Password.ex

defmodule Password do
  def generate(mac_address) do
    mac_address |> check |> do_generate
  end

  @regex_for_mac ~r/^([0-9A-Fa-f]{2}[:-]){5}([0-9A-Fa-f]{2})$/
  defp check(mac) do
    if Regex.match?(@regex_for_mac, mac) do
      {:ok, mac}
    else
      {:invalid, "Mac Address is Invalid."}
    end
  end

  defp do_generate({:invalid, message}), do: message
  defp do_generate({:ok, mac}), do:
    :sha256
    |> :crypto.hash(mac)
    |> Base.encode16
    |> String.slice(0..7)
end