FSM-sample.kt

// BacsPayment
/*

    ----,
    SQS  ) => Received => AccountCheck => MandateCheck => Withdraw => Succeeded
    ----'

 */
 
fun processPayment(payment: BacsPayment<Received>) {
    try {
        val acccountCheck: BacsPayment<AccountChecked> = accountCheck(payment)
        val mandateCheck: BacsPayment<MandateChecked> =  mandateCheck(acccountChecked)
        val debit: BacsPayment<DebitAttempted> = debit(currencyCheck)
        completeProcessing(debit)
    } catch(e: BacsPaymentException) {
        
    }
}
fun accountCheck(payment: BacsPayment<Received>): BacsPayment<AccountChecked> = TODO()

fun mandateCheck(payment: BacsPayment<AccountCheckPassed>): BacsPayment<MandateChecked> = TODO()

fun debit(payment: BacsPayment<CurrencyCheckPassed>): BacsPayment<DebitAttempted> = TODO()

fun completeProcessing(payment: BacsPayment<DebitSuccessful>): BacsPayment<Succeeded> = TODO()