protected function set_line_item( $order, $item, $action ) {
		$creating  = ( 'create' === $action );

		// product is always required
		if ( ! isset( $item['product_id'] ) && ! isset( $item['sku'] ) ) {
			throw new WC_API_Exception( 'woocommerce_api_invalid_product_id', __( 'Product ID or SKU is required', 'woocommerce' ), 400 );
		}

		// when updating, ensure product ID provided matches
		if ( 'update' === $action ) {

			$item_product_id   = wc_get_order_item_meta( $item['id'], '_product_id' );
			$item_variation_id = wc_get_order_item_meta( $item['id'], '_variation_id' );

			if ( $item['product_id'] != $item_product_id && $item['product_id'] != $item_variation_id ) {
				throw new WC_API_Exception( 'woocommerce_api_invalid_product_id', __( 'Product ID provided does not match this line item', 'woocommerce' ), 400 );
			}
		}

		if ( isset( $item['product_id'] ) ) {
			$product_id = $item['product_id'];
		} elseif ( isset( $item['sku'] ) ) {
			$product_id = wc_get_product_id_by_sku( $item['sku'] );
		}

		// variations must each have a key & value
		$variation_id = 0;
		if ( isset( $item['variations'] ) && is_array( $item['variations'] ) ) {
			foreach ( $item['variations'] as $key => $value ) {
				if ( ! $key || ! $value ) {
					throw new WC_API_Exception( 'woocommerce_api_invalid_product_variation', __( 'The product variation is invalid', 'woocommerce' ), 400 );
				}
			}
			$variation_id = $this->get_variation_id( wc_get_product( $product_id ), $item['variations'] );
		}

		$product = wc_get_product( $variation_id ? $variation_id : $product_id );

		// must be a valid WC_Product
		if ( ! is_object( $product ) ) {
			throw new WC_API_Exception( 'woocommerce_api_invalid_product', __( 'Product is invalid.', 'woocommerce' ), 400 );
		}

		// quantity must be positive float
		if ( isset( $item['quantity'] ) && floatval( $item['quantity'] ) <= 0 ) {
			throw new WC_API_Exception( 'woocommerce_api_invalid_product_quantity', __( 'Product quantity must be a positive float.', 'woocommerce' ), 400 );
		}

		// quantity is required when creating
		if ( $creating && ! isset( $item['quantity'] ) ) {
			throw new WC_API_Exception( 'woocommerce_api_invalid_product_quantity', __( 'Product quantity is required.', 'woocommerce' ), 400 );
		}

		if ( $creating ) {
			$line_item = new WC_Order_Item_Product();
		} else {
			$line_item = new WC_Order_Item_Product( $item['id'] );
		}

		$line_item->set_product( $product );
		$line_item->set_order_id( $order->get_id() );

		if ( isset( $item['quantity'] ) ) {
			$line_item->set_quantity( $item['quantity'] );
		}
		if ( isset( $item['total'] ) ) {
			$line_item->set_total( floatval( $item['total'] ) );
		} elseif ( $creating ) {
			$total = wc_get_price_excluding_tax( $product, array( 'qty' => $line_item->get_quantity() ) );
			$line_item->set_total( $total );
			$line_item->set_subtotal( $total );
		}
		if ( isset( $item['total_tax'] ) ) {
			$line_item->set_total_tax( floatval( $item['total_tax'] ) );
		}
		if ( isset( $item['subtotal'] ) ) {
			$line_item->set_subtotal( floatval( $item['subtotal'] ) );
		}
		if ( isset( $item['subtotal_tax'] ) ) {
			$line_item->set_subtotal_tax( floatval( $item['subtotal_tax'] ) );
		}
		if ( $variation_id ) {
			$line_item->set_variation_id( $variation_id );
			$line_item->set_variation( $item['variations'] );
		}

		// Save or add to order.
		if ( $creating ) {
			$order->add_item( $line_item );
		} else {
			$item_id = $line_item->save();

			if ( ! $item_id ) {
				throw new WC_API_Exception( 'woocommerce_cannot_create_line_item', __( 'Cannot create line item, try again.', 'woocommerce' ), 500 );
			}
		}
	}