prevent that items will be marked as exported if invoice can not be generated, check for existing invoice number to prevent that invalid invoices will be generated

src/Invoice/DuplicateInvoiceNumberException.php

@@ -0,0 +1,18 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Invoice;
+
+final class DuplicateInvoiceNumberException extends \Exception
+{
+    public function __construct(string $invoiceNumber)
+    {
+        parent::__construct('Invoice number "' . $invoiceNumber . '" already existing');
+    }
+}

src/Invoice/ServiceInvoice.php

@@ -366,12 +366,12 @@ final class ServiceInvoice
             if ($renderer->supports($document)) {
                 $dispatcher->dispatch(new InvoicePreRenderEvent($model, $document, $renderer));
 
-                $response = $renderer->render($document, $model);
-
-                if ($model->getQuery()->isMarkAsExported()) {
-                    $this->markEntriesAsExported($model->getEntries());
+                if ($this->invoiceRepository->hasInvoice($model->getInvoiceNumber())) {
+                    throw new DuplicateInvoiceNumberException($model->getInvoiceNumber());
                 }
 
+                $response = $renderer->render($document, $model);
+
                 $event = new InvoicePostRenderEvent($model, $document, $renderer, $response);
                 $dispatcher->dispatch($event);
 
@@ -382,6 +382,10 @@ final class ServiceInvoice
                 $invoice->setFilename($invoiceFilename);
                 $this->invoiceRepository->saveInvoice($invoice);
 
+                if ($model->getQuery()->isMarkAsExported()) {
+                    $this->markEntriesAsExported($model->getEntries());
+                }
+
                 $dispatcher->dispatch(new InvoiceCreatedEvent($invoice));
 
                 return $invoice;