WebTools = {};

/**
 * @param       String                                                          method
 * @param       String                                                          URL
 * @param       String                                                          postData
 * @param       Function(responseData)                                          onSuccess
 * @param       Function(Integer HTTPStatusCode, String responseData)           onSuccess
 * @return      void
 */
WebTools.requestURL = function(method, URL, postData, onSuccess, onFail)
{
    var XHR = new XMLHttpRequest();
    XHR.open(method, URL, true);
    XHR.setRequestHeader("Content-type", "application/x-www-form-urlencoded; charset=UTF-8");
    XHR.setRequestHeader("Pragma", "no-cache");
    XHR.setRequestHeader("Cache-Control", "no-cache");
    XHR.onreadystatechange = function(){
        if(XHR.status == 0)
            return onFail(XHR.status);
        if(XHR.readyState == 4)
            if(XHR.status == 200)
                onSuccess(XHR.responseText);
            else
                onFail(XHR.status, XHR.responseText);
    };
    XHR.send(postData);
};

WebTools.parseDocument = function(HTMLString)
{
    var doc = new DOMParser;
    doc.parseFromString(req.response, 'text/html');
    return doc;
};



var ZachSite = function(elementContent){
    var THIS = this;
    THIS.elementContent = elementContent;
    window.addEventListener("popstate", function(ev){
        if(ev.state.zachSiteURLRequest){
            THIS.loadSitePage(location.href);
        }
    });
};

ZachSite.prototype.registerLink = function(elmLink){
    if(!elmAnchor instanceof HTMLAnchorElement)
        throw new TypeError("Only HTMLAnchorElements");

    elmLink.addEventListener("click", function(ev){
        if(this.host == location.host && (this.pathname != location.pathname || this.search != location.search)){
            ev.preventDefault();
            history.pushState({zachSiteURLRequest: true}, this.textContent, this.href);
        }
    });
};

ZachSite.prototype.loadSitePage = function(URL)
{
    var THIS = this;

    var onSuccess = function(responseData)
    {
        var newDocument = WebTools.parseDocument(responseData);
        var newContent = newDocument.getElementById("content");
        // removes old #content contents
        while(THIS.elementContent.children)
            THIS.elementContent.removeChild(THIS.elementContent.children[0]);
        // appends new #content contents
        while(newContent.children)
            THIS.elementContent.appendChild(newContent.children[0]);
        // updates the title
        document.title = newDocument.title;
    };

    var onFail = function(httpstatus, data){
        alert("Page request returned an error: " + httpstatus + "\n " + data);
    };

    WebTools.requestURL = function("GET", URL, null, onSuccess, onFail);
    document.title = "@@@@@ LOADING!!! @@@@@"; // you can show a loading gif here (and hide it inside onSuccess|onFail())
};


var site = new ZachSite(document.getElementById("content"));
var siteLinks = document.getElementsByTagName("a");
for(var x=0; x<siteLinks.length; x++)
    site.registerLink(siteLinks[x]);