feat[indexes]: add inverted index implementation

Author: lucassouzavieira

src/Collection/Index/Factory.php

@@ -62,6 +62,10 @@ public static function factory(array $attributes): IndexInterface
             return new TTLIndex($attributes['fields'], $attributes['expireAfter'], $attributes);
         }
 
+        if ($attributes['type'] === 'inverted') {
+            return new InvertedIndex($attributes['fields'], $attributes);
+        }
+
         $class = $indexes[$attributes['type']];
         return new $class($attributes['fields'], $attributes);
     }

src/Collection/Index/Index.php

@@ -85,7 +85,7 @@ class Index implements IndexInterface
     /**
      * Index constructor.
      *
-     * @param string $type The index type. Must be one of following values: 'fulltext', 'general', 'geo', 'hash', 'persistent', 'skiplist' or 'ttl'
+     * @param string $type The index type. Must be one of following values: 'fulltext', 'general', 'geo', 'hash', 'persistent', 'skiplist', 'inverted' or 'ttl'
      * @param array $fields An array of attribute names. Normally with just one attribute.
      *
      * @param array $attributes
@@ -97,10 +97,20 @@ public function __construct(string $type, array $fields, array $attributes = [])
             throw new InvalidParameterException("type", $type);
         }
 
+        $fieldNames = [];
+
         foreach ($fields as $key => $field) {
-            if (!is_string($field)) {
-                throw new InvalidParameterException("fields[$key]", $field);
+            if (is_string($field)) {
+                array_push($fieldNames, $field);
+                continue;
+            }
+
+            if (is_array($field)) {
+                array_push($fieldNames, $field['name']);
+                continue;
             }
+
+            throw new InvalidParameterException("fields[$key]", $field);
         }
 
         $this->type = $type;

src/Collection/Index/InvertedIndex.php

@@ -10,8 +10,21 @@
 * @package ArangoDB\Collection\Index
 * @author Lucas S. Vieira
 */
-class InvertedIndex extends Index
+final class InvertedIndex extends Index
 {
+    /**
+     * Default options for inverted index
+     *
+     * @var array
+     */
+    protected array $defaultOptions = [
+        'unique' => true,
+        'sparse' => true,
+        'analyzer' => "identity",
+        'inBackground' => true, // Keep the collection available for writes during the index creation
+        'parallelism' => 2,
+    ];
+
     /**
      * InvertedIndex constructor
      *