defmodule Ash.Flow.Verifiers.ValidateUniqueNames do
  @moduledoc "Validates that steps have unique names."
  use Spark.Dsl.Verifier
  alias Spark.Dsl.Verifier

  def verify(dsl_state) do
    dsl_state
    |> Verifier.get_entities([:steps])
    |> unnest()
    |> Enum.map(& &1.name)
    |> Enum.group_by(& &1)
    |> Enum.find_value({:ok, dsl_state}, fn
      {_, [_]} ->
        :ok

      {name, [_ | _] = dupes} ->
        {:error,
         Spark.Error.DslError.exception(
           path: [:flow, :steps],
           message:
             "Step names must be unique, but #{Enum.count(dupes)} steps share the name #{name}."
         )}
    end)
  end

  defp unnest(steps) do
    Enum.flat_map(steps, fn
      %{steps: steps} = step ->
        [step | unnest(steps)]

      step ->
        [step]
    end)
  end
end