Billing Import button disables all elements

Layout/default/Billing/Index.php

@@ -112,9 +112,10 @@ $pagination_entity_name = "Billingrecords";
                                 <!--button type="submit" class="btn btn-primary"><i class="fas fa-fw fa-check"></i> Markierte Elemente als Contract übernehmen</button-->
                             </div>
                             <div class="float-right">
-                                <a class="btn btn-outline-primary mb-2" href="<?=self::getUrl("Billing", "importContracts")?>">
+                                <button class="btn btn-outline-primary mb-2" onclick="startBilling(event)">
                                     <i class="fas fa-fw fa-file-import"></i> Rechnungsdatensätze aus Contracts erstellen
-                                </a>
+                                </button>
+                                <img src="img/ajax-loader.gif" class="float-right mr-2 hidden" id="billing-loader" />
                             </div>
                         </div>
                     </div>
@@ -249,5 +250,19 @@ $pagination_entity_name = "Billingrecords";
         todayBtn: 'linked',
         autoclose: true
     });
+
+    function startBilling(e) {
+        e.preventDefault();
+
+        if(!confirm("Wirklich Billinglauf starten?")) {
+            return false;
+        }
+
+        $('button, input').prop('disabled', true);
+        $('a').removeAttr("href");
+        $("#billing-loader").show();
+        window.location.href = "<?=self::getUrl("Billing", "importContracts")?>";
+        return false;
+    }
 </script>
 <?php include(realpath(dirname(__FILE__) . "/../../$mfLayoutPackage") . "/footer.php"); ?>