var ALPHA_INDEX = {
    '&lt': '<',
    '&gt': '>',
    '&quot': '"',
    '&apos': '\'',
    '&amp': '&',
    '&lt;': '<',
    '&gt;': '>',
    '&quot;': '"',
    '&apos;': '\'',
    '&amp;': '&'
};

var CHAR_INDEX = {
    60: 'lt',
    62: 'gt',
    34: 'quot',
    39: 'apos',
    38: 'amp'
};

var CHAR_S_INDEX = {
    '<': '&lt;',
    '>': '&gt;',
    '"': '&quot;',
    '\'': '&apos;',
    '&': '&amp;'
};

/**
 * @constructor
 */
function XmlEntities() {}

/**
 * @param {String} str
 * @returns {String}
 */
XmlEntities.prototype.encode = function(str) {
    if (str.length === 0) {
        return '';
    }
    return str.replace(/<|>|"|'|&/g, function(s) {
        return CHAR_S_INDEX[s];
    });
};

/**
 * @param {String} str
 * @returns {String}
 */
 XmlEntities.encode = function(str) {
    return new XmlEntities().encode(str);
 };

/**
 * @param {String} str
 * @returns {String}
 */
XmlEntities.prototype.decode = function(str) {
    if (str.length === 0) {
        return '';
    }
    return str.replace(/&#?[0-9a-zA-Z]+;?/g, function(s) {
        if (s.charAt(1) === '#') {
            var code = s.charAt(2).toLowerCase() === 'x' ?
                parseInt(s.substr(3), 16) :
                parseInt(s.substr(2));

            if (isNaN(code) || code < -32768 || code > 65535) {
                return '';
            }
            return String.fromCharCode(code);
        }
        return ALPHA_INDEX[s] || s;
    });
};

/**
 * @param {String} str
 * @returns {String}
 */
 XmlEntities.decode = function(str) {
    return new XmlEntities().decode(str);
 };

/**
 * @param {String} str
 * @returns {String}
 */
XmlEntities.prototype.encodeNonUTF = function(str) {
    var strLength = str.length;
    if (strLength === 0) {
        return '';
    }
    var result = '';
    var i = 0;
    while (i < strLength) {
        var c = str.charCodeAt(i);
        var alpha = CHAR_INDEX[c];
        if (alpha) {
            result += "&" + alpha + ";";
            i++;
            continue;
        }
        if (c < 32 || c > 126) {
            result += '&#' + c + ';';
        } else {
            result += str.charAt(i);
        }
        i++;
    }
    return result;
};

/**
 * @param {String} str
 * @returns {String}
 */
 XmlEntities.encodeNonUTF = function(str) {
    return new XmlEntities().encodeNonUTF(str);
 };

/**
 * @param {String} str
 * @returns {String}
 */
XmlEntities.prototype.encodeNonASCII = function(str) {
    var strLenght = str.length;
    if (strLenght === 0) {
        return '';
    }
    var result = '';
    var i = 0;
    while (i < strLenght) {
        var c = str.charCodeAt(i);
        if (c <= 255) {
            result += str[i++];
            continue;
        }
        result += '&#' + c + ';';
        i++;
    }
    return result;
};

/**
 * @param {String} str
 * @returns {String}
 */
 XmlEntities.encodeNonASCII = function(str) {
    return new XmlEntities().encodeNonASCII(str);
 };

module.exports = XmlEntities;