class Character

  # Usage: character.withdraw_resources(gold: 20, wood: 90)

  def withdraw_resources(resources)

    resources.each do |type, amount|

      current_amount = self.read_attribute("#{type}_amount")

      new_amount     = current_amount - amount



      if new_amount < 0

        raise NotEnoughResource, "Character has #{current_amount} of #{type} and can not be debited of #{amount}."

      else

        self.write_attribute("#{type}_amount", new_amount)

      end

    end



    self.save

  end





  # Define a custom exception.

  class NotEnoughResource < StandardError; end

end