package aoc
package day08

import scala.annotation.tailrec

val dayNumber = "08"

@main def part1: Unit =
  println(part1(loadInput(dayNumber)))

@main def part2: Unit =
  println(part2(loadInput(dayNumber)))

def findPathLength(
    nodeMap: Map[String, (String, String)],
    instructions: String,
    startNode: String,
    endNode: String => Boolean
): Long =
  LazyList
    .continually(instructions)
    .flatMap(_.toSeq)
    .scanLeft(startNode) {
      case (node, 'L') => nodeMap(node)._1
      case (node, 'R') => nodeMap(node)._2
    }
    .takeWhile(!endNode(_))
    .length

def part1(input: String) =
  val Array(instructions, nodesStr) = input.split("\n\n")
  val nodeMap = nodesStr
    .split('\n')
    .map { case s"$name = ($left, $right)" => (name, (left, right)) }
    .toMap
  findPathLength(nodeMap, instructions, "AAA", _ == "ZZZ").toString

def part2(input: String) =
  val Array(instructions, nodesStr) = input.split("\n\n")
  val nodeMap = nodesStr
    .split('\n')
    .map { case s"$name = ($left, $right)" => (name, (left, right)) }
    .toMap

  @tailrec def gcd(a: Long, b: Long): Long =
    if (b == 0) a.abs else gcd(b, a % b)
  def lcm(a: Long, b: Long) =
    (a * b).abs / gcd(a, b)

  nodeMap.keySet
    .filter(_.endsWith("A"))
    .map(node => findPathLength(nodeMap, instructions, node, _.endsWith("Z")))
    .reduce(lcm)
    .toString