/******************************************************************************
 * This filter program encrypts/decrypts text using a Vigenere Cipher.
 * Input text is taken from standard input and output text is written
 * to standard output.  Assume only ASCII input/output.
 * 
 * The first command line argument is the password
 * The second command line argument is the encrypt "e" or decrypt "d"
 * mode.
 * 
 * Copyright © 2017 Richard Lesh.  All rights reserved.
 *****************************************************************************/

#undef NDEBUG

#include "Utils.hpp"
#include <clocale>
#include <codecvt>
#include <iostream>
#include <string>

std::locale utf8loc(std::locale(), new std::codecvt_utf8<wchar_t>);
using namespace std;

static wstring const ALPHABET = L" !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~";
static int const ALPHABET_LEN = ALPHABET.length();

int shift_char(int cp, int shift, bool encrypt) noexcept {
    int new_cp = cp;
    int pos = ALPHABET.find(cp);
    if (pos != string::npos) {
        if (encrypt) {
            pos = (pos + shift) % ALPHABET_LEN;
        } else {
            pos = (pos - shift + ALPHABET_LEN) % ALPHABET_LEN;
        }
        new_cp = (int)(ALPHABET[pos]);
    }
    return new_cp;
}

int main(int argc, char **argv) {
    setlocale(LC_ALL, "en_US.UTF-8");
    wcout.imbue(utf8loc);
    wcin.imbue(utf8loc);

    if (argc != 3) {
        wcout << L"Syntax: " << Utils::UTF8_to_wstring(argv[0]) << L" password e|d" << endl;
        exit(1);
    }
    wstring password = Utils::UTF8_to_wstring(argv[1]);
    bool encrypt = (Utils::UTF8_to_wstring(argv[2]) == L"e");
    int password_pos = 0;
    int password_len = password.length();

    int c;
    while ((c = getwchar()) != EOF) {
        int pwd_cp = (int)(password[password_pos % password_len]);
        int shift = ALPHABET.find(pwd_cp);
        if (shift != string::npos) {
            c = shift_char(c, shift, encrypt);
        }
        putwchar(c);
        ++password_pos;
    }
    return 0;
}