// This example shows how to subscribe to changes of a single item and display the value of the item with each change.
//
// Some related documentation: http://php.net/manual/en/function.com-event-sink.php . Pay attention to the comment that says 
// "Be careful how you use this feature; if you are doing something similar to the example below, then it doesn't really make 
// sense to run it in a web server context.". What they are trying to say is that processing a web request should be 
// a short-lived code, which does not fit well with the idea of being subscribed to events and received them over longer time. 
// It is possible to write such code, but it is only useful when processing the request is allowed to take relatively long. Or, 
// when you are using PHP from command-line, or otherwise - not to serve a web page directly.
// 
// Subscribing to QuickOPC-COM events in the context of PHP Web application, while not imposing the limitations to the request 
// processing time, has to be "worked around", e.g. using the "event pull" mechanism.

class DEasyDAClientEvents {
    function ItemChanged($varSender, $varE)
    {
        if ($varE->Succeeded)
        {
        print $varE->Vtq->ToString();
            print "\n";
        }
        else
        {
            printf("*** Failure: %s\n", $varE->ErrorMessageBrief);
        }
    }
}

$Client = new COM("OpcLabs.EasyOpc.DataAccess.EasyDAClient");
$Events = new DEasyDAClientEvents();
com_event_sink($Client, $Events, "DEasyDAClientEvents");

$Client->SubscribeItem("", "OPCLabs.KitServer.2", "Simulation.Random", 1000);

print "Processing item changed events for 1 minute...\n";
$startTime = time(); do { com_message_pump(1000); } while (time() < $startTime + 60);