odinsea-elixir/lib/odinsea/net/packet/out.ex

defmodule Odinsea.Net.Packet.Out do
  @moduledoc """
  Outgoing packet writer ported from Java OutPacket.
  Handles little-endian encoding of MapleStory packet data.
  """

  defstruct data: <<>>

  @type t :: %__MODULE__{
          data: iodata()
        }

  @doc """
  Creates a new outgoing packet.
  """
  @spec new() :: t()
  def new do
    %__MODULE__{data: []}
  end

  @doc """
  Creates a new outgoing packet with an opcode.
  """
  @spec new(integer()) :: t()
  def new(opcode) when is_integer(opcode) do
    %__MODULE__{data: [<<opcode::signed-integer-little-16>>]}
  end

  @doc """
  Encodes a byte to the packet.
  """
  @spec encode_byte(t(), integer()) :: t()
  def encode_byte(%__MODULE__{data: data}, value) when is_integer(value) do
    %__MODULE__{data: [data | <<value::signed-integer-little-8>>]}
  end

  @doc """
  Encodes a short (2 bytes) to the packet.
  """
  @spec encode_short(t(), integer()) :: t()
  def encode_short(%__MODULE__{data: data}, value) when is_integer(value) do
    %__MODULE__{data: [data | <<value::signed-integer-little-16>>]}
  end

  @doc """
  Encodes an int (4 bytes) to the packet.
  """
  @spec encode_int(t(), integer()) :: t()
  def encode_int(%__MODULE__{data: data}, value) when is_integer(value) do
    %__MODULE__{data: [data | <<value::signed-integer-little-32>>]}
  end

  @doc """
  Encodes a long (8 bytes) to the packet.
  """
  @spec encode_long(t(), integer()) :: t()
  def encode_long(%__MODULE__{data: data}, value) when is_integer(value) do
    %__MODULE__{data: [data | <<value::signed-integer-little-64>>]}
  end

  @doc """
  Encodes a MapleStory ASCII string.
  Format: [2-byte length][ASCII bytes]
  """
  @spec encode_string(t(), String.t()) :: t()
  def encode_string(%__MODULE__{data: data}, value) when is_binary(value) do
    length = byte_size(value)
    %__MODULE__{data: [data | <<length::signed-integer-little-16, value::binary>>]}
  end

  @doc """
  Encodes a boolean (1 byte, 0 = false, 1 = true).
  """
  @spec encode_bool(t(), boolean()) :: t()
  def encode_bool(%__MODULE__{data: data}, true) do
    %__MODULE__{data: [data | <<1::signed-integer-little-8>>]}
  end

  def encode_bool(%__MODULE__{data: data}, false) do
    %__MODULE__{data: [data | <<0::signed-integer-little-8>>]}
  end

  @doc """
  Encodes a raw buffer to the packet.
  """
  @spec encode_buffer(t(), binary()) :: t()
  def encode_buffer(%__MODULE__{data: data}, buffer) when is_binary(buffer) do
    %__MODULE__{data: [data | buffer]}
  end

  @doc """
  Encodes a fixed-size buffer, padding with zeros if necessary.
  """
  @spec encode_fixed_buffer(t(), binary(), non_neg_integer()) :: t()
  def encode_fixed_buffer(%__MODULE__{data: data}, buffer, size) when is_binary(buffer) do
    current_size = byte_size(buffer)

    padding =
      if current_size < size do
        <<0::size((size - current_size) * 8)>>
      else
        <<>>
      end

    truncated = binary_part(buffer, 0, min(current_size, size))
    %__MODULE__{data: [data | truncated]}
    |> then(&%__MODULE__{data: [&1.data | padding]})
  end

  @doc """
  Encodes a timestamp (current time in milliseconds).
  """
  @spec encode_timestamp(t()) :: t()
  def encode_timestamp(%__MODULE__{data: data}) do
    timestamp = System.system_time(:millisecond)
    %__MODULE__{data: [data | <<timestamp::signed-integer-little-64>>]}
  end

  @doc """
  Encodes a file time (Windows FILETIME format).
  """
  @spec encode_filetime(t(), integer()) :: t()
  def encode_filetime(%__MODULE__{data: data}, value) when is_integer(value) do
    %__MODULE__{data: [data | <<value::signed-integer-little-64>>]}
  end

  @doc """
  Encodes a file time for "zero" (infinite/no expiration).
  """
  @spec encode_filetime_zero(t()) :: t()
  def encode_filetime_zero(%__MODULE__{data: data}) do
    %__MODULE__{data: [data | <<0x00::64>>]}
  end

  @doc """
  Encodes a file time for "infinite".
  """
  @spec encode_filetime_infinite(t()) :: t()
  def encode_filetime_infinite(%__MODULE__{data: data}) do
    %__MODULE__{data: [data | <<0xDD15F1C0::little-32, 0x11CE::little-16, 0xC0C0::little-16>>]}
  end

  @doc """
  Encodes a position (2 ints: x, y).
  """
  @spec encode_position(t(), {integer(), integer()}) :: t()
  def encode_position(%__MODULE__{data: data}, {x, y}) do
    %__MODULE__{data: [data | <<x::signed-integer-little-32, y::signed-integer-little-32>>]}
  end

  @doc """
  Encodes a short position (2 shorts: x, y).
  """
  @spec encode_short_position(t(), {integer(), integer()}) :: t()
  def encode_short_position(%__MODULE__{data: data}, {x, y}) do
    %__MODULE__{data: [data | <<x::signed-integer-little-16, y::signed-integer-little-16>>]}
  end

  @doc """
  Returns the packet as a binary.
  """
  @spec to_binary(t()) :: binary()
  def to_binary(%__MODULE__{data: data}) do
    IO.iodata_to_binary(data)
  end

  @doc """
  Returns the packet as iodata (for efficient writing).
  """
  @spec to_iodata(t()) :: iodata()
  def to_iodata(%__MODULE__{data: data}) do
    data
  end

  @doc """
  Converts the packet to a hex string for debugging.
  """
  @spec to_string(t()) :: String.t()
  def to_string(%__MODULE__{data: data}) do
    data |> IO.iodata_to_binary() |> Odinsea.Net.Hex.encode()
  end

  @doc """
  Returns the current packet size in bytes.
  """
  @spec length(t()) :: non_neg_integer()
  def length(%__MODULE__{data: data}) do
    IO.iodata_length(data)
  end
end