public static function add_order_item() {
		check_ajax_referer( 'order-item', 'security' );

		if ( ! current_user_can( 'edit_shop_orders' ) ) {
			wp_die( -1 );
		}

		$response = array();

		try {
			if ( ! isset( $_POST['order_id'] ) ) {
				throw new Exception( __( 'Invalid order', 'woocommerce' ) );
			}

			$order_id = absint( wp_unslash( $_POST['order_id'] ) ); // WPCS: input var ok.
			$order    = wc_get_order( $order_id );

			if ( ! $order ) {
				throw new Exception( __( 'Invalid order', 'woocommerce' ) );
			}

			// If we passed through items it means we need to save first before adding a new one.
			$items = ( ! empty( $_POST['items'] ) ) ? wp_unslash( $_POST['items'] ) : ''; // phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotSanitized

			if ( ! empty( $items ) ) {
				$save_items = array();
				parse_str( $items, $save_items );
				wc_save_order_items( $order->get_id(), $save_items );
			}

			$items_to_add = isset( $_POST['data'] ) ? array_filter( wp_unslash( (array) $_POST['data'] ) ) : array(); // phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotSanitized

			// Add items to order.
			$order_notes = array();

			foreach ( $items_to_add as $item ) {
				if ( ! isset( $item['id'], $item['qty'] ) || empty( $item['id'] ) ) {
					continue;
				}
				$product_id = absint( $item['id'] );
				$qty        = wc_stock_amount( $item['qty'] );
				$product    = wc_get_product( $product_id );

				if ( ! $product ) {
					throw new Exception( __( 'Invalid product ID', 'woocommerce' ) . ' ' . $product_id );
				}
				if ( 'variable' === $product->get_type() ) {
					/* translators: %s product name */
					throw new Exception( sprintf( __( '%s is a variable product parent and cannot be added.', 'woocommerce' ), $product->get_name() ) );
				}
				$validation_error = new WP_Error();
				$validation_error = apply_filters( 'woocommerce_ajax_add_order_item_validation', $validation_error, $product, $order, $qty );

				if ( $validation_error->get_error_code() ) {
					throw new Exception( '<strong>' . __( 'Error:', 'woocommerce' ) . '</strong> ' . $validation_error->get_error_message() );
				}
				$item_id                 = $order->add_product( $product, $qty );
				$item                    = apply_filters( 'woocommerce_ajax_order_item', $order->get_item( $item_id ), $item_id, $order, $product );
				$added_items[ $item_id ] = $item;
				$order_notes[ $item_id ] = $product->get_formatted_name();

				if ( $product->managing_stock() ) {
					$new_stock               = wc_update_product_stock( $product, $qty, 'decrease' );
					$order_notes[ $item_id ] = $product->get_formatted_name() . ' &ndash; ' . ( $new_stock + $qty ) . '&rarr;' . $new_stock;
					$item->add_meta_data( '_reduced_stock', $qty, true );
					$item->save();
				}

				do_action( 'woocommerce_ajax_add_order_item_meta', $item_id, $item, $order );
			}

			/* translators: %s item name. */
			$order->add_order_note( sprintf( __( 'Added line items: %s', 'woocommerce' ), implode( ', ', $order_notes ) ), false, true );

			do_action( 'woocommerce_ajax_order_items_added', $added_items, $order );

			$data = get_post_meta( $order_id );

			// Get HTML to return.
			ob_start();
			include 'admin/meta-boxes/views/html-order-items.php';
			$items_html = ob_get_clean();

			ob_start();
			$notes = wc_get_order_notes( array( 'order_id' => $order_id ) );
			include 'admin/meta-boxes/views/html-order-notes.php';
			$notes_html = ob_get_clean();

			wp_send_json_success(
				array(
					'html'       => $items_html,
					'notes_html' => $notes_html,
				)
			);
		} catch ( Exception $e ) {
			wp_send_json_error( array( 'error' => $e->getMessage() ) );
		}

		// wp_send_json_success must be outside the try block not to break phpunit tests.
		wp_send_json_success( $response );
	}