Move wisski instance code to separate package

internal/wisski/php/list_uri_prefixes.php

@@ -0,0 +1,51 @@
+<?php
+
+/**
+ * list_prefixes lists all content prefixes known to this WissKI.
+ * Prefixes are not filtered, and may contain duplicates.
+ */ 
+function list_prefixes() {
+    $prefixes = [];
+    $storage = \Drupal::entityTypeManager()->getStorage('wisski_salz_adapter');
+    foreach ($storage->loadMultiple() as $adapter) {
+        // load all the prefixes from the triplestore
+        $engine = $adapter->getEngine();
+        getTriplestorePrefixes($adapter->getEngine(), $prefixes);
+
+        // read the configuration to check if we have a default graph
+        $conf = $engine->getConfiguration();
+        if(!array_key_exists('default_graph', $conf)) {
+            continue;
+        }
+        $prefixes[] = $conf['default_graph'];
+    }
+    return $prefixes;
+}
+
+function getTriplestorePrefixes($engine, &$prefixes) {
+    // some adapters don't support a query method!
+    if (!method_exists($engine, 'directQuery')) return NULL;
+
+    $results = $engine->directQuery('
+    select distinct ?base where {
+        {
+            select distinct ?iri where {
+                {
+                    select distinct (?s as ?iri) { ?s ?p ?o  }
+                } union {
+                    select distinct (?o as ?iri) { ?s ?p ?o FILTER(isiri(?o)) }
+                }
+            }  
+        }
+        BIND(replace(str(?iri), "/[^/]*/?$", "/") as ?base)
+        FILTER(!REGEX(?base, "/wisski/navigate/[\\\\d]+/$"))
+    } ORDER BY ?base');
+    if (!$results) return FALSE;
+
+    foreach($results as $result) {
+        $prefixes[] = $result->base->getValue();
+    }
+
+    return TRUE;
+} 
+