/** \file comet_statusupdates.js
 *  \brief File containing all functions to handle ZKL status updates through a COMET/JSON link
 *  \author Bart van Hest, Core|Vision
 *  \version 1.0
 *  \date 20-10-2008
 *	\todo 
 *
 * This file contains the functions needed to perform 'real-time' status updates for the ZKL through a COMET/JSON link.
 * It works by opening a connection to a blocking PHP script using the XMLHttpRequest object. The PHP
 * script must block as long as no status updates are available. When a status update is available,
 * it should spit out JScript code which can be evaluated using eval(). This code should fill in
 * an array of objects named ZKL_Status, with members of the object named s_<name>.
 * 
 * The code does only a simple header check to find out if the data send by PHP is valid. The
 * header should be ZKLsu1.0 in slash-star comment, which stands for ZKL Status Update v1.0
 * 
 * After eval(), the Array should look like this:
 *    ZKL_Status[0]
 *        s_param1 : "param1 value"
 *        s_param2 : "param2 value"
 *    ZKL_Status[1]
 *        s_param1 : "param1 value"
 *        s_param2 : "param2 value"
 *    ..
 *    ZKL_Status[n]
 *        s_param1 : "param1 value"
 *        s_param2 : "param2 value"
 *
 * Also, the Array sent should contain information for all ZKLs monitored, not only the updated ones.
 */

var ZKL_Status = null;				// The array with new ZKL status information returned during an update
var xmlhttp = null;					// The XMLHttpRequest object used to get status updates
var TimeOut = null;                 // our timeout counter. We can't add this to the xmlhttp object; IE won't let us. #@$^#$ browser :(
var DataRdyCallback = null;         // The callback which should handle new data
var DataErrorCallback = null;       // The callback which should handle an error in the data
var ProjectID = -1;                 // Our project ID for which to ask status updates
var LastRequestTime = -1;           // The time our last request was made. Used to discriminate between intentional and unintentional timeouts`
var Sequence = 0                    // Add sequence to be unique and disable cache
var ValidRequestTime = -1;          // The time our last request was valid. Used to discriminate between intentional and unintentional timeouts
var CometServerScriptURL = null;    // The URL of our COMET dataserver script.

var TimeOutmSecs = 12000;           // our timeout in milliseconds


/**
 * Default data-error callback.
 * 
 * This default callback crates an empty ZKL_Status() array and calls the DataRdyCallback.
 * This causes all devices to simply disappear from the screen
 */
function defErrorCallback() {
    DbgPrint ("Default data-error callback called.");
    ZKL_Status = [];
    if (DataRdyCallback != null) { DataRdyCallback(); }
} 


/**
 *  Create the XMLHttpRequest object
 *
 *  Inputs:
 *  - fnDataRdyCallback:    A callback which is called when new statusinfo is received.
 *  - fnDataErrorCallback:  A callback which is called when an error occurred during data reception.
 *  - sesson_id:            A number which make this a unique session
  */
function createUpdater(fnDataRdyCallback, fnDataErrorCallback, sessionid) {
    DbgPrint ("createUpdater()");
    OurURL = document.URL;
    DocRoot = OurURL.split('?');
    CometServerScriptURL = DocRoot[0]+"index.php?redirect=scripts/other/rtstatus_datapump.php&id="+sessionid+"&extra_path=../../";
    DbgPrint ("COMET server URL: "+CometServerScriptURL);
    
    // Create the XMLHttpRequest object in a browser-independent way
    try {
        xmlhttp = new XMLHttpRequest();
    } 
    catch (e) {
        try {
            xmlhttp = new ActiveXObject('Msxml2.XMLHTTP');
        } 
        catch (e) {
            try {
                xmlhttp = new ActiveXObject('Microsoft.XMLHTTP');
            } 
            catch (e) {
                xmlhttp = null;
            }
        }
    }
    if (!xmlhttp && window.createRequest) {
        try {
		    xmlhttp = window.createRequest();
		} catch (e) {
			xmlhttp=null;
		}
	}
	
	if (typeof(fnDataRdyCallback) != 'undefined') {
        DataRdyCallback = fnDataRdyCallback;
    } 
    else {
        DbgPrint ("INTERNAL ERROR: No DataReadyCallback passed");
    }

    if (typeof(fnDataErrorCallback) != 'undefined' && fnDataErrorCallback != null) {
        DataErrorCallback = fnDataErrorCallback;
    } 
    else {
        // default error callback
        DataErrorCallback = defErrorCallback;
        DbgPrint ("No valid error callback given; reverting to default error callback..");
    }
    
