invoice.scala

sealed trait InvoiceStatus

case class NoGenerated() extends InvoiceStatus
case class Generated() extends InvoiceStatus
case class Paid() extends InvoiceStatus

case class Invoice[State <: InvoiceStatus](id: Option[Long], value: Long, status: State)

trait InvoiceServices {

  val generate: Invoice[NoGenerated] => Try[Invoice[Generated]] = {
    c =>
      Try {
        c.copy(status = Generated())
      }
  }

  val pay: Invoice[Generated] => Try[Invoice[Paid]] = {
    c =>
      Try {
        c.copy(status = Paid())
      }
  }
}

object InvoiceServices extends InvoiceServices