny Loffredo
// dgl4b@virginia.edu
//
// Version 1.0 - 29 August 3:54PM
//
// usage: 
//
//      a.out <ciphertext1> <ciphertext2> <messageguess>
// 
// <ciphertext1> and <ciphertext2> are the names of files containing ciphertexts at 0 and 1's (as
//   in the c1.txt and c2.txt
//
// <messageguess> is a plain text file for the message guess.
//
// The output is the plaintext corresponding to <ciphertext2>, if <messageguess> is the message
// that <ciphertext1> encodes.
//
// Non-printable characters appear as '$'.
//

// C1 = M1 xor K
// C2 = M2 xor K
// C' = C1 xor C2 = M1 xor M2
// M2 = C' xor M1

#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <ctype.h>
using namespace std;

typedef char              SevenBits;
typedef vector<SevenBits> Bits;

Bits   StringToBits    ( string ascii_string );
Bits   BitStringToBits ( string bit_string );
string BitsToString    ( Bits the_bits );
Bits   XorBits         ( Bits a, Bits b );

Bits   XorBits         ( Bits a, Bits b )
{
	Bits answer;

	int smallest;
	if ( a.size() < b.size() )
		smallest = a.size();
	else
		smallest = b.size();

	for(int index = 0; index < smallest; index++)
	{
		int a_int = int( a[index] );
		int b_int = int( b[index] );
		int next = (a_int ^ b_int) & 127;
		answer.push_back( char(next) );
	}

	return answer;
}

string BitsToString    ( Bits the_bits )
{
	string answer;
	answer.resize( the_bits.size() );

	for(int index = 0; index < the_bits.size(); index++)
	{

	  if (the_bits[index] == 0)
	    answer[index] = '$';
	  else
	    answer[index] = the_bits[index];

	  if (!isprint (answer[index]))
	    {
	      answer[index] = '$';
	    }
	}

	return answer;
}

Bits   StringToBits    ( string ascii_string )
{
	Bits answer;
	answer.resize( ascii_string.size() );
	
	for(int index = 0; index < ascii_string.size(); index++)
	{
		answer[index] = ascii_string[index];
	}

	return answer;
}

Bits   BitStringToBits ( string bit_string )
{
	Bits answer;

	if ( bit_string.size() % 7 != 0 )
		return answer;

	answer.resize( bit_string.size() / 7 );

	for(int index = 0; index < answer.size(); index++)
	{
		int number = 0;

		for(int count = 0; count < 7; count++)
		{
			char this_bit = bit_string[index * 7 + count];
			switch(this_bit)
			{
			case '0':
				number = 2 * number;
				break;
			case '1':
				number = 2 * number + 1;
				break;
			}
		}

		answer[index] = char(number);
	}
	return answer;
}

int main(int argc, char* argv[])
{
	if(argc < 4)
	{
		cout << "Usage: " << string(argv[0]) << " <cipher1> <cipher2> <message1 guess>" << endl;
		return 1;
	}
	else
	{
		ifstream Cipher1Stream;
		ifstream Cipher2Stream;
		ifstream Message1Stream;

		Cipher1Stream.open(argv[1], ios::in);
		Cipher2Stream.open(argv[2], ios::in);
		Message1Stream.open(argv[3], ios::in);

		string C1Input;
		string C2Input;
		string M1Input;

		Cipher1Stream >> C1Input;
		Cipher2Stream >> C2Input;
		
		Message1Stream >> M1Input;
		string input;
		int ic;

		while ((ic = Message1Stream.get ()) != EOF)
		  M1Input = M1Input + char (ic);

		Bits Cipher1 = BitStringToBits(C1Input);
		Bits Cipher2 = BitStringToBits(C2Input);
		Bits Message1 = StringToBits(M1Input);

		Bits CipherPrime = XorBits(Cipher1, Cipher2);
		Bits Message2 = XorBits(CipherPrime, Message1);

		cout << BitsToString(Message2) << endl;
		return 0;
	}

}