romanos.js

//
// Escolhe qual conversão utilizar dependendo do input
//
function converter(input) {
  if (typeof input === 'number') {
    return toRoman(input);
  }
  else {
    return toIndu(input);
  }
}


// 
// Converte algarismos romanos para indu-arábicos
// 
function toIndu(roman) {

  var roman      = roman.split('');
  var matrix     = {'I': 1, 'V': 5, 'X': 10, 'L': 50,  'C': 100, 'D': 500,  'M': 1000 };
  var order      = ['I', 'V', 'X', 'L', 'C', 'D', 'M'];

  // 
  // Validações
  // 
  if (roman.some(nextFiveInvalid) || ! roman.every(nextBiggerValid) || roman.some(fourEquals)) {
    return false;
  }

  //
  // Engine da parada
  // 
  function convert(indu, letter, index, roman) {
    if (nextBigger(letter, index, roman)) {
        indu -= matrix[letter];
    }
    else {
      indu += matrix[letter];
    }
    return indu;
  }


  //
  // Aplica engine para cada um dos algarismos
  //
  return roman.reduce(convert, 0);


  //
  // Fuções utilitárias
  // 
  function hasNext(letter, index, roman) {
    return typeof roman[index + 1] === 'string';
  }

  
  function nextEqual(letter, index, roman) {
    return hasNext(letter, index, roman) 
      && roman[index] === roman[index + 1];
  }

  
  function nextBigger(letter, index, roman) {
    return hasNext(letter, index, roman) 
      && matrix[roman[index + 1]] > matrix[roman[index]];
  }

  
  function biggerValid(letter, index, roman) {
    return (order.indexOf(roman[index + 1]) - order.indexOf(roman[index])) <= 2 
      &&  (matrix[roman[index + 1]] / matrix[letter]) != 2;
  }

  
  function nextBiggerValid(letter, index, roman) {
    return ! nextBigger(letter, index, roman) 
      || biggerValid(letter, index, roman);
  }


  function nextFiveInvalid(letter, index, roman) {
    return nextEqual(letter, index, roman) 
      && beginsWithFive(letter[index]);
  }


  function beginsWithFive(value) {
    return new String(matrix[value])[0] === '5';
  }


  function fourEquals(letter, index, roman) {
    return nextEqual(letter, index, roman)  
      && nextEqual(letter, index + 1, roman) 
      && nextEqual(letter, index + 2, roman) 
  }

}



//
// Converte algarismos indu-arábicos para romanos
// 
function toRoman(indu) {

  var r1000 = convert(indu,       1000, 'M'); //console.log(r1000)
  var r100  = convert(r1000.indu, 100,  'C', 'D', 'M'); //console.log(r100)
  var r10   = convert(r100.indu,  10,   'X', 'L', 'C'); //console.log(r10)
  var r1    = convert(r10.indu,   1,    'I', 'V', 'X'); //console.log(r1)

  return r1000.roman + r100.roman + r10.roman + r1.roman;


  function repeat(times, char) {
    var snippet = '';
    for (var i = 0; i < times; i++) {
      snippet += char;
    }
    return snippet;
  }
  
  
  function convert(indu, base, low, middle, high) {
    var roman = ''
    var times;

    if (indu >= (1 * base) && indu < (4 * base)) {
      times = Math.floor(indu / base);
      roman = repeat(times, low);
      indu -= (times * base);
    }
    else if (indu >= (4 * base) && indu < (5 * base)) {
      times = Math.floor(indu / base);
      roman = low + middle;
      indu -= (times * base);
    }
    else if (indu === (5 * base)) {
      roman = middle;
    }
    else if (indu > (5 * base) && indu < (9 * base)) {
      times = Math.floor(indu / base) - 5;
      roman = middle + repeat(times, low);
      indu -= (times * base + (5 * base));
    }
    else if (indu >= (9 * base) && indu < (10 * base)) {
      roman = low + high;
      indu -= (9 * base);
    }
    else if (indu === (10 * base)) {
      roman = high;
    }
    
    return {
      roman: roman, 
      indu: indu
    };
  }
}