Small util to transform Map keys into atoms or strings

map_utils.ex

defmodule MyApp.MapUtils do
  @doc ~S"""
  Transform keys in a Map to atoms

  ## Examples

      iex> MyApp.Maputils.map_keys_to_atoms(%{"foo" => 1, "bar" => %{foo2: "2"}})
      {bar: %{foo2: "2"}, foo: 1}
  """
  def map_keys_to_atoms(map) when is_map(map) do
    for {key, val} <- map, into: %{} do
      {atomise(key), traverse(val, :atm)}
    end
  end

  @doc ~S"""
  Transform keys in a Map to strings

  ## Examples

      iex> MyApp.Maputils.map_keys_to_strings(%{foo: 1, bar: %{"foo2" => "2"}})
      {"bar": %{"foo2": "2"}, "foo": 1}
  """
  def map_keys_to_strings(map) when is_map(map) do
    for {key, val} <- map, into: %{} do
      {stringfy(key), traverse(val, :str)}
    end
  end

  # Make sure we know what output we want
  defp traverse(item, :str) when is_map(item), do: map_keys_to_strings(item)
  defp traverse(item, :atm) when is_map(item), do: map_keys_to_atoms(item)
  defp traverse(item) when is_map(item), do: map_keys_to_strings(item)
  defp traverse(item, _), do: item

  defp stringfy(item) do
    cond do
      is_atom(item) -> Atom.to_string(item)
      true -> item
    end
  end

  defp atomise(item) do
    cond do
      is_bitstring(item) -> String.to_atom(item)
      true -> item
    end
  end
end