package aoc.day6

import aoc._

case class Race(time: Long, distance: Long):
  def waysToWin =
    val minTime = search(0, (time - 1) / 2)
    val midOk = if time % 2 == 0 && withHold(time / 2) > distance then 1L else 0
    2 * (minTime to (time - 1) / 2).length + midOk
  @scala.annotation.tailrec
  private final def search(min: Long, max: Long): Long =
    if min >= max then min
    else
      val mid = (max + min) / 2
      if withHold(mid) <= distance then search(mid + 1, max)
      else search(min, mid)
  def withHold(k: Long) = k * (time - k)

object Parser extends CommonParser:
  val nums = rep1(num)
  def time[T](nums: Parser[T]) = "Time:" ~> nums
  def distance[T](nums: Parser[T]) = "Distance:" ~> nums

  val bigNum = rep1("""\d+""".r) ^^ (_.mkString.toLong)

  def races(ss: Seq[String]) = ss match {
    case Seq(t, d) =>
      parse(time(nums), t).get.zip(parse(distance(nums), d).get).map(Race(_, _))
  }

  def bigRace(ss: Seq[String]) = ss match {
    case Seq(t, d) =>
      Race(parse(time(bigNum), t).get, parse(distance(bigNum), d).get)
  }

def part1 =
  val races = Parser.races(lines.toSeq)
  val res = races.map(_.waysToWin).product
  println(res)

def part2 =
  val race = Parser.bigRace(lines.toSeq)
  val res = race.waysToWin
  println(res)

@main def Day6(part: Int) = part match
  case 1 => part1
  case 2 => part2