Fish Farm - Advent Of Code - Classes for task 1

fishFarm.kt

const val DAYS = 80
const val MORE_DAYS = 256
const val NEWBORN_MAX_SEED = 8
const val MAX_SEED = 6

class Fish(private var seed: Int = NEWBORN_MAX_SEED) {
    fun plusDay(): Fish? {
        if (seed == 0) {
            seed = MAX_SEED
            return Fish()
        }
        seed--
        return null
    }
}

class FishFarm(input: String) {
    private val fish = mutableListOf<Fish>()

    init {
        fish.addAll(input.split(",")
            .filter { it.trim().isNotEmpty() }
            .map { Fish(it.trim().toInt()) }
        )
    }

    private fun plusDay() {
        val newborns = fish.mapNotNull { it.plusDay() }
        fish.addAll(newborns)
    }

    fun plusDays(days: Int): Int {
        for (i in 0 until days) {
            plusDay()
        }
        return fish.size
    }
}