Game.scala

sealed trait Game {
  def handleCommand(command: GameCommand): Either[GameRulesViolation, Game]
  def applyEvent: PartialFunction[GameEvent, Game]
}

case class UninitializedGame(...) extends Game {
  def start(players: Seq[PlayerId]): Either[GameRulesViolation, Game]
}

case class RunningGame(...) extends Game {
  def roll(player: PlayerId): Either[GameRulesViolation, Game]
  def tickCountdown(): Game
}

case class FinishedGame(...) extends Game {}