//This is a list of XMLHttpRequest-creation factory functions to try
var HTTP = function(){}
HTTP._factories = [
    function() { return new XMLHttpRequest(); },
    function() { return new ActiveXObject("Msxml2.XMLHTTP"); },
    function() { return new ActiveXObject("Microsoft.XMLHTTP"); }
];

// When we find a factory that works, store it here.
HTTP._factory = null;

// Create and return a new XMLHttpRequest object.
//
// The first time we're called, try the list of factory functions until
// we find one that returns a non-null value and does not throw an
// exception. Once we find a working factory, remember it for later use.
//
HTTP.newRequest = function() {
    if (HTTP._factory != null) return HTTP._factory();

    for(var i = 0; i < HTTP._factories.length; i++) {
        try {
            var factory = HTTP._factories[i];
            var request = factory();
            if (request != null) {
                HTTP._factory = factory;
                return request;
            }
        }
        catch(e) {
            continue;
        }
    }
    // If we get here, none of the factory candidates succeeded,
    // so throw an exception now and for all future calls.
    HTTP._factory 
 = function() {
        throw new Error("XMLHttpRequest not supported");
    }
    HTTP._factory(); // Throw an error
}

/**
 * Send an HTTP POST request to the specified URL, using the names and values
 * of the properties of the values object as the body of the request.
 * Parse the server's response according to its content type and pass
 * the resulting value to the callback function. If an HTTP error occurs,
 * call the specified errorHandler function, or pass null to the callback
 * if no error handler is specified.
 **/
HTTP.post = function(url, values, callback, errorHandler) {
    var request = HTTP.newRequest();
    request.onreadystatechange = function() {
        if (request.readyState == 4) {
            if (request.status == 200) {
                callback(HTTP._getResponse(request));
            }
            else {
                if (errorHandler) errorHandler(request.status,
                                               request.statusText);
                else callback(null);
            }
        }
    }

    request.open("POST", url);
    // This header tells the server how to interpret the body of the request.
    request.setRequestHeader("Content-Type",
                             "application/x-www-form-urlencoded");
    
    //request.setRequestHeader("Accept-Charset", "gbk");

    // Encode the properties of the values object and send them as
    // the body of the request.
    request.send(HTTP.encodeFormData(values));
};
/**
 * Send an HTTP POST request to the specified URL, using the names and values
 * of the properties of the values object as the body of the request.
 * Parse the server's response according to its content type and pass
 * the resulting value to the callback function. If an HTTP error occurs,
 * call the specified errorHandler function, or pass null to the callback
 * if no error handler is specified.
 **/
HTTP.get = function(url, values, callback, errorHandler) {
    var request = HTTP.newRequest();
    request.onreadystatechange = function() {
        if (request.readyState == 4) {
            if (request.status == 200) {
            	if(null != callback){
            		callback(HTTP._getResponse(request));
            	}
            }
            else {
                if (errorHandler) errorHandler(request.status,
                                               request.statusText);
                else callback(null);
            }
        }
    }
    request.open("GET", url+"?"+HTTP.encodeFormData(values));
    // This header tells the server how to interpret the body of the request.
    request.setRequestHeader("Content-Type",
                             "text/plain;charset=gbk");
    // Encode the properties of the values object and send them as
    // the body of the request.
    request.send(null);
};

/**
 * Encode the property name/value pairs of an object as if they were from
 * an HTML form, using application/x-www-form-urlencoded format
 */
HTTP.encodeFormData = function(data) {
	if(data !=null && data !="undefined" && data !=""){
	    var pairs = [];
	    var regexp = /%20/g; // A regular expression to match an encoded space
	
	    for(var name in data) {
	        var value = data[name].toString();
	        // Create a name/value pair, but encode name and value first
	        // The global function encodeURIComponent does almost what we want,
	        // but it encodes spaces as %20 instead of as "+". We have to
	        // fix that with String.replace()
	       // var pair = encodeURIComponent(name).replace(regexp,"+") + '=' +
	       //    encodeURIComponent(value).replace(regexp,"+");
	        var pair = name + '=' + escape(value);
	        //var pair = name + '=' +
	        //value;
	        pairs.push(pair);
	    }
	
	    // Concatenate all the name/value pairs, separating them with &
	    return pairs.join('&');
	}else{
		return null;
	}
};

HTTP._getResponse = function(request) {
    // Check the content type returned by the server
    switch(request.getResponseHeader("Content-Type")) {
    case "text/xml":
        // If it is an XML document, use the parsed Document object.
        return request.responseXML;

    case "text/json":
    case "text/javascript":
    case "application/javascript":
    case "application/x-javascript":
        // If the response is JavaScript code, or a JSON-encoded value,
        // call eval() on the text to "parse" it to a JavaScript value.
        // Note: only do this if the JavaScript code is from a trusted server!
        return eval(request.responseText);

    default:
        // Otherwise, treat the response as plain text and return as a string.
        return request.responseText;
    }
};