dotfiles/modules/gaming/minecraft-server.nix

{ pkgs, ... }:

let

  localPort = 25564;
  publicPort = 25565;
  rconPort = 25575;
  rconPassword = "thiscanbeanything";

in {

  unfreePackages = [ "minecraft-server" ];

  services.minecraft-server = {
    enable = true;
    eula = true;
    declarative = true;
    whitelist = { };
    openFirewall = false;
    serverProperties = {
      server-port = localPort;
      difficulty = "normal";
      gamemode = "survival";
      white-list = false;
      enforce-whitelist = false;
      level-name = "world";
      motd = "Welcome!";
      pvp = true;
      player-idle-timeout = 30;
      generate-structures = true;
      max-players = 20;
      snooper-enabled = false;
      spawn-npcs = true;
      spawn-animals = true;
      spawn-monsters = true;
      allow-nether = true;
      allow-flight = false;
      enable-rcon = true;
      "rcon.port" = rconPort;
      "rcon.password" = rconPassword;
    };
  };

  networking.firewall.allowedTCPPorts = [ publicPort ];

  ## Automatically start and stop Minecraft server based on player connections

  # Adapted shamelessly from:
  # https://dataswamp.org/~solene/2022-08-20-on-demand-minecraft-with-systemd.html

  # Prevent Minecraft from starting by default
  systemd.services.minecraft-server = { wantedBy = pkgs.lib.mkForce [ ]; };

  # Listen for connections on the public port, to trigger the actual
  # listen-minecraft service.
  systemd.sockets.listen-minecraft = {
    wantedBy = [ "sockets.target" ];
    requires = [ "network.target" ];
    listenStreams = [ "${toString publicPort}" ];
  };

  # Proxy traffic to local port, and trigger hook-minecraft
  systemd.services.listen-minecraft = {
    path = [ pkgs.systemd ];
    requires = [ "hook-minecraft.service" "listen-minecraft.socket" ];
    after = [ "hook-minecraft.service" "listen-minecraft.socket" ];
    serviceConfig.ExecStart =
      "${pkgs.systemd.out}/lib/systemd/systemd-socket-proxyd 127.0.0.1:${
        toString localPort
      }";
  };

  # Start Minecraft if required and wait for it to be available
  # Then unlock the listen-minecraft.service
  systemd.services.hook-minecraft = {
    path = with pkgs; [ systemd libressl busybox ];

    # Start Minecraft and the auto-shutdown timer
    script = ''
      systemctl start minecraft-server.service
      systemctl start stop-minecraft.timer
    '';

    # Keep checking until the service is available
    postStart = ''
      for i in $(seq 60); do
        if ${pkgs.libressl.nc}/bin/nc -z 127.0.0.1 ${
          toString localPort
        } > /dev/null ; then
          exit 0
        fi
        ${pkgs.busybox.out}/bin/sleep 1
      done
      exit 1
    '';
  };

  # Run a player check on a schedule for auto-shutdown
  systemd.timers.stop-minecraft = {
    timerConfig = {
      OnCalendar = "*-*-* *:*:0/20"; # Every 20 seconds
      Unit = "stop-minecraft.service";
    };
    wantedBy = [ "timers.target" ];
  };

  # If no players are connected, then stop services and prepare to resume again
  systemd.services.stop-minecraft = {
    serviceConfig.Type = "oneshot";
    script = ''
      # Check when service was launched
      servicestartsec=$(
        date -d \
          "$(systemctl show \
               --property=ActiveEnterTimestamp \
               minecraft-server.service \
               | cut -d= -f2)" \
        +%s)

      # Calculate elapsed time
      serviceelapsedsec=$(( $(date +%s) - servicestartsec))

      # Ignore if service just started
      if [ $serviceelapsedsec -lt 180 ]
      then
        echo "Server was just started"
        exit 0
      fi

      PLAYERS=$(
        printf "list\n" \
          | ${pkgs.rcon.out}/bin/rcon -m \
          -H 127.0.0.1 -p ${builtins.toString rconPort} -P ${rconPassword} \
      )

      if echo "$PLAYERS" | grep "are 0 of a"
      then
        echo "Stopping server"
        systemctl stop minecraft-server.service
        systemctl stop hook-minecraft.service
        systemctl stop stop-minecraft.timer
      fi
    '';
  };

}