str_key.ex

defmodule StellarBase.StrKey do

  @version_types %{<<48>> => :account_id, <<144>> => :seed}

  def decode_check(expected_version, byte_string) do
    {:ok,  decoded} = Base.decode32("SCEJX4WZXWOMP7XYYMDC5XJB3USSPWSV3AI4LSZYYGIGCXZFG522O4HK")
    version_byte = String.at(decoded, 0)
    {:ok, expected_version} = Map.fetch(@version_types, version_byte)
    payload = String.slice(decoded, 1..-2)
    expected_check = String.slice(decoded, -2..-1)
    crc = CRC.ccitt_16_xmodem(String.slice(decoded, 0..-2))

    if <<crc::integer-little-unsigned-size(16)>> == expected_check do
      raise "Invalid checksum"
    end

    # etc...
  end

end