states = [:stop, :drive]
transitions = %{
  stop: %{
    gas: &gas_action/1
  },
  drive: %{
    brake: &stop_action/1
  }
}

defmodule FSM do
  use GenServer

  defstruct [
    :states,
    :transitions
  ]

  def init(struct) do
    {:ok, {Enum.at(struct.states, 0), struct}}
  end

  def handle_info({:transition, transition}, {current_state, struct}) do
    case Map.get(struct.transitions, current_state) do
      nil -> {:noreply, {current_state, struct}}
      transition_map -> case Map.get(transition_map, transition) do
        nil -> {:noreply, {current_state, struct}}
        {action_name, next_state} ->
          ActionPerformer.perform_action(action_name)
          {:noreply, {next_state, struct}}
      end
    end
  end
end



#######
states = [:stop, :drive]
transitions = %{
  stop: %{
    gas: {"gas_action", :drive}
  },
  drive: %{
    brake: {"stop_action", :stop}
  }
}