formula

defmodule Formula.Actions.GetFields do
  @moduledoc """
  Return the fields given a formula
  """
  alias Formula.Function
  alias Formula.Symbol

  @spec call(String.t()) :: list(String.t())
  def call(formula) do
    case Formula.parse_formula(formula) do
      %Function{arguments: arguments} ->
        arguments
        |> Enum.map(&get_arguments/1)
        |> List.flatten()
        |> Enum.reject(&is_nil/1)
        |> Enum.uniq()

      {:error, error} ->
        {:error, error}
    end
  end

  defp get_arguments(%Decimal{}), do: nil

  defp get_arguments(%Symbol{name: name}), do: name

  defp get_arguments(%Function{arguments: arguments}),
    do: Enum.map(arguments, &get_arguments/1)
end