Issue #3506812: Add generic handling of JSON:API includes

Closes #3506812

src/Plugin/ExternalEntities/StorageClient/JsonApi.php

@@ -67,7 +67,7 @@ class JsonApi extends RestClient {
       ],
       'response_format' => [
         '#type' => 'hidden',
-        '#default_value' => 'json',
+        '#default_value' => 'external_entities_api_json',
       ],
       'data_path' => [
         'list' => [
@@ -91,7 +91,7 @@ class JsonApi extends RestClient {
       ],
       'pager' => [
         '#type' => NULL,
-        // Drupal uses a 50 elements per bage basis so we go for 1 query per
+        // Drupal uses a 50 elements per page basis so we go for 1 query per
         // page. 50 is the JSON:API default limit anyway.
         'default_limit' => [
           '#type' => 'hidden',
@@ -348,16 +348,49 @@ class JsonApi extends RestClient {
 
     $result = parent::load($id);
 
-    // Check for "included".
-    if (!empty($result[1])) {
-      // JSONPath returned an array of object so we got "extra" from "included".
-      $included = array_slice($result, 1);
-      $result = $result[0];
-      $result['included'] = $included;
-    }
     static::$cachedData[$this->configuration['endpoint']][$id] = $result;
 
     return $result;
   }
 
+  protected function resolveRelationships(&$result): void
+  {
+    // Collect all includes and index them by type and id.
+    $includedRegistry = [];
+    foreach ($result['included'] as $included_entry) {
+      $included_id = ($included_entry['type'] ?? NULL) . ':' . $included_entry['id'];
+      $includedRegistry[$included_id] = $included_entry;
+    }
+    $this->_resolveRelationsRecursive($result['relationships'], $includedRegistry);
+  }
+
+  protected function _resolveRelationsRecursive(&$relationships, $includedRegistry): void
+  {
+    foreach ($relationships as $field => $relationship) {
+      if (!empty($relationship['data'])) {
+        // Relationships can be single or multi-value.
+        if (isset($relationship['data']['id'])) {
+          $this->_mapRelationshipData($relationships[$field]['data'], $includedRegistry);
+        } else {
+          foreach ($relationship['data'] as $i => $data) {
+            $this->_mapRelationshipData($relationships[$field]['data'][$i], $includedRegistry);
+          }
+        }
+      }
+    }
+  }
+
+  protected function _mapRelationshipData(&$data, array $includedRegistry): void
+  {
+    if (isset($data['id'])) {
+      $included_id = ($data['type'] ?? NULL) . ':' . $data['id'];
+      if (isset($includedRegistry[$included_id])) {
+        $data['included'] = $includedRegistry[$included_id];
+      }
+      if (!empty($data['relationships'])) {
+        $this->_resolveRelationsRecursive($data['relationships'], $includedRegistry);
+      }
+    }
+  }
+
 }