// global flag
var isIE = false;

// global request and XML document objects
var req;
var pulldownToPopulate;

// retrieve XML document (reusable generic function);
// parameter is URL string (relative or complete) to
// an .xml file whose Content-Type is a valid XML
// type, such as text/xml; XML source must be from
// same domain as HTML file
function loadXMLDoc(url, pulldown) {
	pulldownToPopulate = pulldown;
	
    // branch for native XMLHttpRequest object
    if (window.XMLHttpRequest) {
        req = new XMLHttpRequest();       
    // branch for IE/Windows ActiveX version
    } else if (window.ActiveXObject) {
      isIE = true;
      try {
      	req = new ActiveXObject("MSXML2.XMLHttp");
      } catch (e) {
      	try{ 	
         	req = new ActiveXObject("Microsoft.XMLHTTP");
       	}catch (E){
       		return false;
       	}    
      }            
    }
    if(isIE && req){      
    	req.onreadystatechange = processReqChange;
        req.open("GET", url, false);
        req.send();// Do not send null with IE        
    }    
    else if(!isIE && req){
    	req.onreadystatechange = processReqChange;
        req.open("GET", url, true);
        req.send(null);
    }else{
    	return 'DEGRADE_TO_URL';
    }
}

// handle onreadystatechange event of req object
function processReqChange() {
    // only if req shows "loaded"
    if (req.readyState == 4) {
        // only if "OK"
        if (req.status == 200) {
            clearRelevantPagePulldown();
            loadRelevantPagePulldown();
            req = null;
         } else {
            alert("There was a problem retrieving the XML data:\n" +
                req.statusText);
         }
    }   
}

// invoked by "Category" select element change;
// loads chosen XML document, clears Topics select
// element, loads new items into Topics select element
function loadDoc(evt) {
    // equalize W3C/IE event models to get event object
    evt = (evt) ? evt : ((window.event) ? window.event : null);
    if (evt) {
        // equalize W3C/IE models to get event target reference
        var elem = (evt.target) ? evt.target : ((evt.srcElement) ? evt.srcElement : null);
        if (elem) {
            try {
                if (elem.selectedIndex > 0) {
                    loadXMLDoc(elem.options[elem.selectedIndex].value, elem);
                }	
            }
            catch(e) {
                var msg = (typeof e == "string") ? e : ((e.message) ? e.message : "Unknown Error");
                alert("Unable to get XML data:\n" + msg);
                return;
            }
        }
    }
}

// retrieve text of an XML document element, including
// elements using namespaces
function getElementTextNS(prefix, local, parentElem, index) {
    var result = "";
    if (prefix && isIE) {
        // IE/Windows way of handling namespaces
        result = parentElem.getElementsByTagName(prefix + ":" + local)[index];
    } else {
        // the namespace versions of this method 
        // (getElementsByTagNameNS()) operate
        // differently in Safari and Mozilla, but both
        // return value with just local name, provided 
        // there aren't conflicts with non-namespace element
        // names
        result = parentElem.getElementsByTagName(local)[index];
    }
    if (result) {
        // get text, accounting for possible
        // whitespace (carriage return) text nodes 
        if (result.childNodes.length > 1) {
            return result.childNodes[1].nodeValue;
        } else {
            return result.firstChild.nodeValue;    		
        }
    } else {
        return "n/a";
    }
}

// empty Topics select list content
function clearRelevantPagePulldown() {
    var select = pulldownToPopulate;//document.fascimileForm.relevantPageSelector; 
                 
    while (select.length > 0) {
        select.remove(0);
    }
}

// add item to select element the less
// elegant, but compatible way.
function appendToSelect(select, value, content) {
    var opt;
    opt = document.createElement("option");
    opt.value = value;
    opt.appendChild(content);
    select.appendChild(opt);
}

// fill Topics select list with items from
// the current XML document
function loadRelevantPagePulldown() {
    
    var select = pulldownToPopulate;//document.fascimileForm.relevantPageSelector; ; 
    
    var items = req.responseXML.getElementsByTagName("pair");
    // loop through <item> elements, and add each nested
    // <title> element to Topics select element
    appendToSelect(select,"", document.createTextNode("Select Page")); //Add blank element.
    for (var i = 0; i < items.length; i++) {
    
    	var displayValue = getElementTextNS("", "name", items[i], 0);    	
    	if(displayValue == "-1"){
    		displayValue = "Next 30";
    	}
    	if(displayValue == "-2"){
    		displayValue = "Previous 30";
    	}

    	appendToSelect(select,getElementTextNS("", "value", items[i], 0),
            	document.createTextNode(displayValue));
    }
    // clear detail display
}