じゃんけん

rock_paper_scissors.groovy

package tddbc

import groovy.transform.Canonical

enum Hand {
    ROCK,
    PAPER,
    SCISSORS
}

@Canonical
class Player {
    Hand hand
    Result result
}

enum Result {
    WIN,
    ROSE,
    EVEN
}

@Canonical
class Game {

    Player defender
    Player challenger

    Player getWinner() {
        if (this.defender.result.is(Result.WIN)) return this.defender
        if (this.defender.result.is(Result.EVEN)) return this.defender
        this.challenger
    }

}

class Observer {

    def notify = { Game game ->
        game.defender.result = judge(game.defender.hand, game.challenger.hand)

        switch (game.defender.result) {
            case Result.WIN:
                game.challenger.result = Result.ROSE
                break
            case Result.ROSE:
                game.challenger.result = Result.WIN
                break
            default:
                game.challenger.result = Result.EVEN
                break
        }
        game
    }

    def judge = { Hand defender, Hand challenger ->
        switch (defender) {
            case Hand.ROCK:
                if (challenger.is(Hand.SCISSORS)) return Result.WIN
                if (challenger.is(Hand.PAPER)) return Result.ROSE
                return Result.EVEN
            case Hand.PAPER:
                if (challenger.is(Hand.ROCK)) return Result.WIN
                if (challenger.is(Hand.SCISSORS)) return Result.ROSE
                return Result.EVEN
            case Hand.SCISSORS:
                if (challenger.is(Hand.PAPER)) return Result.WIN
                if (challenger.is(Hand.ROCK)) return Result.ROSE
                return Result.EVEN
        }
    }

}

def challenger = new Player(hand: Hand.ROCK)
def defender = new Player(hand: Hand.PAPER)
def game = new Game(challenger: challenger, defender: defender)

def result = new Observer().notify game

assert result.winner == defender