defmodule Ash.Resource.Change.SetAttribute do
  @moduledoc false
  use Ash.Resource.Change
  alias Ash.Changeset

  def init(opts) do
    with :ok <- validate_attribute(opts[:attribute]),
         :ok <- validate_value(opts[:value]) do
      {:ok, opts}
    end
  end

  defp validate_attribute(nil), do: {:error, "attribute is required"}
  defp validate_attribute(value) when is_atom(value), do: :ok
  defp validate_attribute(other), do: {:error, "attribute is invalid: #{inspect(other)}"}
  defp validate_value(value) when is_function(value, 0), do: :ok

  defp validate_value(value) when is_function(value),
    do: {:error, "only 0 argument functions are supported"}

  defp validate_value(_), do: :ok

  def change(changeset, opts, _) do
    value =
      case opts[:value] do
        value when is_function(value) -> value.()
        value -> value
      end

    Changeset.force_change_attribute(changeset, opts[:attribute], value)
  end
end