'use strict';

var LETTERS = 'abcdefghijklmnopqrstuvwxyz';

var REVERSED_LETTERS = 'zyxwvutsrqponmlkjihgfedcba';

function insertSpacing(s, interval) {

var matcher = new RegExp(".{1," + interval + "}", "g");

return s.match(matcher).join(' ');

}

function invert(character) {

/*jshint validthis: true */

if (character.match(/\d/)) {

this.push(character);

} else {

this.push(LETTERS[REVERSED_LETTERS.indexOf(character)]);

}

}

module.exports = {

encode: function (s) {

var encoded = '';

var characters = [];

s.toLowerCase().split('').forEach( invert, characters );

encoded = insertSpacing(characters.join(''), 5);

return encoded;

}

};