Atomic tenant creation

src/Contracts/StorageDriver.php

@@ -29,4 +29,12 @@ interface StorageDriver
      * @return Tenant
      */
     public function findByDomain(string $domain): Tenant;
+
+    /**
+     * Check if a tenant can be created.
+     *
+     * @param Tenant $tenant
+     * @return true|TenantCannotBeCreatedException
+     */
+    public function canCreate(Tenant $tenant);
 }

src/Contracts/TenantCannotBeCreatedException.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace Stancl\Tenancy\Contracts;
+
+abstract class TenantCannotBeCreatedException extends \Exception
+{
+    abstract function reason(): string;
+
+    private $message;
+
+    public function __construct()
+    {
+        $this->message = 'Tenant cannot be craeted. Reason: ' . $this->reason();
+    }
+}