simetric

defmodule Simetric.Jaro.Winkler do
  def compare(str1, str2) do
    case Simetric.Jaro.compare(str1, str2) do
      0.0 -> 0.0
      1.0 -> 1.0
      dist ->
        dist + (prefix(str1, str2) * 0.1 * (1 - dist))
    end
  end

  defp prefix(str1, str2) do
    prefix(str1, str2, 0, 4)
  end

  defp prefix(_str1, _str2, count, 0), do: count
  defp prefix(_str, "", count, _lim),  do: count
  defp prefix("", _str, count, _lim),  do: count

  defp prefix(str1, str2, count, lim) do
    {char, rest1} = String.next_grapheme(str1)

    case String.next_grapheme(str2) do
      {^char, rest2} ->
        prefix(rest1, rest2, count + 1, lim - 1)

      {_, _} -> count
    end
  end
end