Issue with intercepting 404s and render another page based on URL

[Jonathan Lahijani]

I'm trying to intercept a 404 error page and have it render another page based on some general logic:

The following is in /site/init.php:

$this->addHookBefore('ProcessPageView::pageNotFound', function($event) {
  $url = $event->arguments('url');
  
  // ensure trailing slashes
  if($url[-1] !== "/") $this->session->redirect(substr(wire("config")->urls->root, 0, -1).$url."/");

  $p = wire('pages')->get("/sites/".wire('config')->site.$url);
  if($p->id) {
    $event->replace = true;
    $event->return = $p->render();
  } else {
    $event->replace = false;
  }

});

Given my setup, $p->render() will cause an error related to it not finding a custom function I have defined in my /site/templates/_init.php:

Call to undefined function myWeirdFunction() 

How do I properly render the file and make sure the chain of included files is correct?  This is always a little confusing to me.

[adrian]

Maybe something useful in here?
https://github.com/adrianbj/ProcessRedirectIds/blob/master/ProcessRedirectIds.module