type Cents = int
type ChargeId = string

nominal OrderId = string
type Order = {
  id: OrderId,
  totalCents: int,
  status: "pending" | "paid"
}

error OrderNotFound = { id: OrderId }
error PaymentDeclined = { reason: string }

service Orders {
  find(id: OrderId): Option<Order>
  save(order: Order): void
}

service Payments {
  charge(amount: Cents): ChargeId fails PaymentDeclined
}

const findOrder = (id: OrderId) =>
  Orders.find(id) ?? fail(OrderNotFound({ id }))

const chargeOrder = (order: Order) => {
  retry(() => Payments.charge(order.totalCents), { times: 2 })
  order
}

const markPaid = (order: Order) =>
  ({ ...order, status: "paid" })

const saveOrder = (order: Order) => {
  Orders.save(order)
  order
}

export const pay = (id: OrderId): Order
  fails OrderNotFound | PaymentDeclined
  uses Orders | Payments.charge =>
  id
    |> findOrder
    |> chargeOrder
    |> markPaid
    |> saveOrder