defmodule WordCount do
  @doc """
  Count the number of words in the sentence.

  Words are compared case-insensitively.
  """
  @spec count(String.t()) :: map
  def count(sentence) do
    sentence
    |> String.split(~r/[\s,.:!?_]+/, trim: true)
    |> Enum.reject(&String.match?(&1, ~r/[&@$%^]+/))
    |> Enum.map(&String.trim(&1, "'"))
    |> Enum.reduce(%{}, fn word, acc ->
      Map.update(acc, String.downcase(word), 1, &(&1 + 1))
    end)
  end
end