# The games stack for the living-room machine: the Steam session that the TV
# boots into, RetroArch with its cores, Clone Hero, and the controller plumbing.
#
# Session model. greetd (from ../../modules/sway.nix, which enables it for
# ReGreet) gets an `initial_session`, so the machine autologins into the
# gamescope Steam session at boot -- no keyboard, no greeter, straight to Big
# Picture. Quitting Steam drops back to greetd's `default_session`, i.e. ReGreet,
# where the ordinary Sway session can be picked for keyboard-and-mouse work.
{ pkgs, ... }:

let
  # The account the television autologins as. Must match the user declared for
  # this host in the flake host table.
  tvUser = "lyrathorpe";

  # Games library root. Deliberately outside any home directory: content is
  # bulky, is the thing most likely to move to its own disk, and is shared
  # between Steam, RetroArch and Clone Hero rather than owned by one of them.
  # Mounting a second drive at this path is the only change that needs.
  gamesRoot = "/srv/games";

  # One ROM directory per emulated system. Names follow the libretro/ES-DE
  # convention so a scraper or a second frontend recognises them without
  # renaming anything.
  romSystems = [
    "nes"
    "snes"
    "gb"
    "gbc"
    "gba"
    "n64"
    "nds"
    "gc"
    "wii"
    "mastersystem"
    "gamegear"
    "megadrive"
    "sega32x"
    "segacd"
    "saturn"
    "dreamcast"
    "psx"
    "ps2"
    "psp"
    "arcade"
    "dos"
  ];

  # Everything under the root that is not a ROM directory. RetroArch is pointed
  # at these below; Steam and Clone Hero have to be told about theirs in their
  # own UIs (see docs/hosts/console.md).
  libraryDirs = [
    "bios" # RetroArch system directory: BIOS and firmware images
    "saves" # in-game saves
    "states" # save states
    "playlists"
    "screenshots"
    "thumbnails"
    "steam" # add as a Steam library folder from the client
    "clonehero/songs"
    "clonehero/backgrounds"
  ];

  # RetroArch and the cores this machine is expected to run. The wrapper already
  # points RetroArch at the packaged assets, core info and joypad autoconfig
  # profiles; `settings` here is merged on top of those.
  retroarch = pkgs.retroarch-bare.wrapper {
    cores = with pkgs.libretro; [
      # Nintendo
      nestopia # NES
      snes9x # SNES
      gambatte # Game Boy / Color
      mgba # Game Boy Advance
      mupen64plus # Nintendo 64
      melonds # Nintendo DS
      dolphin # GameCube / Wii
      # Sega
      genesis-plus-gx # Master System / Game Gear / Mega Drive
      picodrive # 32X / Mega CD
      beetle-saturn # Saturn
      flycast # Dreamcast / NAOMI
      # Sony
      beetle-psx-hw # PlayStation, hardware renderer
      pcsx2 # PlayStation 2 (LRPS2); needs a PS2 BIOS in RetroArch's system dir
      ppsspp # PSP
      # Arcade and PC
      fbneo
      mame2003-plus
      dosbox-pure
    ];
    settings = {
      # Applied on every launch via --appendconfig, so these three are fixed
      # policy rather than saved preferences: changing them in the UI will not
      # stick. Everything else stays user-editable as usual.
      #
      # Ozone is the controller-navigable menu; the TV has no keyboard.
      menu_driver = "ozone";
      video_fullscreen = "true";
      # L3+R3 opens the RetroArch menu from inside a running core
      # (INPUT_COMBO_L3_R3). Without a pad combo there is no way to exit a game
      # without a keyboard, and no retro system this box emulates has L3/R3 on
      # its own controller, so the binding cannot collide with a game.
      input_menu_toggle_gamepad_combo = "2";

      # Point RetroArch at the shared library instead of scattering content and
      # state through ~/.config/retroarch. Key names are RetroArch's own; an
      # unrecognised key in an appended config is ignored silently, so they are
      # worth keeping in step with upstream.
      system_directory = "${gamesRoot}/bios";
      savefile_directory = "${gamesRoot}/saves";
      savestate_directory = "${gamesRoot}/states";
      playlist_directory = "${gamesRoot}/playlists";
      screenshot_directory = "${gamesRoot}/screenshots";
      thumbnails_directory = "${gamesRoot}/thumbnails";
      # Where the content browser opens, so loading a game is a couple of
      # D-pad presses rather than a walk up from the filesystem root.
      rgui_browser_directory = "${gamesRoot}/roms";
    };
  };
in
{
  programs.steam = {
    enable = true;

