I've done a few of these now. What worked best for me was putting ZF 'around' the old app, so all requests go through ZF. I then have a 'Legacy' controller plugin, which checks whether the request can be satisfied by ZF, and if not, sends it to the old app:
class Yourapp_Plugin_Legacy extends Zend_Controller_Plugin_Abstract
{
public function preDispatch(Zend_Controller_Request_Abstract $request)
{
$dispatcher = Zend_Controller_Front::getInstance()->getDispatcher();
if (!$dispatcher->isDispatchable($request)) {
// send to the old code...
}
}
}
exactly how you then send the request to your old app depends a bit on how it is implemented. In one project, I examined the request, determined what file from the old code the request would have gone to, and then required that in. It sounds like this might be appropriate for you. In another project my solution was to route all these requests to a LegacyController in the ZF project, which ran the old code to get the resulting HTML and then rendered it inside the Zend_Layout from the new project.
The advantages of this approach are that you can gradually introduce ZF modules as you rewrite parts of the old app, until you reach the point where 100% of requests can be served by ZF. Also, since the ZF project has initialized before your old code is run, your old code can use the ZF autoloader, so you can start replacing classes in the old code with models written in a more ZF-style, and have them used by both parts of the app.
