Start thinking to roll in more cache headers; however, shouldn't be n…

…ecessary.

embargo.services.yml

@@ -31,3 +31,7 @@ services:
       - '@url_generator'
     tags:
       - { name: 'event_subscriber' }
+  embargo.search_api.pre_execute_subscriber:
+    class: Drupal\embargo\EventSubscriber\ViewsCacheEventSubscriber
+    tags:
+      - { name: 'event_subscriber' }

src/EventSubscriber/ViewsCacheEventSubscriber.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace Drupal\embargo\EventSubscriber;
+
+use Drupal\Core\Cache\RefinableCacheableDependencyInterface;
+use Drupal\search_api\Event\QueryPreExecuteEvent;
+use Drupal\search_api\Event\SearchApiEvents;
+use Drupal\search_api\Query\QueryInterface;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * Views cache event subscriber implementation.
+ */
+class ViewsCacheEventSubscriber implements EventSubscriberInterface {
+
+  /**
+   * {@inheritDoc}
+   */
+  public static function getSubscribedEvents() {
+    return [
+      SearchApiEvents::QUERY_PRE_EXECUTE => 'preExecute',
+      //'search_api.query_pre_execute.alter_cache_metadata' => ['alterCacheMetadata'],
+    ];
+  }
+
+  public function preExecute(QueryPreExecuteEvent $event) {
+    dsm($event->getQuery()->getTags());
+    if ($event->getQuery()->hasTag('alter_cache_metadata')) {
+      $this->alterCacheMetadata($event);
+    }
+
+    $query = $event->getQuery();
+    if ($query instanceof RefinableCacheableDependencyInterface) {
+      dsm($query->getCacheContexts());
+      dsm($query->getCacheTags());
+      dsm($query->getCacheMaxAge());
+    }
+  }
+
+  /**
+   * Alter cache metadata.
+   *
+   * @param \Drupal\search_api\Event\QueryPreExecuteEvent $event
+   *   The pre-execution event.
+   */
+  public function alterCacheMetadata(QueryPreExecuteEvent $event) : void {
+    $query = $event->getQuery();
+    if (!($query instanceof RefinableCacheableDependencyInterface)) {
+      dsm('blah');
+      // Cannot add metadata to it.
+      return;
+    }
+    if ($this->containsRelevantIndex($query)) {
+      //$query->add
+    }
+  }
+
+  protected function containsRelevantIndex(QueryInterface $query) : bool {
+    dsm($query->getTags());
+    return FALSE;
+  }
+
+}