LargeWithdrawals.kt

package org.kollektions.examples.basics

import org.kollektions.consumers.asList
import org.kollektions.consumers.consume
import org.kollektions.consumers.sumOfBigDecimal
import org.kollektions.transformations.*
import java.math.BigDecimal
import kotlin.test.Test
import kotlin.test.assertEquals

class LargeWithdrawals {
    private val expected = listOf(TransactionWithCurrentBalance(currentBalance=BigDecimal(39), amount=BigDecimal(-50)))

    private val amountsToProcess = listOf(BigDecimal(100), BigDecimal(-10), BigDecimal(-1), BigDecimal(-50))

    @Test
    fun `creates many short-lived objects v2`() {
        val currentBalance = sumOfBigDecimal()
        val largeWithdrawals = amountsToProcess.consume(
            keepState(currentBalance)
                .peek { println("Before filtering and mapping: item $it, currentBalance ${currentBalance.sum()}") }
                .mapTo { TransactionWithCurrentBalance(currentBalance.sum(), it) }
                .peek { println("After mapping, before filtering: $it") }
                .filterOn { -it.amount > it.currentBalance * BigDecimal("0.5") }
                .peek { println("After filtering: $it") }
                .asList())
        assertEquals(expected, largeWithdrawals[0])
    }

    @Test
    fun `does not create short-lived objects, maps and filters in one step v2`() {
        val currentBalance = sumOfBigDecimal()
        val amounts = listOf(BigDecimal(100), BigDecimal(-10), BigDecimal(-1), BigDecimal(-50))
        val transformation =
            { value: BigDecimal ->
                when {
                    -value > (currentBalance.sum() * BigDecimal("0.5")) -> sequenceOf(TransactionWithCurrentBalance(currentBalance.sum(), value))
                    else -> sequenceOf()
                }
            }

        val largeWithdrawals = amounts.consume(
            keepState(currentBalance)
                .peek { println("Before transformation: item $it, currentBalance ${currentBalance.sum()}") }
                .transformTo(transformation)
                .peek { println("After transformation: $it") }
                .asList())
        assertEquals(expected, largeWithdrawals[0])
    }

    data class TransactionWithCurrentBalance(val currentBalance: BigDecimal, val amount: BigDecimal)
}