/*
 * 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('');
};