defmodule Anagram do
  @doc """
  Returns all candidates that are anagrams of, but not equal to, 'base'.
  """
  @spec match(String.t(), [String.t()]) :: [String.t()]
  def match(base, candidates) do
    candidates
    |> Enum.filter(&anagram?(normalize(base), normalize(&1)))
  end

  defp anagram?(base, base), do: false
  defp anagram?(base, candidate), do: hash(base) == hash(candidate)

  @spec normalize(String.t()) :: String.t()
  defp normalize(string), do: string |> String.downcase() |> String.graphemes()

  @spec hash(String.t()) :: Map.t()
  defp hash(string) do
    Enum.reduce(string, %{}, fn char, acc -> Map.update(acc, char, 1, &(&1 + 1)) end)
  end
end