Moved logic to generate random short codes to external function

module/Core/functions/functions.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\Core;
+
+use PUGX\Shortid\Factory as ShortIdFactory;
+
+function generateRandomShortCode(int $length = 5): string
+{
+    static $shortIdFactory;
+    if ($shortIdFactory === null) {
+        $shortIdFactory = new ShortIdFactory();
+    }
+
+    $alphabet = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
+    return $shortIdFactory->generate($length, $alphabet)->serialize();
+}