var Base64 = {
    _keyStr: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=',
    encode(str) {
        // 加密
        var output = '';
        var chr1;
        var chr2;
        var chr3;
        var enc1;
        var enc2;
        var enc3;
        var enc4;
        var i = 0;
        str = this._utf16to8(str);
        while (i < str.length) {
            chr1 = str.charCodeAt(i++);
            chr2 = str.charCodeAt(i++);
            chr3 = str.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 + this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) + this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);
        }
        return output;
    },
    decode(input) {
        // 解密
        var output = '';
        var chr1;
        var chr2;
        var chr3;
        var enc1;
        var enc2;
        var enc3;
        var enc4;
        var i = 0;
        input = input.replace(/[^A-Za-z0-9\+\/\=]/g, '');
        while (i < input.length) {
            enc1 = this._keyStr.indexOf(input.charAt(i++));
            enc2 = this._keyStr.indexOf(input.charAt(i++));
            enc3 = this._keyStr.indexOf(input.charAt(i++));
            enc4 = this._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) {
                output = output + String.fromCharCode(chr2);
            }
            if (enc4 != 64) {
                output = output + String.fromCharCode(chr3);
            }
        }
        return this._utf8to16(output);
    },
    _utf16to8: function (str) {
        var out;
        var i;
        var len;
        var c;
        out = '';
        len = str.length;
        for (i = 0; i < len; i++) {
            c = str.charCodeAt(i);
            if (c >= 1 && c <= 127) {
                out += str.charAt(i);
            } else if (c > 2047) {
                out += String.fromCharCode(224 | ((c >> 12) & 15));
                out += String.fromCharCode(128 | ((c >> 6) & 63));
                out += String.fromCharCode(128 | ((c >> 0) & 63));
            } else {
                out += String.fromCharCode(192 | ((c >> 6) & 31));
                out += String.fromCharCode(128 | ((c >> 0) & 63));
            }
        }
        return out;
    },
    _utf8to16(str) {
        var out;
        var i;
        var len;
        var c;
        var char2;
        var char3;
        out = '';
        len = str.length;
        i = 0;
        while (i < len) {
            c = str.charCodeAt(i++);
            switch (c >> 4) {
                case 0:
                case 1:
                case 2:
                case 3:
                case 4:
                case 5:
                case 6:
                    case7: out += str.charAt(i - 1);
                    break;
                case 12:
                case 13:
                    char2 = str.charCodeAt(i++);
                    out += String.fromCharCode(((c & 31) << 6) | (char2 & 63));
                    break;
                case 14:
                    char2 = str.charCodeAt(i++);
                    char3 = str.charCodeAt(i++);
                    out += String.fromCharCode(((c & 15) << 12) | ((char2 & 63) << 6) | ((char3 & 63) << 0));
                    break;
            }
        }
        return out;
    }
};

/* 暴露函数 */
module.exports = Base64;
