package snake

/** m05 game: one `update` turns every action into a new state; replaying a game is a fold over its actions. */
object Game:

  def update(state: GameState, action: Action): GameState = action match
    case Action.Tick       => Spawn.tick(state)
    case Action.Turn(dir)  => Rules.turn(state, dir)
    case _                 => state // TogglePause, Restart and Frame arrive in m10

  def replay(state: GameState, actions: List[Action]): GameState = actions.foldLeft(state)(update)

  // scanLeft is foldLeft that keeps every intermediate result.
  def history(state: GameState, actions: List[Action]): List[GameState] = actions.scanLeft(state)(update)