case Code.ensure_loaded(Ecto.UUID) do
  {:module, _} ->
    defmodule AbsintheUtils.Scalars.UUID do
      @moduledoc """
      The UUID scalar type allows UUID compliant strings to be passed in and out.
      Requires `{ :ecto, ">= 0.0.0" }` package: https://github.com/elixir-ecto/ecto

      Based in the
      [recipes on Absinthe's wiki](https://github.com/absinthe-graphql/absinthe/wiki/Scalar-Recipes)

      **Usage:**

      Import the type in your schema `import_types(AbsintheUtils.Scalars.JSON)` and you will be able
      to use the `:json` type.
      """
      use Absinthe.Schema.Notation

      alias Ecto.UUID

      scalar :uuid, name: "UUID" do
        description("""
        The `UUID` scalar type represents UUID compliant string data, represented as UTF-8
        character sequences. The UUID type is most often used to represent unique
        machine-readable ID strings.
        """)

        serialize(&encode/1)
        parse(&decode/1)
      end

      @spec decode(Absinthe.Blueprint.Input.String.t()) :: {:ok, term()} | :error
      @spec decode(Absinthe.Blueprint.Input.Null.t()) :: {:ok, nil}
      defp decode(%Absinthe.Blueprint.Input.String{value: value}) do
        UUID.cast(value)
      end

      defp decode(%Absinthe.Blueprint.Input.Null{}) do
        {:ok, nil}
      end

      defp decode(_), do: :error

      defp encode(value) do
        case UUID.cast(value) do
          :error ->
            raise Absinthe.SerializationError,
                  "Could not serialize term #{inspect(value)} as type UUID."

          {:ok, uuid} ->
            uuid
        end
      end
    end

  _ ->
    nil
end