#include <iostream>
#include <string>
#include <limits.h>
#include <fstream>



void CheckAsciiPos(short& pos) {
    if (std::numeric_limits<char>::is_signed) {
        if (pos > 127) //if it leaves ascii table :)
            pos -= 256;
        if (pos < -128)
            pos += 256;
    }
    else {
        if (pos > 255) //if it leaves ascii table :)
            pos -= 256;
        if (pos < 0)
            pos += 256;
    }
}



//((P XOR((K + KC) XOR K)) + ((K + KC) XOR K))
std::string encrypt(std::string plaintext, std::string password) {

    int passPos = 0;
    short asciiPosCipher;
    short passCounter = 1;
    short asciiPosPass;
    std::string cipher;

    for (unsigned int i = 0; i < plaintext.length(); i++) { //do for every character in string

        if (passPos >= password.length()) //after password ends start
            passPos = 0; //start from the beginning
        if (passCounter > 255)
            passCounter = 0;
        asciiPosPass = (password[passPos] + passCounter); //shift password char around passCounter
        CheckAsciiPos(asciiPosPass); //checks and corrects position pos in asciitable
        asciiPosPass ^= password[passPos]; //xor shifted password char with original password char
        asciiPosCipher = plaintext[i] ^ asciiPosPass; //xor this with plaintext char
        asciiPosCipher += asciiPosPass; //shift both to result
        CheckAsciiPos(asciiPosCipher);
        cipher += static_cast<char>(asciiPosCipher); //cast them to char an add to cipher-text
        passPos++; //next char in password
        passCounter++;
    }

    return cipher;
}


//((C - ((K + KC) XOR K)) XOR ((K + KC) XOR K))
std::string decrypt(std::string cipher, std::string password) {

    int passPos = 0;
    short asciiPosResult;
    short passCounter = 1;
    short asciiPosPass;
    std::string result;

    for (unsigned int i = 0; i < cipher.length(); i++) {

        if (passPos >= password.length())
            passPos = 0;
        if (passCounter > 255)
            passCounter = 0;
        asciiPosPass = (password[passPos] + passCounter);
        CheckAsciiPos(asciiPosPass);
        asciiPosPass ^= password[passPos];
        asciiPosResult = cipher[i] - asciiPosPass;
        asciiPosResult ^= asciiPosPass;
        CheckAsciiPos(asciiPosResult);
        result += static_cast<char>(asciiPosResult);
        passPos++;
        passCounter++;
    }

    return result;
}



int main() {

    std::string fileName = "test.exe";
    std::ifstream input(fileName, std::ios::binary);

    std::string plaintext;

    char byte;
    while (input.get(byte)) {
        plaintext += byte;
    }


    std::string password = "testpass";
    std::string cipher;
    std::string result;

    cipher = encrypt(plaintext, password);

    std::ofstream enc("test_enc.exe", std::ios::app | std::ios::binary);
    enc << cipher;
    enc.close();

    result = decrypt(cipher, password);

    std::ofstream dec("test_dec.exe", std::ios::app | std::ios::binary);
    dec << result;
    dec.close();


    std::cin.get();
    return 0;
}