vanillaaont/index.js

simple all-or-nothing transform in nothing but vanilla js

"use strict";
{
  const vanillaaont = {
    T,TU
  };

  const alph = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  const dec = "0123456789";
  const twomore = "/+";
  const alphabet = alph + dec + alph.toLowerCase() + twomore;
  const pad = new Array(33).join('0');
  const initial_rotate = 13;
  const rotates = alphabet.
    split('').
    reduce( (m,c,i) => ( m[c] = i+1, m ), {} );
  try { Object.assign( self, { vanillaaont } ); } catch(e) { module.exports = vanillaaont; }

  function t( m ) {
    m = Array.from(m);
    m.reverse();
    const b = Array.from(m);
    let i = -1;
    while( true ) {
      const mc = b[i+1];
      const rotate_amount = i >= 0 ? rotates[mc] : initial_rotate;
      if ( ! rotate_amount ) {
        throw new TypeError(`This string is not in base 64. We only know how to interpret these symbols: ${alphabet}. You provided this: "${mc}"` );
      }
      const remaining = Math.min(m.length - (i+2),alphabet.length);
      if ( i+2 < m.length - 1 ) {
        const rot_sec = rotate_left_by( (rotate_amount) % remaining, b.slice( i+2, i+67 ) );
        b.splice( i+2, 65, ...rot_sec );
      } else {
        break;
      }
      i+=1;
    }
    return b.join('');
  }

  function T( m ) {
    m = Array.from(m);
    let head, tail;
    let tail_start = m.indexOf('=');
    if ( tail_start >= 0 ) {
      head = m.slice(0, tail_start);
      tail = m.slice(tail_start);
    } else {
      head = m;
      tail = [];
    }
    head.unshift(...pad);
    head.push(...pad);
    m = head;
    let r = t(t(t(t(m))));
    r = r + tail.join('');
    return r;
  }

  function tu(m) {
    const b = Array.from(m);
    let j = m.length-1;
    while( j > 0 ) {
      const remaining = Math.min(m.length-j,alphabet.length);
      const mc = b[j-1];
      const rotate_amount = j >= 2 ? rotates[mc] : initial_rotate;
      if ( ! rotate_amount ) {
        throw new TypeError(`This string is not in base 64. We only know how to interpret these symbols: ${alphabet}. You provided this: "${mc}"` );
      }
      const rot_sec = rotate_right_by( (rotate_amount) % remaining, b.slice( j, j+65 ) );
      b.splice( j, 65, ...rot_sec );
      j -= 1;
    }
    b.reverse();
    return b.join('');
  }

  function TU( m ) {
    m = Array.from(m);
    const tail_count = m.filter( mc => mc == "=" ).length;
    if ( tail_count ) {
      m = m.slice(0,m.indexOf('='));
    }
    const b = tu(tu(tu(tu(m)))).split('');
    const result = b.slice(32,-32);
    result.push( ...Array(tail_count+1).join('=') );
    return result.join('');
  }

  function rotate_right_by( amount, array ) {
    let head = array.slice( array.length - amount );
    const tail = array.slice(0,array.length - amount);
    head = head.concat(tail);
    return head;
  }

  function rotate_left_by( amount, array ) {
    let head = array.slice( amount );
    const tail = array.slice(0,amount);
    head = head.concat(tail);
    return head;
  }
}