/******************************************************************************
 * 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.
 *****************************************************************************/

import org.pureprogrammer.Utils;

public class VigenereCipher {

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

    static int shiftChar(int cp, int shift, boolean encrypt) {
        int newCp = cp;
        int pos = Utils.cpIndexOf(ALPHABET, cp);
        if (pos != -1) {
            if (encrypt) {
                pos = (pos + shift) % ALPHABET_LEN;
            } else {
                pos = (pos - shift + ALPHABET_LEN) % ALPHABET_LEN;
            }
            newCp = Utils.cpAt(ALPHABET, pos);
        }
        return newCp;
    }

    public static void main(String[] args) {
        if (args.length != 2) {
            System.out.println(Utils.join("", "Syntax: ", "VigenereCipher", " password e|d"));
            System.exit(1);
        }
        String password = args[0];
        boolean encrypt = (args[1].equals("e") );
        int passwordPos = 0;
        int passwordLen = Utils.cpLength(password);

        int c;
        while ((c = Utils.getchar()) != -1) {
            int pwdCp = Utils.cpAt(password, passwordPos % passwordLen);
            int shift = Utils.cpIndexOf(ALPHABET, pwdCp);
            if (shift != -1) {
                c = shiftChar(c, shift, encrypt);
            }
            System.out.print(String.valueOf(Character.toChars(c)));
            ++passwordPos;
        }
    }
}