truth_table

defmodule TruthTable do
  @moduledoc """
  Documentation for TruthTable.
  """
  use Bitwise, only_operators: true

  @doc """
  Generate all combinations of `size` boolean values.
  There is no order guarantee.

  ## Examples

      iex> 2 |> TruthTable.inputs() |> MapSet.new()
      MapSet.new([[false, false], [false, true], [true, true], [true, false]])

  """
  def inputs(size) when is_integer(size) and size >= 0 do
    1
    |> Bitwise.<<<(size)
    |> Kernel.-(1)
    |> Range.new(0)
    |> Enum.map(&generate_row(size, &1, []))
  end

  def inputs(size) do
    raise ArgumentError, "Expected non-negative integer, got: #{inspect(size)}"
  end

  defp generate_row(0, _value, row) do
    row
  end

  defp generate_row(count, value, row) do
    generate_row(count - 1, value >>> 1, [invert(value &&& 1) | row])
  end

  defp invert(0), do: true
  defp invert(_), do: false
end