HORIZON PROJECT

'use strict';

var alphabet = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_'.split('')

  , length = 64

  , map = {}

  , seed = 0

  , i = 0

  , prev;

/**

 * Return a string representing the specified number.

 *

 * @param {Number} num The number to convert.

 * @returns {String} The string representation of the number.

 * @api public

 */

function encode(num) {

  var encoded = '';

  do {

    encoded = alphabet[num % length] + encoded;

    num = Math.floor(num / length);

  } while (num > 0);

  return encoded;

}

/**

 * Return the integer value specified by the given string.

 *

 * @param {String} str The string to convert.

 * @returns {Number} The integer value represented by the string.

 * @api public

 */

function decode(str) {

  var decoded = 0;

  for (i = 0; i < str.length; i++) {

    decoded = decoded * length + map[str.charAt(i)];

  }

  return decoded;

}

/**

 * Yeast: A tiny growing id generator.

 *

 * @returns {String} A unique id.

 * @api public

 */

function yeast() {

  var now = encode(+new Date());

  if (now !== prev) return seed = 0, prev = now;

  return now +'.'+ encode(seed++);

}

//

// Map each character to its index.

//

for (; i < length; i++) map[alphabet[i]] = i;

//

// Expose the `yeast`, `encode` and `decode` functions.

//

yeast.encode = encode;

yeast.decode = decode;

module.exports = yeast;