beer_song.exs

defmodule BeerSong do
  @doc """
  Get a single verse of the beer song
  """
  @spec verse(integer) :: String.t()
  @on "on the wall"
  def verse(n), do:
    """
    #{String.capitalize(beers(n))} #{@on}, #{beers(n)}.
    #{action(n)}, #{beers(n - 1)} #{@on}.
    """
  defp beers(-1), do: beers(99)
  defp beers(n), do: "#{how_many(n)} bottle#{plural(n)} of beer"
  defp action(0), do: "Go to the store and buy some more"
  defp action(n), do: "Take #{pronoun(n)} down and pass it around"
  defp plural(1), do: ""
  defp plural(_), do: "s"
  defp pronoun(1), do: "it"
  defp pronoun(_), do: "one"
  defp how_many(0), do: "no more"
  defp how_many(n), do: n

  @doc """
  Get the entire beer song for a given range of numbers of bottles.
  """
  @spec lyrics(Range.t()) :: String.t()
  def lyrics(range \\ 99..0), do: Enum.map_join(range, "\n", &verse/1)
end