public function sell($productId, $amount) { $productModel = new ProductModel(); $viewModel = new InformationViewModel(); if (!$productModel->exists($productId)) { $viewModel->error = "Product {$productId} does not exist"; return new View($viewModel); } if ($amount < 0) { $viewModel->error = "You can sell at least one item"; return new View($viewModel); } try { $productModel->sell($_SESSION['id'], $productId, $amount); $viewModel->success = "Product {$productId} sold successfully"; } catch (\Exception $e) { $viewModel->error = $e->getMessage(); } return new View($viewModel); }