package tf.bug.aoc.y2020

import cats.effect._
import cats.syntax.all._
import fs2._
import scala.collection.SortedSet
import tf.bug.aoc.Day

object Day5 extends Day {

  override def part1[F[_]: Async]: Pipe[F, String, String] =
    (lines: Stream[F, String]) => {
      lines.through(seats[F])
        .fold1(_.max(_))
        .map(_.show)
    }

  case class SearchState(min: Int, max: Int, sum: Int)

  override def part2[F[_]: Async]: Pipe[F, String, String] =
    (lines: Stream[F, String]) => {
      lines
        .filter(_.nonEmpty)
        .through(seats[F])
        .fold(SearchState(Int.MaxValue, Int.MinValue, 0)) {
          case (SearchState(min, max, sum), seat) =>
            val newMin = seat.min(min)
            val newMax = seat.max(max)
            val newSum = sum + seat
            SearchState(newMin, newMax, newSum)
        }
        .map {
          case SearchState(min, max, sum) =>
            val range = (max - min) + 1
            val total = ((max + min) * range) / 2
            total - sum
        }
        .map(_.show)
    }

  def seats[F[_]: Async]: Pipe[F, String, Int] =
    _.map(_.foldLeft(0) {
      case (id, ch) =>
        val newBit = ((ch & 4) >>> 2) ^ 1
        (id * 2) + newBit
    })

}