herzrasen roman numerals

roman_numerals.ex

defmodule RomanNumerals do
  @romans [
    {1000, "M"},
    {900, "CM"},
    {500, "D"},
    {400, "CD"},
    {100, "C"},
    {90, "XC"},
    {50, "L"},
    {40, "XL"},
    {10, "X"},
    {9, "IX"},
    {5, "V"},
    {4, "IV"},
    {1, "I"}
  ]

  # @romans %{
    # 1 => "I",
    # 4 => "IV",
    # 5 => "V",
    # 9 => "IX",
    # 10 => "X",
    # 40 => "XL",
    # 50 => "L",
    # 90 => "XC",
    # 100 => "C",
    # 400 => "CD",
    # 500 => "D",
    # 900 => "CM",
    # 1000 => "M"
  # }

  @doc """
  Convert the number to a roman number.
  """
  @spec numeral(pos_integer) :: String.t()
  def numeral(number) do
    {0, digits} = to_roman(number, "")

    digits
    # |> to_string()
  end

  defp to_roman(0, digits), do: {0, digits}

  defp to_roman(number, digits) do
    # closest = closest_roman(number)
    {closest, numeral} =
      Enum.find(@romans, fn {value, _numeral} ->
        number >= value
      end)

    to_roman(number - closest, digits <> numeral)
  end

  # defp closest_roman(number) do
  #   Map.keys(@romans)
  #   |> Enum.filter(&smaller_or_equal?(number, &1))
  #   |> Enum.min_by(&diff_between(number, &1))
  # end

  # defp smaller_or_equal?(n, m), do: n >= m
  # defp diff_between(n, m), do: n - m
end