Issue #3253964 by Luke.Leber: Add a css pre-render event dispatch

inline_all_css.services.yml

@@ -5,3 +5,4 @@ services:
     decorates: asset.css.collection_renderer
     arguments:
       - '@file_system'
+      - '@event_dispatcher'

src/Asset/CriticalCssCollectionRenderer.php

@@ -5,6 +5,8 @@ namespace Drupal\inline_all_css\Asset;
 use Drupal\Core\Asset\AssetCollectionRendererInterface;
 use Drupal\Core\File\FileSystemInterface;
 use Drupal\Core\Render\Markup;
+use Drupal\inline_all_css\Event\CssPreRenderEvent;
+use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use function file_get_contents;
 
 /**
@@ -21,14 +23,24 @@ class CriticalCssCollectionRenderer implements AssetCollectionRendererInterface
    */
   protected $fileSystem;
 
+  /**
+   * The event dispatcher service.
+   *
+   * @var \Symfony\Component\EventDispatcher\EventDispatcherInterface
+   */
+  protected $eventDispatcher;
+
   /**
    * Constructs a CriticalCssCollectionRenderer.
    *
    * @param \Drupal\Core\File\FileSystemInterface $file_system
    *   The file system service.
+   * @param \Symfony\Component\EventDispatcher\EventDispatcherInterface $event_dispatcher
+   *   The event dispatcher service.
    */
-  public function __construct(FileSystemInterface $file_system) {
+  public function __construct(FileSystemInterface $file_system, EventDispatcherInterface $event_dispatcher) {
     $this->fileSystem = $file_system;
+    $this->eventDispatcher = $event_dispatcher;
   }
 
   /**
@@ -41,6 +53,11 @@ class CriticalCssCollectionRenderer implements AssetCollectionRendererInterface
       $css .= file_get_contents($file);
     }
 
+    $event = new CssPreRenderEvent($css);
+    /* @noinspection PhpMethodParametersCountMismatchInspection */
+    $this->eventDispatcher->dispatch($event, CssPreRenderEvent::EVENT_NAME);
+    $css = $event->getCss();
+
     return [
       [
         '#type' => 'html_tag',

src/Event/CssPreRenderEvent.php

+<?php
+
+namespace Drupal\inline_all_css\Event;
+
+use Drupal\Component\EventDispatcher\Event;
+
+/**
+ * Event that is fired before css is rendered.
+ */
+class CssPreRenderEvent extends Event {
+
+  public const EVENT_NAME = 'inline_all_css_css_pre_render';
+
+  /**
+   * The css string that is about to be rendered.
+   *
+   * @var string
+   */
+  protected $css;
+
+  /**
+   * Creates a new css pre-render event.
+   *
+   * @param string $css
+   *   The initial css of the event.
+   */
+  public function __construct($css) {
+    $this->css = $css;
+  }
+
+  /**
+   * Gets the css string for this event.
+   *
+   * @return string
+   *   The css string for this event.
+   */
+  public function getCss() {
+    return $this->css;
+  }
+
+  /**
+   * Sets the css string for this event.
+   *
+   * @param string $css
+   *   The CSS string to set.
+   */
+  public function setCss($css) {
+    $this->css = $css;
+  }
+
+}

tests/src/Unit/CssCollectionRendererTest.php

@@ -5,7 +5,9 @@ namespace Drupal\Tests\inline_all_css\Unit;
 use Drupal\Core\File\FileSystemInterface;
 use Drupal\Core\Render\Markup;
 use Drupal\inline_all_css\Asset\CriticalCssCollectionRenderer;
+use Drupal\inline_all_css\Event\CssPreRenderEvent;
 use Drupal\Tests\UnitTestCase;
+use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 
 /**
  * Test cases for the critical css collection renderer.
@@ -37,7 +39,23 @@ class CssCollectionRendererTest extends UnitTestCase {
         ['public://test-2.css', __DIR__ . '/../../fixtures/test-2.css'],
         ['public://test-3.css', __DIR__ . '/../../fixtures/test-3.css'],
       ]);
-    $this->instance = new CriticalCssCollectionRenderer($filesystem);
+
+    $eventDispatcher = $this->getMockBuilder(EventDispatcherInterface::class)
+      ->disableOriginalConstructor()
+      ->getMock();
+
+    $eventDispatcher->method('dispatch')
+      ->willReturnCallback(static function (CssPreRenderEvent $event) {
+        $css = $event->getCss();
+        $css .= <<<CSS
+.event {
+  color: gray;
+}
+CSS;
+        $event->setCss($css);
+      });
+
+    $this->instance = new CriticalCssCollectionRenderer($filesystem, $eventDispatcher);
   }
 
   /**
@@ -64,7 +82,9 @@ html {
 body {
   color: blue;
 }
-
+.event {
+  color: gray;
+}
 CSS),
       ],
     ];

tests/src/Unit/CssPreRenderEventTest.php

+<?php
+
+namespace Drupal\Tests\inline_all_css\Unit;
+
+use Drupal\inline_all_css\Event\CssPreRenderEvent;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Test cases for the css pre-render event.
+ *
+ * @group inline_all_css
+ */
+class CssPreRenderEventTest extends UnitTestCase {
+
+  /**
+   * Test case for the css pre-render event.
+   */
+  public function testCssPreRenderEvent() {
+    $event = new CssPreRenderEvent('* { color: red; }');
+    static::assertSame('* { color: red; }', $event->getCss());
+
+    $new_css = 'html { color: green; }';
+    $event->setCss($new_css);
+    static::assertSame($new_css, $event->getCss());
+  }
+
+}