defmodule Tilly.Type do
  @moduledoc """
  Defines the structure of a Type Descriptor (`Descr`) and provides
  helper functions for creating fundamental type descriptors.

  A Type Descriptor is a map representing a type. Each field in the map
  corresponds to a basic kind of type component (e.g., atoms, integers, pairs)
  and holds a BDD node ID. These BDDs represent the set of values
  allowed for that particular component of the type.
  """

  alias Tilly.BDD

  @doc """
  Returns a `Descr` map representing the empty type (Nothing).
  All BDD IDs in this `Descr` point to the canonical `false` BDD node.
  The `typing_ctx` is passed for consistency but not modified by this function.
  """
  def empty_descr(_typing_ctx) do
    false_id = BDD.false_node_id()

    %{
      atoms_bdd_id: false_id,
      integers_bdd_id: false_id,
      strings_bdd_id: false_id,
      pairs_bdd_id: false_id,
      records_bdd_id: false_id,
      functions_bdd_id: false_id,
      absent_marker_bdd_id: false_id
      # Add other kinds as needed, e.g., for abstract types
    }
  end

  @doc """
  Returns a `Descr` map representing the universal type (Any).
  All BDD IDs in this `Descr` point to the canonical `true` BDD node.
  The `typing_ctx` is passed for consistency but not modified by this function.
  """
  def any_descr(_typing_ctx) do
    true_id = BDD.true_node_id()

    %{
      atoms_bdd_id: true_id,
      integers_bdd_id: true_id,
      strings_bdd_id: true_id,
      pairs_bdd_id: true_id,
      records_bdd_id: true_id,
      functions_bdd_id: true_id,
      # For 'Any', absence is typically not included unless explicitly modeled.
      # If 'Any' should include the possibility of absence, this would be true_id.
      # For now, let's assume 'Any' means any *value*, so absence is false.
      # This can be refined based on the desired semantics of 'Any'.
      # CDuce 'Any' does not include 'Absent'.
      absent_marker_bdd_id: BDD.false_node_id()
    }
  end
end