BUGS-5816: Resolves issue where changing file content would not serve…

… new files.

Contributors:
* [nsciacca](https://git.drupalcode.org/nsciacca)
* [Ec1ipsis](https://git.drupalcode.org/Ec1ipsis)

pantheon_advanced_page_cache.module

@@ -0,0 +1,32 @@
+<?php
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\image\Entity\ImageStyle;
+
+/**
+ * Implements hook_ENTITY_TYPE_update() for file entities.
+ *
+ * Clears edge cache by file url. If this is not done, changing file contents
+ * does not actually change the file that gets served until the cache times out.
+ */
+function pantheon_advanced_page_cache_file_update(EntityInterface $file) {
+  // Don't try this if we're not in a Pantheon environment.
+  if (function_exists('pantheon_clear_edge_paths')) {
+    // No matter what, the file's base URL needs to be cleared out .
+    $paths_to_clear = [$file->createFileUrl()];
+
+    // If this is an image, we need to clear the edge cache paths for every
+    // image style, or those won't work.
+    if (strpos($file->getMimeType(), 'image', 0) === 0) {
+      $styles = ImageStyle::loadMultiple();
+      foreach ($styles as $style) {
+        $file_uri = $file->getFileUri();
+        $url      = $style->buildUrl($file_uri);
+
+        $paths_to_clear[] = parse_url($url)['path'];
+      }
+    }
+
+    pantheon_clear_edge_paths($paths_to_clear);
+  }
+}