fun main() {

    data class Point(val x: Int, val y: Int, val z: Int)

    fun List<String>.parse(): Set<Point> {
        val pointRegex = "(\\d+),(\\d+),(\\d+)".toRegex()
        return this
            .mapNotNull { line -> pointRegex.matchEntire(line)?.groupValues }
            .map { gv -> Point(gv[1].toInt(), gv[2].toInt(), gv[3].toInt()) }
            .toSet()
    }

    fun Point.getAdjacent() = listOf(
        copy(x = x - 1),
        copy(x = x + 1),
        copy(y = y - 1),
        copy(y = y + 1),
        copy(z = z - 1),
        copy(z = z + 1),
    )

    fun getSurrounding(points: Set<Point>): Set<Point> {
        val xRange = (points.minOf { it.x } - 1 .. points.maxOf { it.x } + 1)
        val yRange = (points.minOf { it.y } - 1 .. points.maxOf { it.y } + 1)
        val zRange = (points.minOf { it.z } - 1 .. points.maxOf { it.z } + 1)

        tailrec fun expand(surrounding: Set<Point>): Set<Point> {
            val newSurrounding = surrounding
                .flatMap { it.getAdjacent() + it }
                .filter { it.x in xRange && it.y in yRange && it.z in zRange && it !in points }
                .toSet()
            return if (surrounding.size == newSurrounding.size) {
                surrounding
            } else {
                expand(newSurrounding)
            }
        }

        val initialSurrounding = run {
            val boundaries = listOf(
                xRange.flatMap { x -> yRange.map { y -> Point(x, y, zRange.first) } },
                xRange.flatMap { x -> yRange.map { y -> Point(x, y, zRange.last) } },
                xRange.flatMap { x -> zRange.map { z -> Point(x, yRange.first, z) } },
                xRange.flatMap { x -> zRange.map { z -> Point(x, yRange.last, z) } },
                yRange.flatMap { y -> zRange.map { z -> Point(zRange.first, y, z) } },
                yRange.flatMap { y -> zRange.map { z -> Point(zRange.last, y, z) } },
            )
            boundaries.flatten().toSet()
        }

        return expand(initialSurrounding)
    }

    fun part1(input: List<String>): Int {
        val points = input.parse()
        return points
            .flatMap { p -> p.getAdjacent().map { p2 -> (p to p2) } }
            .count { (_, p2) -> p2 !in points }
    }

    fun part2(input: List<String>): Int {
        val points = input.parse()
        val surrounding = getSurrounding(points)
        return points
            .flatMap { p -> p.getAdjacent().map { p2 -> (p to p2) } }
            .count { (_, p2) -> p2 in surrounding }
    }


    val input = readInput("day18_input")
    println("Part 1: ${part1(input)}")
    println("Part 2: ${part2(input)}")
}

