defmodule KitchenCalculator do
  def get_volume(volume_pair) do
    elem(volume_pair, 1)
  end

  def to_milliliter(volume_pair) do
    volume = get_volume(volume_pair)
    case elem(volume_pair, 0) do
        :milliliter -> volume
        :fluid_ounce -> 30 * volume
        :cup -> 240 * volume
        :teaspoon -> 5 * volume
        :tablespoon -> 15 * volume
        _ -> -1
    end
  end

  def from_milliliter({:milliliter, volume}, unit) do
    case unit do
        :cup -> volume / 240
        :fluid_ounce -> volume / 30
        :teaspoon -> volume / 5
        :tablespoon -> volume / 15
        _ -> volume
    end 
  end

  def convert({unit1, volume}, unit2) do
    from_milliliter({:milliliter, to_milliliter({unit1, volume})}, unit2)
  end
end