    // Start the first request
    xmlhttp_startrequest(true);
}


/**
 *  Abort & destroy the updater.
 *
 *  Inputs:
 *     none.
  */
function AbortUpdater() {
    DataErrorCallback = null;
    if (xmlhttp!=null) {
        // Assign an empty function to the state handler; IE doesn't like setting this to null.
        xmlhttp.onreadystatechange = function () {}
        // Abort current transfer. This will also call the state handler, which is not what we want
        xmlhttp.abort();
        // Clear object
        xmlhttp = null;
    }
}


/**
  * Handle a timeout on the xmlhttp request
  */
function xmlhttp_Timeout() {    
    try {
        DbgPrint ("XMLHttpRequest timed out. Restarting...");    
        // Assign an empty function to the state handler; IE doesn't like setting this to null.
        xmlhttp.onreadystatechange = function () {}
        // Abort the current status transfer
        xmlhttp.abort();

        // See if we need to call the data error callback
        if ((new Date().getTime() - LastRequestTime) > TimeOutmSecs) {            
            if (DataErrorCallback != null) {
                DataErrorCallback();
            }
        }
    }
    catch (ex) {
        // Silent exception        
    }           
    finally {   
        // And start a new one (this will also re-initialise the state handler)
        xmlhttp_startrequest();
   }
}


/**
 * Start a request for status updates.
 *
 * Inputs:
 *  - bFirstTime:           A boolean indicating whether this is the first time we
 *                          request data. The first time we need data immediately,
 *                          subsequent requests may be stalled until there is new data
 *                          available.
 */
function xmlhttp_startrequest(bFirstTime) {
    // Check the arguments
    bFirstTime = typeof(bFirstTime) == 'boolean' ? bFirstTime : false;  
    // start the XHR request
    if (xmlhttp!=null) {
        // We put a timeout on this request. Restarting the status updater script once in a while
        // is not a bad idea since some Web-servers won't allow a script to run for a long time.
        TimeOut = setTimeout("xmlhttp_Timeout();",TimeOutmSecs+250);
        // Remember the current times so we know when a timeout was unintentional or not.
        LastRequestTime = new Date().getTime();        
        if (ValidRequestTime == -1) {
          ValidRequestTime = new Date().getTime();
        }
        xmlhttp.onreadystatechange=xmlhttp_statechange;        
        xmlhttp.open("GET",CometServerScriptURL+"&Seq="+(Sequence++)+"&blocking="+(bFirstTime?'false':'true'),true);
        xmlhttp.send(null);
    }
}


/**
 * Data-present function which is called when new ZKL data arrives
 */
function xmlhttp_statechange() {
	// Do we have an update from the server? => Else still in progress
    if (xmlhttp.readyState == 4) {       
        try {
            // Cancel settimeout
            clearTimeout(TimeOut);        
            
            if (xmlhttp.status == 200 ) {
                // Reset timeout
                ValidRequestTime = new Date().getTime();        
                
                // Do something with the data. Check our 'magic-ID'. If it passes,                                               
                var offset = xmlhttp.responseText.search("\/[*]ZKLsu1.0[*]\/");
                    
                // Magic code available?                    
                if (offset != -1) {                    
                    //DbgPrint(xmlhttp.responseText);
                	eval(xmlhttp.responseText.substring(offset));
                	                
                	// OK, by now we should have a ZKL_Status array with statuses of devices in the field.
                	// Call the user supplied callback
                	if (DataRdyCallback != null) {
                	    DataRdyCallback();
                	}
                	// We had a valid request, so no DataErrorCallback may be called, so clear LastRequestTime
                	LastRequestTime = new Date().getTime();                        	
                } 
                else {                            
             	    DbgPrint("Invalid data from server\n("+xmlhttp.responseText+")");
                	// Call our data error callback
                	if (DataErrorCallback != null) {
                	    DataErrorCallback();
                	}
                }
            } 
            else if ((xmlhttp.status == 0) || (xmlhttp.status == 12029) || (xmlhttp.status == 12007)) {
                // Catch IE/FF exceptions when no connection available
                if ((new Date().getTime() - ValidRequestTime) > TimeOutmSecs) {
                    DbgPrint ("XMLHttpRequest FF timed out, status 0. Calling DataErrorCallback()..");    
                    if (DataErrorCallback != null) {
                        DataErrorCallback();
                    }
                }                
            } 
            else {
                // Our request failed. Call the data error callback
                DbgPrint ("xmlhttp_status: "+xmlhttp.status);            
            }  
        }
        catch(ex) { 
            // Silent exception            
        }          
        finally {
           // Redo request.                                
           // We used to do a xmlhttp_startrequest() again. This works in every browser, except IE.
           // IE won't allow us to call XMLHttpRequest methods from within the event handler.
           // So, we use a hack: we shorten the timeout to 250msec. Once we have a timeout, a new
           // request will be started.
           TimeOut = setTimeout("xmlhttp_Timeout();",250);                
        }
	}
}