$product->is_sold_individually() ) {
			$request['quantity'] = apply_filters( 'woocommerce_add_to_cart_sold_individually_quantity', 1, $request['quantity'], $product_id, $variation_id, $request['cart_item_data'] );
		}

		return $request;
	}

	/**
	 * If variations are set, validate and format the values ready to add to the cart.
	 *
	 * @throws RouteException Exception if invalid data is detected.
	 *
	 * @param array $request Add to cart request params.
	 * @return array Updated request array.
	 */
	protected function parse_variation_data( $request ) {
		$product = $this->get_product_for_cart( $request );

		// Remove variation request if not needed.
		if ( ! $product->is_type( array( 'variation', 'variable' ) ) ) {
			$request['variation'] = [];
			return $request;
		}

		// Flatten data and format posted values.
		$variable_product_attributes = $this->get_variable_product_attributes( $product );
		$request['variation']        = $this->sanitize_variation_data( wp_list_pluck( $request['variation'], 'value', 'attribute' ), $variable_product_attributes );

		// If we have a parent product, find the variation ID.
		if ( $product->is_type( 'variable' ) ) {
			$request['id'] = $this->get_variation_id_from_variation_data( $request, $product );
		}

		// Now we have a variation ID, get the valid set of attributes for this variation. They will have an attribute_ prefix since they are from meta.
		$expected_attributes = wc_get_product_variation_attributes( $request['id'] );
		$missing_attributes  = [];

		foreach ( $variable_product_attributes as $attribute ) {
			if ( ! $attribute['is_variation'] ) {
				continue;
			}

			$prefixed_attribute_name = 'attribute_' . sanitize_title( $attribute['name'] );
			$expected_value          = isset( $expected_attributes[ $prefixed_attribute_name ] ) ? $expected_attributes[ $prefixed_attribute_name ] : '';
			$attribute_label         = wc_attribute_label( $attribute['name'] );

			if ( isset( $request['variation'][ wc_variation_attribute_name( $attribute['name'] ) ] ) ) {
				$given_value = $request['variation'][ wc_variation_attribute_name( $attribute['name'] ) ];

				if ( $expected_value === $given_value ) {
					continue;
				}

				// If valid values are empty, this is an 'any' variation so get all possible values.
				if ( '' === $expected_value && in_array( $given_value, $attribute->get_slugs(), true ) ) {
					continue;
				}

				throw new RouteException(
					'woocommerce_rest_invalid_variation_data',
					/* translators: %1$s: Attribute name, %2$s: Allowed values. */
					sprintf( __( 'Invalid value posted for %1$s. Allowed values: %2$s', 'woocommerce' ), $attribute_label, implode( ', ', $attribute->get_slugs() ) ),
					400
				);
			}

			// If no attribute was posted, only error if the variation has an 'any' attribute which requires a value.
			if ( '' === $expected_value ) {
				$missing_attributes[] = $attribute_label;
			}
		}

		if ( ! empty( $missing_attributes ) ) {
			throw new RouteException(
				'woocommerce_rest_missing_variation_data',
				/* translators: %s: Attribute name. */
				__( 'Missing variation data for variable product.', 'woocommerce' ) . ' ' . sprintf( _n( '%s is a required field', '%s are required fields', count( $missing_attributes ), 'woocommerce' ), wc_format_list_of_items( $missing_attributes ) ),
				400
			);
		}

		return $request;
	}

	/**
	 * Try to match request data to a variation ID and return the ID.
	 *
	 * @throws RouteException Exception if variation cannot be found.
	 *
	 * @param array       $request Add to cart request params.
	 * @param \WC_Product $product Product being added to the cart.
	 * @return int Matching variation ID.
	 */
	protected function get_variation_id_from_variation_data( $request, $product ) {
		$data_store       = \WC_Data_Store::load( 'product' );
		$match_attributes = $request['variation'];
		$variation_id     = $data_store->find_matching_product_variation( $product, $match_attributes );

		if ( empty( $variation_id ) ) {
			throw new RouteException(
				'woocommerce_rest_variation_id_from_variation_data',
				__( 'No matching variation found.', 'woocommerce' ),
				400
			);
		}

		return $variation_id;
	}

	/**
	 * Format and sanitize variation data posted to the API.
	 *
	 * Labels are converted to names (e.g. Size to pa_size), and values are cleaned.
	 *
	 * @throws RouteException Exception if variation cannot be found.
	 *
	 * @param array $variation_data Key value pairs of attributes and values.
	 * @param array $variable_product_attributes Product attributes we're expecting.
	 * @return array
	 */
	protected function sanitize_variation_data( $variation_data, $variable_product_attributes ) {
		$return = [];

		foreach ( $variable_product_attributes as $attribute ) {
			if ( ! $attribute['is_variation'] ) {
				continue;
			}
			$attribute_label          = wc_attribute_label( $attribute['name'] );
			$variation_attribute_name = wc_variation_attribute_name( $attribute['name'] );

			// Attribute labels e.g. Size.
			if ( isset( $variation_data[ $attribute_label ] ) ) {
				$return[ $variation_attribute_name ] =
					$attribute['is_taxonomy']
						?
						sanitize_title( $variation_data[ $attribute_label ] )
						:
						html_entity_decode(
							wc_clean( $variation_data[ $attribute_label ] ),
							ENT_QUOTES,
							get_bloginfo( 'charset' )
						);
				continue;
			}

			// Attribute slugs e.g. pa_size.
			if ( isset( $variation_data[ $attribute['name'] ] ) ) {
				$return[ $variation_attribute_name ] =
					$attribute['is_taxonomy']
						?
						sanitize_title( $variation_data[ $attribute['name'] ] )
						:
						html_entity_decode(
							wc_clean( $variation_data[ $attribute['name'] ] ),
							ENT_QUOTES,
							get_bloginfo( 'charset' )
						);
			}
		}
		return $return;
	}

	/**
	 * Get product attributes from the variable product (which may be the parent if the product object is a variation).
	 *
	 * @throws RouteException Exception if product is invalid.
	 *
	 * @param \WC_Product $product Product being added to the cart.
	 * @return array
	 */
	protected function get_variable_product_attributes( $product ) {
		if ( $product->is_type( 'variation' ) ) {
			$product = wc_get_product( $product->get_parent_id() );
		}

		if ( ! $product || 'trash' === $product->get_status() ) {
			throw new RouteException(
				'woocommerce_rest_cart_invalid_parent_product',
				__( 'This product cannot be added to the cart.', 'woocommerce' ),
				400
			);
		}

		return $product->get_attributes();
	}
}