canyoucrackit.js

function toLetter(number = 0) {
  return String.fromCharCode(number%26+65)
}

function toNumber(string = 'A', index = 0) {
  return string.charCodeAt(index)-65
}

function encryptLetter(message='', key='', index=0) {
  return toLetter(
    toNumber(message,index)
    +toNumber(key,index%key.length)
    %26
  );
}

function shuffle(message='', shufflestring='ABCDEFGHIJKLMNOPQRSTUVWXYZ') {
  return message
    // transform message into array
    .split('') 
    // do the shuffle operation for every letter
    .map(letter => shufflestring[
        (shufflestring.indexOf(letter)+1)%shufflestring.length
      ]
    )
    // transform the message back into a string
    .join('')
}

function encrypt(message='', key='', shufflestring='ABCDEFGHIJKLMNOPQRSTUVWXYZ') {
  let charcode = 0;
  let shift = 0;
  let sliceindex = 0;
  let encrypted = '';
  let newkey = '';
  
  for (let a=0; a<message.length/key.length; a++) {
    key = shuffle(key, shufflestring)
    charcode = toNumber(key,a%key.length);
    shift = (charcode+shift)%key.length;
    sliceindex = key.length - shift;
    newkey = key.slice(sliceindex) + key.slice(0,sliceindex);
    console.log({charcode, shift, newkey, key});
    for (let b=0; b<key.length; b++) {
      const index = a*key.length+b
      if (index<message.length) {
        encrypted += encryptLetter(message, newkey, index)
      }
    }
  }
  return encrypted;
}
// Only CAPITALS and no punctuation marks
// third argument is the order in which the letters should be moved
// you should randomize the order and send that order with the key
console.log(encrypt(process.argv[2],process.argv[3], 'CLXUIQJPSADOWVHBFYERMGTZKN'))