class Day13(input: List<String>) {

    data class Layer(val depth: Int, val range: Int) {
        fun caughtAt(time: Int): Boolean =
            (time + depth) % ((range - 1) * 2) == 0
    }

    private val layers = parseInput(input)

    fun solvePart1(): Int =
        layers
            .filter { it.caughtAt(0) }
            .sumBy { it.depth * it.range }


    fun solvePart2(): Int =
        generateSequence(0, Int::inc)
            .filter { time ->
                layers.none { it.caughtAt(time) }
            }
            .first()

    private fun parseInput(input: List<String>): List<Layer> =
        input
            .map { it.split(": ") }
            .map { Layer(it[0].toInt(), it[1].toInt()) }

}