bacstack

defmodule BACnet.Protocol.APDU.SimpleACK do
  @moduledoc """
  Simple ACK APDUs are used to convey the information contained
  in a positive service response primitive that contains no other
  information except that the service request was successfully carried out.

  This module has functions for encoding Simple ACK APDUs.
  Decoding is handled by `BACnet.Protocol.APDU`.

  This module implements the `BACnet.Stack.EncoderProtocol`.
  """

  alias BACnet.Protocol.Constants

  @typedoc """
  Represents the Application Data Unit (APDU) Simple ACK.

  To allow forward compatibility, service is allowed to be an integer.
  """
  @type t :: %__MODULE__{
          invoke_id: 0..255,
          service: Constants.confirmed_service_choice() | non_neg_integer()
        }

  @fields [
    :invoke_id,
    :service
  ]
  @enforce_keys @fields
  defstruct @fields

  @encoder_module Module.concat([BACnet.Stack.EncoderProtocol, __MODULE__])

  @doc """
  Encodes the Simple ACK APDU into binary data.
  """
  @spec encode(t()) :: {:ok, iodata()} | {:error, Exception.t()}
  def encode(%__MODULE__{} = apdu) do
    res = @encoder_module.encode(apdu)
    {:ok, res}
  rescue
    e -> {:error, e}
  end

  defimpl BACnet.Stack.EncoderProtocol do
    alias BACnet.Protocol.Constants
    require Constants

    @doc """
    Whether the struct expects a reply (i.e. Confirmed Service Request).

    This is useful for NPCI calculation.
    """
    @spec expects_reply(@for.t()) :: boolean()
    def expects_reply(%@for{} = _apdu), do: false

    @doc """
    Whether the struct is a request.
    """
    @spec is_request(@for.t()) :: boolean()
    def is_request(%@for{} = _apdu), do: false

    @doc """
    Whether the struct is a response.
    """
    @spec is_response(@for.t()) :: boolean()
    def is_response(%@for{} = _apdu), do: true

    @spec encode(@for.t()) :: iodata()
    def encode(
          %@for{
            invoke_id: invoke_id
          } = apdu
        ) do
      unless invoke_id >= 0 and invoke_id <= 255 do
        raise ArgumentError,
              "Invoke ID must be between 0 and 255 inclusive, got: #{inspect(invoke_id)}"
      end

      service =
        if is_atom(apdu.service) do
          Constants.by_name!(:confirmed_service_choice, apdu.service)
        else
          apdu.service
        end

      <<Constants.macro_by_name(:pdu_type, :simple_ack)::size(4), 0::size(4), invoke_id::size(8),
        service::size(8)>>
    end

    @spec supports_segmentation(@for.t()) :: boolean()
    def supports_segmentation(_apdu), do: false

    @spec encode_segmented(@for.t(), integer()) :: [binary()]
    def encode_segmented(%@for{} = _t, _apdu_size) do
      raise "Illegal function call, APDU can not be segmented"
    end
  end
end