class TemperatureConverter
  attr_reader :input_scale, :output_scale
  
  def initialize(input_scale, output_scale)
      @input_scale = input_scale
      @output_scale = output_scale
  end
  
  def convert_temp(grades)
      converter = "#{input_scale}_to_#{output_scale}"
      if respond_to? converter, true
        send(converter, grades)
      else
          raise Exception.new "Invalid scales"
      end
  end
  
  private

  def celsius_to_kelvin(grades)
      grades + 273.15 
  end

  def celsius_to_fahrenheit(grades)
     (grades * 9.0 / 5) + 32 
  end

  def kelvin_to_celsius(grades)
      grades - 273.15
  end

  def kelvin_to_fahrenheit(grades)
      celsius = kelvin_to_celsius(grades)
      celsius_to_fahrenheit(celsius)
  end

  def fahrenheit_to_celsius(grades)
      (grades - 32) * 5.0 / 9
  end

  def fahrenheit_to_kelvin(grades)
      celsius = fahrenheit_to_celsius(grades)
      celsius_to_kelvin(celsius)
  end
end

def convert_temp(grades, input_scale:, output_scale: 'celsius')
  TemperatureConverter.new(input_scale, output_scale).convert_temp(grades)
end