defmodule Tilly.BDD.StringBoolOps do
  @moduledoc """
  BDD operations module for sets of strings.
  Elements are strings, and leaf values are booleans.
  """

  @doc """
  Compares two strings.
  Returns `:lt`, `:eq`, or `:gt`.
  """
  def compare_elements(elem1, elem2) when is_binary(elem1) and is_binary(elem2) do
    cond do
      elem1 < elem2 -> :lt
      elem1 > elem2 -> :gt
      true -> :eq
    end
  end

  @doc """
  Checks if two strings are equal.
  """
  def equal_element?(elem1, elem2) when is_binary(elem1) and is_binary(elem2) do
    elem1 == elem2
  end

  @doc """
  Hashes a string.
  """
  def hash_element(elem) when is_binary(elem) do
    # erlang.phash2 is suitable for term hashing
    :erlang.phash2(elem)
  end

  @doc """
  The leaf value representing an empty set of strings (false).
  """
  def empty_leaf(), do: false

  @doc """
  The leaf value representing the universal set of strings (true).
  """
  def any_leaf(), do: true

  @doc """
  Checks if a leaf value represents an empty set.
  """
  def is_empty_leaf?(leaf_val) when is_boolean(leaf_val) do
    leaf_val == false
  end

  @doc """
  Computes the union of two leaf values.
  `typing_ctx` is included for interface consistency, but not used for boolean leaves.
  """
  def union_leaves(_typing_ctx, leaf1, leaf2) when is_boolean(leaf1) and is_boolean(leaf2) do
    leaf1 or leaf2
  end

  @doc """
  Computes the intersection of two leaf values.
  `typing_ctx` is included for interface consistency, but not used for boolean leaves.
  """
  def intersection_leaves(_typing_ctx, leaf1, leaf2)
      when is_boolean(leaf1) and is_boolean(leaf2) do
    leaf1 and leaf2
  end

  @doc """
  Computes the negation of a leaf value.
  `typing_ctx` is included for interface consistency, but not used for boolean leaves.
  """
  def negation_leaf(_typing_ctx, leaf) when is_boolean(leaf) do
    not leaf
  end

  # def difference_leaves(_typing_ctx, leaf1, leaf2) when is_boolean(leaf1) and is_boolean(leaf2) do
  #   leaf1 and (not leaf2)
  # end

  @doc """
  Tests a leaf value to determine if it represents an empty, full, or other set.
  Returns `:empty`, `:full`, or `:other`.
  """
  def test_leaf_value(true), do: :full
  def test_leaf_value(false), do: :empty
  # def test_leaf_value(_other), do: :other
end