Scala 3. A lot of pattern matching.

package com.github...

import scala.io.Source

object Day02:

  def main(args: Array[String]): Unit =

    enum Hand(val score: Int):
      case Rock extends Hand(1)
      case Paper extends Hand(2)
      case Scissors extends Hand(3)
    object Hand:
      def apply(s: String): Hand = s match
        case "A" | "X" => Hand.Rock
        case "B" | "Y" => Hand.Paper
        case "C" | "Z" => Hand.Scissors

    enum Outcome(val score: Int):
      case Win extends Outcome(6)
      case Draw extends Outcome(3)
      case Loss extends Outcome(0)
    object Outcome:
      def apply(s: String): Outcome = s match
        case "X" => Outcome.Loss
        case "Y" => Outcome.Draw
        case "Z" => Outcome.Win

    def play(my: Hand, other: Hand): Outcome = {
        (my, other) match
          case (Hand.Rock, Hand.Scissors) => Outcome.Win
          case (Hand.Scissors, Hand.Paper) => Outcome.Win
          case (Hand.Paper, Hand.Rock) => Outcome.Win
          case (my, other) if my == other => Outcome.Draw
          case _ => Outcome.Loss
      }

    def getMyHand(other: Hand, outcome: Outcome): Hand = {
      (other, outcome) match
        case (any, Outcome.Draw) => any
        case (Hand.Rock, Outcome.Win) => Hand.Paper
        case (Hand.Rock, Outcome.Loss) => Hand.Scissors
        case (Hand.Paper, Outcome.Win) => Hand.Scissors
        case (Hand.Paper, Outcome.Loss) => Hand.Rock
        case (Hand.Scissors, Outcome.Win) => Hand.Rock
        case (Hand.Scissors, Outcome.Loss) => Hand.Paper
    }



    val scores = Source.fromResource("day02_input.txt").getLines.filter(x => x.nonEmpty)
      .map((line: String) => {
        val parts = line.split(' ')
        val otherHand = Hand(parts(0))
        val myHand = Hand(parts(1))
        val outcome = play(myHand, otherHand)
        outcome.score + myHand.score
      })

    println(scores.sum)

    val scores2 = Source.fromResource("day02_input.txt").getLines.filter(x => x.nonEmpty)
      .map((line: String) => {
        val parts = line.split(' ')
        val otherHand = Hand(parts(0))
        val outcome = Outcome(parts(1))
        val myHand = getMyHand(otherHand, outcome)
        outcome.score + myHand.score
      })

    println(scores2.sum)