Disallow fetching from Wikidata disambiguation pages

Close #23

src/NodaWikidataFetcher.php

@@ -178,7 +178,20 @@ final class NodaWikidataFetcher {
         if (empty($data['entities'][$wikidata_id])) {
             throw new MDhttpFailedException("Failed fetching from Wikidata. Try again later.");
         }
-        return $data['entities'][$wikidata_id];
+
+        $output = $data['entities'][$wikidata_id];
+
+        // Throw exception if this page is a dedicated disambigation item.-
+        // P31: Instance of; Q4167410: Wikimedia disambiguation page
+        if (isset($output['claims']) && isset($output['claims']['P31'])) {
+            foreach ($output['claims']['P31'] as $is_instance_of) {
+                if (isset($is_instance_of['mainsnak']['datavalue']['value']['id']) && $is_instance_of['mainsnak']['datavalue']['value']['id'] === 'Q4167410') {
+                    throw new NodaWikidataFetcherDisambiguationIsDisallowedException("Loading wikidata disambiguation pages is disallowed");
+                }
+            }
+        }
+
+        return $output;
 
     }
 

src/NodaWikidataFetcherDisambiguationIsDisallowedException.php

@@ -0,0 +1,27 @@
+<?PHP
+/**
+ * This file contains an exception class to be thrown if a user attempts to load
+ * data from a Wikidata item specifically established for a disambiguation page.
+ *
+ * @file
+ *
+ * @author Joshua Ramon Enslin <joshua@museum-digital.de>
+ */
+declare(strict_types = 1);
+
+/**
+ * Exception class to be thrown if a user attempts to load
+ * data from a Wikidata item specifically established for a disambiguation page.
+ */
+final class NodaWikidataFetcherDisambiguationIsDisallowedException extends MDgenericInvalidInputsException {
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        return 'Attempted to load a disambiguation page. Please select the specific item you want to fetch to enrich the given entry: ' . $this->getMessage();
+
+    }
+}