Add validation for when feedname already exists

Author: martialblog

application/forms/FeedForm.php

@@ -52,9 +52,15 @@ protected function assemble(): void
                         $validator->addMessage($this->translate('The name must only contain alphanumeric characters'));
                         return false;
                     }
-
                     return true;
-                })
+                }),
+                new CallbackValidator(function (string $value, CallbackValidator $validator) {
+                    if ($this->storage->getFeedByName($value) !== null) {
+                        $validator->addMessage($this->translate(sprintf("A feed with the name %s already exists", $value)));
+                        return false;
+                    }
+                    return true;
+                }),
             ],
         ]);