defmodule BinStruct.FlagsReader do

  @moduledoc """
  Useful in `registered_callbacks` when library can't achieve automatic type conversion.

  ```elixir
  iex> flags = [{0x01, :flag_a}, {0x02, :flag_b}]
  ...> BinStruct.FlagsReader.read_flags_from_integer(flags, 0x01)
  [:flag_a]
  ```
  """

  def read_flags_from_integer([], _integer), do: []

  def read_flags_from_integer([{flag_mask, flag} | rest], integer) do

    is_set = Bitwise.band(integer, flag_mask) > 0

    if is_set do
      [ flag | read_flags_from_integer(rest, integer)]
    else
      read_flags_from_integer(rest, integer)
    end

  end

end