onCommand

    suspend fun onCommand(
        command: CommandMessage<CreateOrder>,
        @Name("createOrderSpec") specification: CreateOrderSpec,
        commandResultAccessor: CommandResultAccessor
    ): OrderCreated {
        val createOrder = command.body
        require(createOrder.items.isNotEmpty()) {
            "items can not be empty."
        }
        createOrder.items.asFlow().collect {
            specification.require(it).awaitSingle()
        }
        val orderCreated = OrderCreated(
            orderId = command.aggregateId.id,
            items = createOrder.items.map {
                OrderItem(
                    id = GlobalIdGenerator.generateAsString(),
                    productId = it.productId,
                    price = it.price,
                    quantity = it.quantity,
                )
            },
            address = createOrder.address,
            fromCart = createOrder.fromCart,
        )
        commandResultAccessor.setCommandResult(
            OrderState::totalAmount.name,
            orderCreated.items.sumOf { it.totalPrice }
        )
        return orderCreated
    }