serene

defmodule Serene do
  @moduledoc """
  Serene
  """

  @annotations [:create, :read, :update, :delete]

  defmacro __using__(_) do
    quote do
      import unquote(__MODULE__)

      @before_compile unquote(__MODULE__)
      @on_definition unquote(__MODULE__)

      Module.register_attribute(__MODULE__, :actions, accumulate: true)
    end
  end

  defmacro __before_compile__(_) do
    quote do
      def __actions__, do: @actions
    end
  end

  def __on_definition__(%Macro.Env{module: module}, :def, fun, args, _, _) do
    case find_annotation(module, @annotations) do
      {action, resource} ->
        Module.put_attribute(
          module,
          :actions,
          {action, resource, {module, fun, clean_args(args)}}
        )

      _ ->
        nil
    end
  end

  def __on_definition__(_, _, _, _, _, _), do: nil

  defp find_annotation(_, []), do: nil

  defp find_annotation(module, [annotation | rest]) do
    if value = Module.get_attribute(module, annotation) do
      Module.delete_attribute(module, annotation)

      {annotation, value}
    else
      find_annotation(module, rest)
    end
  end

  defp clean_args(args) do
    Enum.map(args, fn {name, _meta, _default} -> name end)
  end
end