/* 
  * Copyright (c) 2010 Nick Galbreath 
  * http://code.google.com/p/stringencoders/source/browse/#svn/trunk/javascript 
  * 
  * Permission is hereby granted, free of charge, to any person 
  * obtaining a copy of this software and associated documentation 
  * files (the "Software"), to deal in the Software without 
  * restriction, including without limitation the rights to use, 
  * copy, modify, merge, publish, distribute, sublicense, and/or sell 
  * copies of the Software, and to permit persons to whom the 
  * Software is furnished to do so, subject to the following 
  * conditions: 
  * 
  * The above copyright notice and this permission notice shall be 
  * included in all copies or substantial portions of the Software. 
  * 
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES 
  * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT 
  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
  * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR 
  * OTHER DEALINGS IN THE SOFTWARE. 
  */ 
  
 /* base64 encode/decode compatible with window.btoa/atob 
  * 
  * window.atob/btoa is a Firefox extension to convert binary data (the "b") 
  * to base64 (ascii, the "a"). 
  * 
  * It is also found in Safari and Chrome.  It is not available in IE. 
  * 
  * if (!window.btoa) window.btoa = base64.encode 
  * if (!window.atob) window.atob = base64.decode 
  * 
  * The original spec's for atob/btoa are a bit lacking 
  * https://developer.mozilla.org/en/DOM/window.atob 
  * https://developer.mozilla.org/en/DOM/window.btoa 
  * 
  * window.btoa and base64.encode takes a string where charCodeAt is [0,255] 
  * If any character is not [0,255], then an DOMException(5) is thrown. 
  * 
  * window.atob and base64.decode take a base64-encoded string 
  * If the input length is not a multiple of 4, or contains invalid characters 
  *   then an DOMException(5) is thrown. 
  */ 
 var base64 = {}; 
 base64.PADCHAR = '='; 
 base64.ALPHA = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'; 
  
 base64.makeDOMException = function() { 
     // sadly in FF,Safari,Chrome you can't make a DOMException 
     var e, tmp; 
  
     try { 
         return new DOMException(DOMException.INVALID_CHARACTER_ERR); 
     } catch (tmp) { 
         // not available, just passback a duck-typed equiv 
         // https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Error 
         // https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Error/prototype 
         var ex = new Error("DOM Exception 5"); 
  
         // ex.number and ex.description is IE-specific. 
         ex.code = ex.number = 5; 
         ex.name = ex.description = "INVALID_CHARACTER_ERR"; 
  
         // Safari/Chrome output format 
         ex.toString = function() { return 'Error: ' + ex.name + ': ' + ex.message; }; 
         return ex; 
     } 
 } 
  
 base64.getbyte64 = function(s,i) { 
     // This is oddly fast, except on Chrome/V8. 
     //  Minimal or no improvement in performance by using a 
     //   object with properties mapping chars to value (eg. 'A': 0) 
     var idx = base64.ALPHA.indexOf(s.charAt(i)); 
     if (idx === -1) { 
         throw base64.makeDOMException(); 
     } 
     return idx; 
 } 
  
 base64.decode = function(s) { 
     // convert to string 
     s = '' + s; 
     var getbyte64 = base64.getbyte64; 
     var pads, i, b10; 
     var imax = s.length 
     if (imax === 0) { 
         return s; 
     } 
  
     if (imax % 4 !== 0) { 
         throw base64.makeDOMException(); 
     } 
  
     pads = 0 
     if (s.charAt(imax - 1) === base64.PADCHAR) { 
         pads = 1; 
         if (s.charAt(imax - 2) === base64.PADCHAR) { 
             pads = 2; 
         } 
         // either way, we want to ignore this last block 
         imax -= 4; 
     } 
  
     var x = []; 
     for (i = 0; i < imax; i += 4) { 
         b10 = (getbyte64(s,i) << 18) | (getbyte64(s,i+1) << 12) | 
             (getbyte64(s,i+2) << 6) | getbyte64(s,i+3); 
         x.push(String.fromCharCode(b10 >> 16, (b10 >> 8) & 0xff, b10 & 0xff)); 
     } 
  
     switch (pads) { 
     case 1: 
         b10 = (getbyte64(s,i) << 18) | (getbyte64(s,i+1) << 12) | (getbyte64(s,i+2) << 6); 
         x.push(String.fromCharCode(b10 >> 16, (b10 >> 8) & 0xff)); 
         break; 
     case 2: 
         b10 = (getbyte64(s,i) << 18) | (getbyte64(s,i+1) << 12); 
         x.push(String.fromCharCode(b10 >> 16)); 
         break; 
     } 
     return x.join(''); 
 } 
  
 base64.getbyte = function(s,i) { 
     var x = s.charCodeAt(i); 
     if (x > 255) { 
         throw base64.makeDOMException(); 
     } 
     return x; 
 } 
  
 base64.encode = function(s) { 
     if (arguments.length !== 1) { 
         throw new SyntaxError("Not enough arguments"); 
     } 
     var padchar = base64.PADCHAR; 
     var alpha   = base64.ALPHA; 
     var getbyte = base64.getbyte; 
  
     var i, b10; 
     var x = []; 
  
     // convert to string 
     s = '' + s; 
  
     var imax = s.length - s.length % 3; 
  
     if (s.length === 0) { 
         return s; 
     } 
     for (i = 0; i < imax; i += 3) { 
         b10 = (getbyte(s,i) << 16) | (getbyte(s,i+1) << 8) | getbyte(s,i+2); 
         x.push(alpha.charAt(b10 >> 18)); 
         x.push(alpha.charAt((b10 >> 12) & 0x3F)); 
         x.push(alpha.charAt((b10 >> 6) & 0x3f)); 
         x.push(alpha.charAt(b10 & 0x3f)); 
     } 
     switch (s.length - imax) { 
     case 1: 
         b10 = getbyte(s,i) << 16; 
         x.push(alpha.charAt(b10 >> 18) + alpha.charAt((b10 >> 12) & 0x3F) + 
                padchar + padchar); 
         break; 
     case 2: 
         b10 = (getbyte(s,i) << 16) | (getbyte(s,i+1) << 8); 
         x.push(alpha.charAt(b10 >> 18) + alpha.charAt((b10 >> 12) & 0x3F) + 
                alpha.charAt((b10 >> 6) & 0x3f) + padchar); 
         break; 
     } 
     return x.join(''); 
 }