Order Processing - Orchestration

order_service.kt

class OrderService(
    inventoryService: InventoryService,
    paymentService: PaymentService,
    shipmentService: ShipmentService,
    emailService: EmailService) {
    fun processOrder(order: Order): Status {
        val customerEmail = customerService.getEmailAddress(order.customerId)

        val checkItemAvailability = {
            if (order.items.all { inventoryService.isAvailable(it) }) SUBMITTED else ITEMS_UNAVAILABLE
        }

        val processPayment = {
            val total = order.items.sumOf { catalogService.getPrice(it) }
            val accountNumber = customerService.getAccountNumber(order.customerId)
            if (paymentService.processPayment(total, accountNumber)) PAID else PAYMENT_FAILED
        }

        val sendShipment = {
            shipmentService.shipOrder(order)
            order.items.forEach { inventoryService.decreaseInventory(it) }
            SHIPPED
        }

        return sequenceOf(
            checkItemAvailability,
            processPayment,
            sendShipment
        )
            .map { it() }
            .onEach { emailService.notify(customerEmail, it) }
            .firstOrNull { !it.isOk() } ?: SHIPPED
    }
}