#include <iostream>
#include <string>
#include <fstream>
#include <streambuf>
#include <math.h>
#include <vector>

#define varName(x) (#x)

using namespace std;

bool isPrime(int);

int calcE(int);
int gcd(int, int);
int calcD(int, int);

int encryption(int, int, int);
int decryption(int, int, int);

template <class... Ts>
void writeResult(ofstream &file, Ts const&... args);

int main() {
    //Method data
    int p, q, n, t, e, d;
    bool primeFlag;

    string msg;
    string encryptedText;
    string decryptedText;

    ifstream textFile, valuesFile;

    //Opening input files
    valuesFile.open("TP_92_Gorokhovska_mkr2.dat");
    textFile.open("TP_92_Gorokhovska_mkr2.rsa");

    //Input p and q values
    if (!valuesFile.is_open()) {
        //cout << "Error!! There are not such .dat file!!" << endl;
        cout << "Enter prime values for p and q: " << endl;

        //Input p value
        cout << "p: ";
        do {
            cin >> p;

            if (!isPrime(p)) {
                cout << "Wrong input!! This number is not Prime!" << endl;
                cout << "Try again: ";
            }
        } while (!isPrime(p));

        //Input q value
        cout << "q: ";
        do {
            cin >> q;

            if (!isPrime(q)) {
                cout << "Wrong input!! This number is not Prime!" << endl;
                cout << "Try again: ";
            }
        } while (!isPrime(q));
    }
    else {
        cout << "Reading .dat file..." << endl;
        valuesFile >> p;
        valuesFile >> q;
        cout << "Reading complete!" << endl;
        cout << "Data from file: " << endl << endl;
        cout << "p: " << p << endl;
        cout << "q: " << q << endl;
    }

    //Input coding text
    if (!textFile.is_open()) {
        //cout << "Error!! There are not such .rsa file!!" << endl;
        cout << "Enter coding text: ";
        cin >> msg;
    }
    else {
        cout << "Reading .rsa file..." << endl;
        textFile >> msg;
        cout << "Reading complete!" << endl;
        cout << "Data from file: " << endl;
        cout << "Text: " << msg << endl;
    }

    //Calculate modulus - n
    n = p * q;
    cout << "\nn: " << n << endl;

    //Calculate Euler totient function - t
    t = (p - 1)*(q - 1);
    cout << "t: " << t << endl << endl;

    //Calculation of the open exponent - e
    e = calcE(t);

    //Calculation of the hidden exponent - d
    d = calcD(e, t);

    //Public RSA key
    cout << "Public RSA key: [e = " << e << ", n = " << n << "]" << endl;

    //Private RSA key
    cout << "Private RSA key: [d = " << d << ", n = " << n << "]" << endl << endl;

    //Encryption
    for (int i = 0; i < msg.length(); i++) {
        encryptedText += (char)encryption(msg[i], e, n);
    }

    //Decryption
    for (int i = 0; i < msg.length(); i++) {
        decryptedText += (char)decryption(encryptedText[i], d, n);
    }

    //Result
    cout << "Encrypted message: " << encryptedText << endl;
    cout << "Decrypted message: " << decryptedText << endl;

    //Output info to file
    ofstream outFile("TP_92_Gorokhovska_mkr2.txt");
    writeResult(outFile, p, q, n, t, e, d, encryptedText, decryptedText);


    system("pause");
    return 0;
}

//Check for prime number
bool isPrime(int num) {
    int j = sqrt((double)num);

    for (int i = 2; i <= j; i++) {
        if (num % i == 0) {
            return false;
        }
    }

    return true;
}

//Calculation of the open exponent - e
int calcE(int t) {
    for (int e = 2; e < t; e++) {
        if (gcd(e, t) == 1) return e;
    }
    return -1;
}

int gcd(int e, int t) {
    int temp;
    while (e > 0) {
        temp = e;
        e = t % e;
        t = temp;
    }
    return t;
}

//Calculation of the hidden exponent - d
int calcD(int e, int t) {
    int d;
    int k = 1;

    while (true) {
        k += t;

        if (k%e == 0) {
            d = k / e;
            return d;
        }
    }
}

//Encryption
int encryption(int symbol, int e, int n) {
    int current, result;

    current = symbol - 97;
    result = 1;

    for (int i = 0; i < e; i++) {
        result *= current;
        result %= n;
    }

    return result;
}

//Decryption
int decryption(int symbol, int d, int n) {
    int current, result;

    current = symbol;
    result = 1;

    for (int i = 0; i < d; i++) {
        result *= current;
        result %= n;
    }

    return result + 97;
}

//Write all info to file
template <class T, class... Ts>
void writeResult(ofstream &file, T const& first, Ts const&... args) {
    /*using expander = int[];
    (void)expander {
        0, (void(file << args), 0)...
    };*/

    file << varName(first) << ": " << first << endl;

    if constexpr (sizeof...(args) > 0) writeResult(file, args...);
}