var keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-,";

function encode64(input) {
    if (input == null) {
        return null;
    }

    if (input.length > 4 && input.charAt(0) == '_'  && input.charAt(1) == '_'
            && input.charAt(input.length - 2) == '_' && input.charAt(input.length - 1) == '_') {
        //this is encoded... don't reencode
        return input;
    }

    var output = "";
    var chr1, chr2, chr3;
    var enc1, enc2, enc3, enc4;
    var i = 0;

    do {
        chr1 = input.charCodeAt(i++);
        chr2 = input.charCodeAt(i++);
        chr3 = input.charCodeAt(i++);

        enc1 = chr1 >> 2;
        enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
        enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
        enc4 = chr3 & 63;

        if (isNaN(chr2)) {
            enc3 = enc4 = 64;
        } else if (isNaN(chr3)) {
            enc4 = 64;
        }

        output = output + keyStr.charAt(enc1) + keyStr.charAt(enc2) +
            keyStr.charAt(enc3) + keyStr.charAt(enc4);
    } while (i < input.length);

    return '__' + output + '__';
}

function decode64(input) {
    if (input == null) {
        return null;
    }

    if (input.length > 4 && input.charAt(0) == '_'  && input.charAt(1) == '_'
            && input.charAt(input.length - 2) == '_' && input.charAt(input.length - 1) == '_') {
        //this is encoded... we can decode after clipping underscores
        input = input.substring(2, input.length - 2);
    } else {
        //this string is not encoded... let's return
        return input;
    }

    var output = "";
    var chr1, chr2, chr3;
    var enc1, enc2, enc3, enc4;
    var i = 0;

    // remove all characters that are not A-Z, a-z, 0-9, +, /, or =
    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");

    do {
        enc1 = keyStr.indexOf(input.charAt(i++));
        enc2 = keyStr.indexOf(input.charAt(i++));
        enc3 = keyStr.indexOf(input.charAt(i++));
        enc4 = keyStr.indexOf(input.charAt(i++));

        chr1 = (enc1 << 2) | (enc2 >> 4);
        chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
        chr3 = ((enc3 & 3) << 6) | enc4;

        output = output + String.fromCharCode(chr1);

        if ((enc3 != 64) && (chr2 !=0)) {
            output = output + String.fromCharCode(chr2);
        }
        if ((enc4 != 64) && (chr3 !=0)) {
            output = output + String.fromCharCode(chr3);
        }
    } while (i < input.length);

    return output;
}