exercism/elixir/crypto-square/lib/crypto_square.ex

defmodule CryptoSquare do
  @doc """
  Encode string square methods
  ## Examples

    iex> CryptoSquare.encode("abcd")
    "ac bd"
  """
  @spec encode(String.t()) :: String.t()
  def encode(str) do
    str
    |> normalize()
    |> square()
  end

  defp normalize(str) do
    str
    |> String.downcase()
    |> String.replace(~r/[^a-z0-9]/, "")
  end

  defp square(""), do: ""

  defp square(str) do
    length = String.length(str)
    row = round(ceil(length ** 0.5))

    str
    |> String.split("", trim: true)
    |> Enum.chunk_every(row, row, List.duplicate(" ", row))
    |> Enum.zip()
    |> Enum.map(&Tuple.to_list(&1))
    |> Enum.map_join(" ", &Enum.join(&1))
  end
end