to_comparative.js

'use strict';
const convertables = require('../../data/convertables.js');

const to_comparative = function(str) {
  const irregulars = {
    'grey': 'greyer',
    'gray': 'grayer',
    'green': 'greener',
    'yellow': 'yellower',
    'red': 'redder',
    'good': 'better',
    'well': 'better',
    'bad': 'worse',
    'sad': 'sadder'
  };

  const dont = {
    'overweight': 1,
    'main': 1,
    'nearby': 1,
    'asleep': 1,
    'weekly': 1,
    'secret': 1,
    'certain': 1
  };

  const transforms = [{
    reg: /y$/i,
    repl: 'ier'
  }, {
    reg: /([aeiou])t$/i,
    repl: '$1tter'
  }, {
    reg: /([aeou])de$/i,
    repl: '$1der'
  }, {
    reg: /nge$/i,
    repl: 'nger'
  }];

  const matches = [
    /ght$/,
    /nge$/,
    /ough$/,
    /ain$/,
    /uel$/,
    /[au]ll$/,
    /ow$/,
    /old$/,
    /oud$/,
    /e[ae]p$/
  ];

  const not_matches = [
    /ary$/,
    /ous$/
  ];

  if (dont.hasOwnProperty(str)) {
    return null;
  }

  for (let i = 0; i < transforms.length; i++) {
    if (str.match(transforms[i].reg)) {
      return str.replace(transforms[i].reg, transforms[i].repl);
    }
  }

  if (convertables.hasOwnProperty(str)) {
    if (str.match(/e$/)) {
      return str + 'r';
    }
    return str + 'er';
  }

  if (irregulars.hasOwnProperty(str)) {
    return irregulars[str];
  }

  for (let i = 0; i < not_matches.length; i++) {
    if (str.match(not_matches[i])) {
      return 'more ' + str;
    }
  }

  for (let i = 0; i < matches.length; i++) {
    if (str.match(matches[i])) {
      return str + 'er';
    }
  }
  return 'more ' + str;
};