Complement for Distance.kt

DistanceUnit.kt

import kotlin.math.abs
import kotlin.math.roundToLong

enum class DistanceUnit(private val orderLowerIsLarger: Int) {
    KILOMETERS(1),
    HECTOMETERS(2),
    DECAMETERS(3),
    METERS(4),
    DECIMETERS(5),
    CENTIMETERS(6),
    MILLIMETERS(7);

    fun convert(value: Double, other: DistanceUnit): Long {
        val firstIndex = largestFirst.indexOf(this)
        val lastIndex = largestFirst.indexOf(other)

        val (numberOfZeros, inversion) = if (firstIndex > lastIndex) {
            firstIndex - lastIndex to -1
        } else {
            lastIndex - firstIndex to 1
        }
        val factor = (0 until numberOfZeros).fold("1") { acc, _ ->
            acc + "0"
        }.toLong() * inversion

        return (if (factor < 0) {
             abs(value / factor)
        } else {
            value * factor
        }.roundToLong()
)    }

    companion object {
        val largestFirst = values().sortedBy { it.orderLowerIsLarger }
    }
}