defmodule KitchenCalculator do
  defp milliliter(:milliliter), do: 1
  defp milliliter(:cup), do: 240
  defp milliliter(:fluid_ounce), do: 30
  defp milliliter(:teaspoon), do: 5
  defp milliliter(:tablespoon), do: 15

  def get_volume(_volume_pair = {_, volume}), do: volume

  def to_milliliter(_volume_pair = {from_unit, volume}),
    do:
      {:milliliter, milliliter(from_unit) * volume}

  def from_milliliter(_volume_pair = {:milliliter, volume}, to_unit),
    do:
      {to_unit, volume / milliliter(to_unit)}

  def convert(volume_pair, unit) do
    volume_pair
    |> to_milliliter
    |> from_milliliter(unit)
  end
end