amethyst/lib/servers/play.ex

# Amethyst - An experimental Minecraft server written in Elixir.
# Copyright (C) 2024 KodiCraft
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

defmodule Amethyst.Server.Play do
  @moduledoc """
  This module contains the logic for the Play stage of the server.
  """
  require Logger
  use Amethyst.Server

  alias Amethyst.Minecraft.Read
  alias Amethyst.Minecraft.Write

  @impl true
  def init(state) do
    state
  end

  ## DESERIALIZATION
  @impl true

  def deserialize(type, _) do
    raise RuntimeError, "Got unknown packet type #{type}!"
  end

  ## SERIALIZATION
  @impl true
  # Login https://wiki.vg/Protocol#Login_(play)
  def serialize({:login, eid, hardcore, dimensions,
    max_players, view_distance, simulation_distance,
    reduce_debug, enable_respawn_screen, limited_crafting,
    dim_type, dim_name, hashed_seed, gamemode, prev_gm,
    is_debug, is_flat, death_loc, portal_cooldown, enforce_chat}) do
      # TODO: this singlehandedly made me regret not making the write API better, please rework :(
      Write.varint(0x2B) <>
      <<eid::big-signed-32>> <> if(hardcore, do: <<1::big-8>>, else: <<0::big-8>>) <>
      Write.varint(length(dimensions)) <> Enum.reduce(dimensions, "", fn dim, acc -> acc <> Write.string(dim) end) <>
      Write.varint(max_players) <> Write.varint(view_distance) <> Write.varint(simulation_distance) <> if(reduce_debug, do: <<1::big-8>>, else: <<0::big-8>>) <>
      if(enable_respawn_screen, do: <<1::big-8>>, else: <<0::big-8>>)
      if(limited_crafting, do: <<1::big-8>>, else: <<0::big-8>>) <> Write.varint(dim_type) <> Write.string(dim_name) <>
      hashed_seed <> <<gamemode_id(gamemode)::unsigned-big-8>> <> <<gamemode_id(prev_gm)::signed-big-8>> <>
      if(is_debug, do: <<1::big-8>>, else: <<0::big-8>>) <> if(is_flat, do: <<1::big-8>>, else: <<0::big-8>>) <>
      if(death_loc == nil, do: <<0::big-8>>, else: <<1::big-8>> <> Write.string(elem(death_loc, 0)) <> Write.position(elem(death_loc, 1))) <>
      Write.varint(portal_cooldown) <> if(enforce_chat, do: <<1::big-8>>, else: <<0::big-8>>)
    end
  def serialize(packet) do
    raise ArgumentError, "Tried serializing unknown packet #{inspect(packet)}"
  end

  ## HANDLING
  @impl true
  def handle(tuple, _, state) do
    Logger.error("Unhandled but known packet #{elem(tuple, 0)}")
    {:unhandled, state}
  end

  defp gamemode_id(gm) do
    case gm do
      nil -> -1
      :survival -> 0
      :creative -> 1
      :adventure -> 2
      :spectator -> 3
    end
  end
end