/**
 使用步骤:
 1、在head区内添加
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

 2、添加引用
 <script src="../../lib/base64.js"></script>

 3、加码
 var a=encode64("黄海");
 console.log(a);

 4、解码
 console.log(decode64(a));

 5、java解码
 final Base64 base64 = new Base64();
 System.out.println(new String(base64.decode("//7Enndt"), "Unicode"));
 */

var keyStr = "ABCDEFGHIJKLMNOP" +
    "QRSTUVWXYZabcdef" +
    "ghijklmnopqrstuv" +
    "wxyz0123456789+/" +
    "=";

function encode64(input) {
    input = unicodetoBytes(input);
    var output = "";
    var chr1, chr2, chr3 = "";
    var enc1, enc2, enc3, enc4 = "";
    var i = 0;

    do {
        chr1 = input[i++];
        chr2 = input[i++];
        chr3 = input[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);
        chr1 = chr2 = chr3 = "";
        enc1 = enc2 = enc3 = enc4 = "";
    } while (i < input.length);

    return output;
}

function decode64(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 =
    var base64test = /[^A-Za-z0-9/+///=]/g;
    if (base64test.exec(input)) {
        alert("There were invalid base64 characters in the input text./n" +
            "Valid base64 characters are A-Z, a-z, 0-9, '+', '/', and '='/n" +
            "Expect errors in decoding.");
    }
    input = input.replace(/[^A-Za-z0-9/+///=]/g, "");
    output=new Array();
    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.push(chr1);
        if (enc3 != 64) {
            output.push(chr2);
        }
        if (enc4 != 64) {
            output.push(chr3);
        }

        chr1 = chr2 = chr3 = "";
        enc1 = enc2 = enc3 = enc4 = "";

    } while (i < input.length);
    return bytesToUnicode(output);
}

function unicodetoBytes(s)
{
    var result=new Array();
    if(s==null || s=="") return result;
    result.push(255); // add "FE" to head
    result.push(254);
    for(var i=0;i<s.length;i++)
    {
        var c=s.charCodeAt(i).toString(16);
        if(c.length==1) i="000"+c;
        else if(c.length==2) c="00"+c;
        else if(c.length==3) c="0"+c;
        var var1=parseInt( c.substring(2),16);
        var var2=parseInt( c.substring(0,2),16);
        result.push( var1);
        result.push(var2) ;
    }
    return result;
}

function bytesToUnicode(bs)
{
    var result="";
    var offset=0;
    if(bs.length>=2 && bs[0]==255 && bs[1]==254) offset=2;  // delete "FE"
    for(var i=offset;i<bs.length;i+=2)
    {
        var code=bs[i]+(bs[i+1]<<8);
        result+=String.fromCharCode(code);
    }
    return result;
}