Render a Twig expression over an HTML string - php

Question

This could sound a bit weird, but this is a special situation:
I have an HTML string in $content, and I want to render a stylesheet block in the head tag of this content. This is what I have:
$response = new Response();
$response->setContent($content);
$response->headers->set('Content-Type', 'text/html');
// returns the HTTP headers followed by the content
return $response;
and I want to add:
{% stylesheets output='compiled/css/*.css' 'css/all.less' %}
<link rel="stylesheet" href="{{ asset_url }}" />
{% endstylesheets %}
Any idea of how could achieve it?
Edit:
As #CarlMarkham suggested, I tried:
$loader = new \Twig_Loader_Array(array(
'index.html' => $content."{% stylesheets output='compiled/css/*.css' 'css/all.less' %}
<link rel='stylesheet' href='{{ asset_url }}' />
{% endstylesheets %}",
));
$twig = new \Twig_Environment($loader);
return $twig->render('index.html');
but I got this error:
Unknown tag name "stylesheets" in index.html
Also tried this:
$loader = new \Twig_Loader_Array(array(
'index.html' => $content.'<link rel="stylesheet" href="{{ asset("compiled/css/*.css") }}">'
));
$twig = new \Twig_Environment($loader);
return $twig->render('index.html');
but I got:
The function "asset" does not exist in index.html

Answer 1

Take a look at Assetic. You should be able to build the html from within php (first code block click on the php tag). That example is for JS but it is the same concept for CSS. Now you have the string you can add it to the content.