InvasionController.scala

  def finishInvasionBattle(
    state: State,
    invasion: FinishInvasionBattle,
    userId: String
  ) : (State, List[TrackingMessage]) = {

    validate(state, invasion.userId)
    val (afterBattle, calls) = battleEffects(state, userId)(invasion)
    (resetTarget(afterBattle)(invasion), calls)
  }