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    <h3>Editing: CartAddItem.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php
namespace Automattic\WooCommerce\StoreApi\Routes\V1;

use Automattic\WooCommerce\StoreApi\Exceptions\RouteException;

/**
 * CartAddItem class.
 */
class CartAddItem extends AbstractCartRoute {
	/**
	 * The route identifier.
	 *
	 * @var string
	 */
	const IDENTIFIER = 'cart-add-item';

	/**
	 * Get the path of this REST route.
	 *
	 * @return string
	 */
	public function get_path() {
		return self::get_path_regex();
	}

	/**
	 * Get the path of this rest route.
	 *
	 * @return string
	 */
	public static function get_path_regex() {
		return '/cart/add-item';
	}

	/**
	 * Get method arguments for this REST route.
	 *
	 * @return array An array of endpoints.
	 */
	public function get_args() {
		return [
			[
				'methods'             =&gt; \WP_REST_Server::CREATABLE,
				'callback'            =&gt; [ $this, 'get_response' ],
				'permission_callback' =&gt; '__return_true',
				'args'                =&gt; [
					'id'        =&gt; [
						'description'       =&gt; __( 'The cart item product or variation ID.', 'woocommerce' ),
						'type'              =&gt; 'integer',
						'context'           =&gt; [ 'view', 'edit' ],
						'sanitize_callback' =&gt; 'absint',
					],
					'quantity'  =&gt; [
						'description' =&gt; __( 'Quantity of this item to add to the cart.', 'woocommerce' ),
						'type'        =&gt; 'integer',
						'context'     =&gt; [ 'view', 'edit' ],
						'arg_options' =&gt; [
							'sanitize_callback' =&gt; 'wc_stock_amount',
						],
					],
					'variation' =&gt; [
						'description' =&gt; __( 'Chosen attributes (for variations).', 'woocommerce' ),
						'type'        =&gt; 'array',
						'context'     =&gt; [ 'view', 'edit' ],
						'items'       =&gt; [
							'type'       =&gt; 'object',
							'properties' =&gt; [
								'attribute' =&gt; [
									'description' =&gt; __( 'Variation attribute name.', 'woocommerce' ),
									'type'        =&gt; 'string',
									'context'     =&gt; [ 'view', 'edit' ],
								],
								'value'     =&gt; [
									'description' =&gt; __( 'Variation attribute value.', 'woocommerce' ),
									'type'        =&gt; 'string',
									'context'     =&gt; [ 'view', 'edit' ],
								],
							],
						],
					],
				],
			],
			'schema'      =&gt; [ $this-&gt;schema, 'get_public_item_schema' ],
			'allow_batch' =&gt; [ 'v1' =&gt; true ],
		];
	}

	/**
	 * Handle the request and return a valid response for this endpoint.
	 *
	 * @throws RouteException On error.
	 * @param \WP_REST_Request $request Request object.
	 * @return \WP_REST_Response
	 */
	protected function get_route_post_response( \WP_REST_Request $request ) {
		// Do not allow key to be specified during creation.
		if ( ! empty( $request['key'] ) ) {
			throw new RouteException( 'woocommerce_rest_cart_item_exists', esc_html__( 'Cannot create an existing cart item.', 'woocommerce' ), 400 );
		}

		/**
		 * Filters cart item data sent via the API before it is passed to the cart controller.
		 *
		 * This hook filters cart items. It allows the request data to be changed, for example, quantity, or
		 * supplemental cart item data, before it is passed into CartController::add_to_cart and stored to session.
		 *
		 * CartController::add_to_cart only expects the keys id, quantity, variation, and cart_item_data, so other values
		 * may be ignored. CartController::add_to_cart (and core) do already have a filter hook called
		 * woocommerce_add_cart_item, but this does not have access to the original Store API request like this hook does.
		 *
		 * @since 8.8.0
		 *
		 * @param array $add_to_cart_data An array of cart item data.
		 * @return array
		 */
		$add_to_cart_data = apply_filters(
			'woocommerce_store_api_add_to_cart_data',
			array(
				'id'             =&gt; $request['id'],
				'quantity'       =&gt; $request['quantity'],
				'variation'      =&gt; $request['variation'],
				'cart_item_data' =&gt; [],
			),
			$request
		);

		$this-&gt;cart_controller-&gt;add_to_cart( $add_to_cart_data );

		$response = rest_ensure_response( $this-&gt;schema-&gt;get_item_response( $this-&gt;cart_controller-&gt;get_cart_for_response() ) );
		$response-&gt;set_status( 201 );
		return $response;
	}
}
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