/******************************************************/
/* This program will encrypt and decrypt messages. The*/
/* user will simply have to remeber a secret key.     */
/******************************************************/
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

// Function Prototypes ---------------------------------
int GetUserChoice ();

void Encryption ();
void Decryption ();

string XorString ( string source, int key );
// -----------------------------------------------------

// Main Function ---------------------------------------
int main ()
{
	
	// Variable to hold our choice
	int choice;
	
	// Create an infinite loop -------------------------
	while ( 1 ) {
		
		// GetUserChoice will return what the user wants to do
		// We can assign the returned value to our variable
		choice = GetUserChoice ();
		
		// Now we can check what the user wants
		if ( choice == 1 ) Encryption ();
		else if ( choice == 2 ) Decryption ();
		
		// If the choice was 3 that means we can break from our loop
		else if ( choice == 3 ) break;
		
	}
	// -------------------------------------------------
		
	return 0;
	
}

// GetUserChoice Function ------------------------------
int GetUserChoice ()
{
	
	// Variable for the choice
	int choice;
	
	// Here we will print our menu and prompt for a number
	// This number will represent what the user wants to do
	// Once we have the number this function will return it
	cout << "Message Encryption" << endl;
	cout << "----------------------" << endl;
	cout << "1) Encrypt Message" << endl;
	cout << "2) Decrypt Message" << endl;
	cout << "3) Exit" << endl << endl;
	cout << "Make a selection: ";
	cin  >> choice;
	
	// Now we will check to make sure the choice was valid
	if ( choice != 1 && choice != 2 && choice != 3 ) {
		
		cout << endl;
		cout << "Please enter 1, 2, or 3" << endl;
		cout << "Press enter to exit...";
		
		// Since the user entered an invalid selection we
		// will just exit the program by returning our programs
		// exit code.. 3
		
		cin.get ();
		return 3;
		
	}
	
	// If it makes it to this point that means the input was valid so we can return it
	return choice;
	
}
// -----------------------------------------------------

// Here is where we will encrypt the string ------------
string XorString ( string source, int key )
{
	
	// Here we loop through each character, using binary xor on it.
	for ( unsigned int loop = 0; loop < source.size (); loop ++ ) {
		
		source [loop] ^= key;
		
	}
	
	return source;
	
}

// Here we will get the file name, key, and message from the user ----
void Encryption ()
{
	
	// Variables for the file name, key and message ----
	char file_name [255];
	
	string message;
	string encrypted_message;
	
	int key;
	// -------------------------------------------------
	
	cout << endl;
	cout << "Enter file name: ";
	cin  >> file_name;
	
	cout << "Enter secret key: ";
	cin  >> key;
	
	cout << "Enter your secret message." << endl;
	cout << "Message: ";
	
	// We need this to ignore anything that might be left over
	// and ruin our message
	cin.ignore ( 255, '\n' );
	
	getline ( cin, message );
	
	// Now we have all of the info we can encrypt and write --
	// the string to the file --------------------------------
	encrypted_message = XorString ( message, key );
	
	ofstream file ( file_name );
	
	file << encrypted_message;
	
	file.close ();
	// -------------------------------------------------------
	
	cout << "Done..." << endl << endl;
	
}
// -------------------------------------------------------------------

// Decryption will work the same way. Instead of asking the user for the message, --- 
// we print it out. -----------------------------------------------------------------
void Decryption ()
{
	
	// Variables for the file name, key and message ----
	char file_name [255];
	
	string message;
	
	int key;
	// -------------------------------------------------
	
	cout << endl;
	cout << "Enter file name: ";
	cin  >> file_name;
	
	cout << "Enter secret key: ";
	cin  >> key;
	
	// Now we will check to see if the file exists -----
	ifstream file ( file_name );
	
	if ( !file.is_open () ) {
		
		cout << "Failed to load " << file_name << "!" << endl;
		cout << "Press enter to exit...";
		
		cin.get ();
		
		exit ( EXIT_FAILURE );
		
	}
	// -----------------------------------------------
	
	getline ( file, message );
	
	file.close ();
	
	cout << "Message: " << XorString ( message, key ) << endl;
	
	cout << "Done..." << endl << endl;
	
}