simple markov-powered text corruptor

corrupt_test.js

// @ts-check

/**
 * Markov transition table on characters.
 * Empty means "transparent", i.e let the underlying string through
 *
 * @typedef {Object<string, number>} Weights
 * @typedef {Object<string, Weights>} Transitions
 */

/**
 * Steps through a transition table.
 *
 * @param {Transitions} table
 * @param {string} c
 */
function next(table, c) {
  const poss = table[c];
  if (!poss) return '';
  let choice='', best=NaN;
  for (const [char, weight] of Object.entries(poss)) {
    const score = Math.pow(Math.random(), 1/weight);
    if (isNaN(best) || score > best)
      choice=char, best=score;
  }
  return choice;
}

const succ = {
  '':  {'!': 1, '@': 1, '?': 1, '.': 1},
  '!': {'@': 5, '': 3},
  '@': {'?': 5, '': 3},
  '?': {'!': 5, '': 3},
  '.': {'.': 5, '': 3},
};

/** @param {string} s */
function corrupt(s) {
  let state = next(succ, '');
  let r = '';
  for (let i=0; i<s.length; i++) {
    state = next(succ, state);
    r += state ? state : s[i];
  }
  return r;
}

console.log(corrupt('hello'));
console.log(corrupt('world'));
console.log(corrupt('secret'));