bacon cipher

var bacon = (function () {

    var bacon = {},
        defaultBase = 2;

    function getEncodedWidth(alphabet, base) {
        var width = 1 + Math.floor(Math.log(alphabet.length) / Math.log(base));
        return width;
    }

    function padLeft(str, char, length) {
        var padLength = Math.max(length - str.length);
        var pad = Math.pow(10, padLength).toString().substr(-padLength).replace('0', char);

        return pad + str;
    }

    function getMap(alphabet, base) {
        var baseMap = bacon[base];

        if (!baseMap) {
            bacon[base] = baseMap = {};
        }

        var alphaMap = baseMap[alphabet];
        if (!alphaMap) {
            var width = getEncodedWidth(alphabet, base);
            baseMap[alphabet] = alphaMap = [].reduce.call(alphabet, function (m, c, i) {
                var value = i.toString(base);
                value = padLeft(value, '0', width);
                m.encodings[c] = value;
                m.decodings[value] = c;
                return m;
            }, { encodings: {}, decodings: {} });
        }

        return alphaMap;
    }

    function encode(value, alphabet, base) {
        base = Math.abs(base) || defaultBase;

        var map = getMap(alphabet, base);
        var encodings = [].map.call(value, function (c) {
            return map.encodings[c];
        });

        return encodings.join('');
    }

    function decode(value, alphabet, base) {
        base = Math.abs(base) || defaultBase;

        var width = getEncodedWidth(alphabet, base);
        var map = getMap(alphabet, base);
        var characters = value.match(new RegExp('.{' + width + '}', 'g'));
        var decodings = characters.map(function (c) {
            return map.decodings[c];
        });

        return decodings.join('');
    }

    return {
        encode: encode,
        decode: decode
    };
})();