package rps

import kotlin.random.Random

fun main() {
  println(playGame(100))
}

/**
 * A possible move in a game of rock-paper-scissors.
 *
 * [strongAgainst] is a function for lazy evaluation because otherwise we can’t access SCISSORS before it’s been defined.
 * If the game needs to be expanded (e.g. the somewhat common “rock, paper, scissors, salamander, spock”),
 * this argument could be a List<Move> instead.
 */
enum class Move(val strongAgainst: () -> Move) {
  ROCK({ SCISSORS }),
  PAPER({ ROCK }),
  SCISSORS({ PAPER })
}

// purposely not calling this Result to avoid confusion with kotlin.Result and similar
enum class Outcome {
  WIN,
  DRAW,
  LOSS
}

// Named Triple for readability
data class GameSummary(val wins: Int, val draws: Int, val losses: Int)

/** Determine the [Outcome] of [first] vs [second] from the perspective of [first]. */
fun determineOutcome(first: Move, second: Move): Outcome = when {
  first.strongAgainst() == second -> Outcome.WIN
  first == second -> Outcome.DRAW
  else -> Outcome.LOSS
}

// Note: This would be slightly more efficient (but a lot less elegant) with an imperative loop and three mutable integers.
fun List<Outcome>.calculateGameSummary() = GameSummary(
  wins = count { it == Outcome.WIN },
  draws = count { it == Outcome.DRAW },
  losses = count { it == Outcome.LOSS },
)

fun playGame(turns: Int): GameSummary = generateSequence { randomMove() }
  .take(turns)
  .map { determineOutcome(it, Move.ROCK) }
  .toList()
  .calculateGameSummary()

fun randomMove(): Move = Move.values().let { allMoves ->
  allMoves[Random.nextInt(allMoves.size)]
}