/* 
 * Copyright (c) <year>, <copyright holder>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the <organization> nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY <copyright holder> ''AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL <copyright holder> BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * TODO:
 * - Support for ISO GUID stanard
*/

function Guid(options) {
  this.options = options || {};
  this.chars = this.options.chars || Guid.constants.alphanumerics;
  this.epoch = this.options.epoch || Guid.constants.epoch1970;
  this.counterSequenceLength = this.options.counterSequenceLength || 1;
  this.randomSequenceLength = this.options.randomSequenceLength || 2;
}

Guid.prototype.generate = function() {
  var now = (new Date()).getTime() - this.epoch;
  var guid = this.baseN(now);

  this.counterSeq = (now==this.lastTimestampUsed ? this.counterSeq+1 : 1);
  guid += this.counterSeq;

  for (var i=0; i<this.randomSequenceLength; i++) {
    guid += this.chars.charAt(Math.floor(Math.random() * this.chars.length));
  }

  this.lastTimestampUsed = now;

  return guid;
}

Guid.prototype.baseN = function(val) {
  if (val==0) return "";
  var rightMost = val % this.chars.length;
  var rightMostChar = this.chars.charAt(rightMost);
  var remaining = Math.floor(val / this.chars.length);
  return this.baseN(remaining) + rightMostChar;
}

Guid.constants = {};
Guid.constants.numbers = "0123456789";
Guid.constants.alphas = "abcdefghijklmnopqrstuvwxyz";
Guid.constants.lowerAlphanumerics = "0123456789abcdefghijklmnopqrstuvwxyz";
Guid.constants.alphanumerics = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
// http://tools.ietf.org/html/rfc1924
Guid.constants.base85 = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!#$%&()*+-;<=>?@^_`{|}~";

Guid.constants.epoch1970 = (new Date(0));
Guid.constants.epoch = function(year) { return (new Date("Jan 1 " + year)).getTime(); }

// function log() { if (console) console.log.apply(console, arguments); }