public function maybe_add_meta( $data, $resource ) {

		if ( isset( $this->server->params['GET']['filter']['meta'] ) && 'true' === $this->server->params['GET']['filter']['meta'] && is_object( $resource ) ) {

			// don't attempt to add meta more than once
			if ( preg_grep( '/[a-z]+_meta/', array_keys( $data ) ) ) {
				return $data;
			}

			// define the top-level property name for the meta
			switch ( get_class( $resource ) ) {

				case 'WC_Order':
					$meta_name = 'order_meta';
					break;

				case 'WC_Coupon':
					$meta_name = 'coupon_meta';
					break;

				case 'WP_User':
					$meta_name = 'customer_meta';
					break;

				default:
					$meta_name = 'product_meta';
					break;
			}

			if ( is_a( $resource, 'WP_User' ) ) {

				// customer meta
				$meta = (array) get_user_meta( $resource->ID );

			} else {

				// coupon/order/product meta
				$meta = (array) get_post_meta( $resource->get_id() );
			}

			foreach ( $meta as $meta_key => $meta_value ) {

				// don't add hidden meta by default
				if ( ! is_protected_meta( $meta_key ) ) {
					$data[ $meta_name ][ $meta_key ] = maybe_unserialize( $meta_value[0] );
				}
			}
		}

		return $data;
	}