/*==================================================
 *  XmlHttp Utility Functions
 *==================================================
 */

Timeline.XmlHttp = new Object();

/**
 *  Callback for XMLHttp onRequestStateChange.
 */
Timeline.XmlHttp._onReadyStateChange = function(xmlhttp, fError, fDone) {
    switch (xmlhttp.readyState) {
    // 1: Request not yet made
    // 2: Contact established with server but nothing downloaded yet
    // 3: Called multiple while downloading in progress
    
    // Download complete
    case 4:
        try {
            if (xmlhttp.status == 0     // file:// urls, works on Firefox
             || xmlhttp.status == 200   // http:// urls
            ) {
                if (fDone) {
                    fDone(xmlhttp);
                }
            } else {
                if (fError) {
                    fError(
                        xmlhttp.statusText,
                        xmlhttp.status,
                        xmlhttp
                    );
                }
            }
        } catch (e) {
            Timeline.Debug.exception(e);
        }
        break;
    }
};

/**
 *  Creates an XMLHttpRequest object. On the first run, this
 *  function creates a platform-specific function for
 *  instantiating an XMLHttpRequest object and then replaces
 *  itself with that function.
 */
Timeline.XmlHttp._createRequest = function() {
    if (Timeline.Platform.browser.isIE) {
        var programIDs = [
        "Msxml2.XMLHTTP",
        "Microsoft.XMLHTTP",
        "Msxml2.XMLHTTP.4.0"
        ];
        for (var i = 0; i < programIDs.length; i++) {
            try {
                var programID = programIDs[i];
                var f = function() {
                    return new ActiveXObject(programID);
                };
                var o = f();
                
                // We are replacing the Timeline._createXmlHttpRequest
                // function with this inner function as we've
                // found out that it works. This is so that we
                // don't have to do all the testing over again
                // on subsequent calls.
                Timeline.XmlHttp._createRequest = f;
                
                return o;
            } catch (e) {
                // silent
            }
        }
        throw new Error("Failed to create an XMLHttpRequest object");
    } else {
        try {
            var f = function() {
                return new XMLHttpRequest();
            };
            var o = f();
            
            // We are replacing the Timeline._createXmlHttpRequest
            // function with this inner function as we've
            // found out that it works. This is so that we
            // don't have to do all the testing over again
            // on subsequent calls.
            Timeline.XmlHttp._createRequest = f;
            
            return o;
        } catch (e) {
            throw new Error("Failed to create an XMLHttpRequest object");
        }
    }
};

/**
 *  Performs an asynchronous HTTP GET.
 *  fError is of the form function(statusText, statusCode, xmlhttp).
 *  fDone is of the form function(xmlhttp).
 */
Timeline.XmlHttp.get = function(url, fError, fDone) {
    var xmlhttp = Timeline.XmlHttp._createRequest();
    
    xmlhttp.open("GET", url, true);
    xmlhttp.onreadystatechange = function() {
        Timeline.XmlHttp._onReadyStateChange(xmlhttp, fError, fDone);
    };
    xmlhttp.send(null);
};

/**
 *  Performs an asynchronous HTTP POST.
 *  fError is of the form function(statusText, statusCode, xmlhttp).
 *  fDone is of the form function(xmlhttp).
 */
Timeline.XmlHttp.post = function(url, body, fError, fDone) {
    var xmlhttp = Timeline.XmlHttp._createRequest();
    
    xmlhttp.open("POST", url, true);
    xmlhttp.onreadystatechange = function() {
        Timeline.XmlHttp._onReadyStateChange(xmlhttp, fError, fDone);
    };
    xmlhttp.send(body);
};

Timeline.XmlHttp._forceXML = function(xmlhttp) {
    try {
        xmlhttp.overrideMimeType("text/xml");
    } catch (e) {
        xmlhttp.setrequestheader("Content-Type", "text/xml");
    }
};