util functions in Elixir for Chinese ID

cn_id.ex

defmodule CnId do

  defp parse!(id) do
    <<adcode :: 6-bytes, year :: 4-bytes, month :: 2-bytes, day :: 2-bytes, seq_code :: 3-bytes, check_code :: 1-bytes>> = id
    
    %{
      adcode: adcode,
      birthday: Date.from_iso8601!("#{year}-#{month}-#{day}"),
      seq_code: seq_code,
      check_code: check_code
    }
  end
  
  def checksum(id) do
    <<info :: 17-bytes, check_code :: 1-bytes>> = id
    
    Stream.iterate(18, &(&1 - 1)) 
    |> Stream.zip(String.to_charlist(info))
    |> Enum.reduce(0, fn {index, char}, acc ->
      n = char - ?0
      acc + n * rem(round(:math.pow(2, index - 1)), 11)
    end)
    |> (&(rem(12 - rem(&1, 11), 11))).()
    |> (&(if &1 < 10, do: to_string(&1), else: "X")).()
  end
  
  def validate?(id) do
    <<info :: 17-bytes, check_code :: 1-bytes>> = id
    checksum(id) == check_code
  end
  
  def adcode(id) do
    parse!(id).adcode
  end
  
  def seq_code(id) do
    parse!(id).seq_code
  end
  
  def birthday(id) do
    parse!(id).birthday
  end
  
  def gender(id) do
    seq_code(id)
    |> Integer.parse
    |> elem(0)
    |> rem(2)
    |> (&(if &1 == 0, do: :female, else: :male)).()
  end
  
end