defmodule Ash.Resource.Transformers.SetPrimaryActions do
  @moduledoc """
  Creates/validates the primary action configuration

  If only one action of a given type is defined, it is marked
  as primary. If multiple exist, and one is not primary,
  this results in an error.
  """
  use Ash.Dsl.Transformer

  alias Ash.Dsl.Transformer
  alias Ash.Error.Dsl.DslError

  def transform(_resource, dsl_state) do
    dsl_state
    |> Transformer.get_entities([:actions])
    |> Enum.group_by(& &1.type)
    |> Enum.reduce_while({:ok, dsl_state}, fn
      {type, [action]}, {:ok, dsl_state} ->
        {:cont,
         {:ok,
          Transformer.replace_entity(
            dsl_state,
            [:actions],
            %{action | primary?: true},
            fn replacing_action ->
              replacing_action.name == action.name && replacing_action.type == type
            end
          )}}

      {type, actions}, {:ok, dsl_state} ->
        case Enum.count(actions, & &1.primary?) do
          0 ->
            {:halt,
             {:error,
              DslError.exception(
                message:
                  "Multiple actions of type create defined, one must be designated as `primary?: true`",
                path: [:actions, type]
              )}}

          1 ->
            {:cont, {:ok, dsl_state}}

          2 ->
            {:halt,
             {:error,
              DslError.exception(
                message:
                  "Multiple actions of type #{type} configured as `primary?: true`, but only one action per type can be the primary",
                path: [:actions, type]
              )}}
        end
    end)
  end
end