    # Registers the "Steam" wayland session (gamescope wrapping Steam in tenfoot
    # mode) with the display manager and installs the steam-gamescope launcher.
    gamescopeSession.enable = true;
    gamescopeSession.env = {
      # gamescope has to be pointed at NVIDIA's GBM implementation and GLX
      # vendor explicitly; on the proprietary driver it otherwise fails to get a
      # usable device and the session dies at startup.
      GBM_BACKEND = "nvidia-drm";
      __GLX_VENDOR_LIBRARY_NAME = "nvidia";
    };

    # Remote Play and local network game transfers are the point of a TV box on
    # the same LAN as a desktop; both need their ports open.
    remotePlay.openFirewall = true;
    localNetworkGameTransfers.openFirewall = true;

    # Proton-GE, selectable per title in Steam's compatibility settings. Covers
    # the titles where Valve's Proton lags on codecs and anti-cheat shims. The
    # module puts its steamcompattool output on STEAM_EXTRA_COMPAT_TOOLS_PATHS,
    # which is what makes it appear in the client's Proton version list.
    extraCompatPackages = [ pkgs.proton-ge-bin ];

    # Winetricks against a Proton prefix: the standard repair tool when a title
    # needs a runtime (dotnet, vcrun, Media Foundation) that Proton does not ship.
    protontricks.enable = true;
  };

  # Proton prerequisites beyond what programs.steam already arranges.
  #
  # Already covered by the steam module, recorded here so it is not re-litigated:
  # hardware.graphics 32-bit (the lib32 NVIDIA userspace Proton's 32-bit prefixes
  # need), Steam's udev rules, 32-bit PipeWire, and the system fonts Wine renders
  # with (Liberation and DejaVu arrive with fonts.enableDefaultPackages).
  # vm.max_map_count is 1048576 in the nixpkgs default sysctls, which is above
  # what DX12/Unreal titles need -- no override required.
  #
  # What is not covered: esync opens one eventfd per Wine sync object and runs
  # out against systemd's default 524288 hard limit in the heaviest titles.
  # Raise the hard limit only; the soft limit stays at the default, because
  # lifting that breaks select()-based programs elsewhere on the system.
  systemd.settings.Manager.DefaultLimitNOFILE = "1024:1048576";

  # capSysNice lets gamescope raise its own scheduling priority, which is what
  # keeps the compositor smooth while a game saturates the GPU. It installs
  # gamescope as a setcap wrapper instead of a plain systemPackages entry;
  # /run/wrappers/bin precedes the system profile on PATH, so steam-gamescope
  # still resolves it.
  programs.gamescope = {
    enable = true;
    capSysNice = true;
  };

  # Applies the performance CPU governor (and drops it again) around games that
  # ask for it; Steam's Proton builds and most native titles do.
  programs.gamemode.enable = true;

  # Autologin into the Steam session. The launcher is not exposed as a package
  # by the steam module -- it is built inside it and added to
  # environment.systemPackages -- so reference it through the system profile.
  # greetd's `restart` option defaults to false once initial_session is set,
  # which is what stops a logout from looping straight back into autologin.
  services.greetd.settings.initial_session = {
    command = "/run/current-system/sw/bin/steam-gamescope";
    user = tvUser;
  };

  # Controllers.
  #
  # Xbox One/Series pads over Bluetooth need xpadneo: the in-kernel xpad driver
  # does not handle them well over BT (wrong button mapping, no rumble). The
  # module turns on bluez itself; powerOnBoot is set below so the adapter is up
  # before the Steam session starts and a pad can reconnect unattended.
  #
  # Everything else is in-kernel and needs no configuration: wired Xbox 360 pads
  # (and the 360 wireless receiver) via xpad, DualSense/DualShock 4 via
  # hid-playstation over USB and Bluetooth, and Clone Hero guitars as plain USB
  # HID gamepads. xpadneo does not contend with xpad -- it binds Bluetooth HID
  # devices, and the 360 pad is not HID-compliant. hardware.xone is deliberately
  # left off: it blacklists xpad, which would break the 360 pads.
  #
  # hidraw access for the PlayStation pads (LED, battery, dualsensectl) comes
  # from Steam's udev rules, which programs.steam enables via
  # hardware.steam-hardware.
  hardware.xpadneo.enable = true;
  hardware.bluetooth = {
    enable = true;
    powerOnBoot = true;
    # Battery level reporting for Bluetooth gamepads is still behind bluez's
    # experimental flag.
    settings.General.Experimental = true;
  };

  # The games library, created at boot so the directories exist before anything
  # tries to write into them. Mode 2775 is setgid: the owning group is carried
  # onto anything created inside, so a second account (or an rsync from another
  # machine) does not end up with files the TV user cannot write. Directories
  # are created if missing and otherwise left alone -- nothing here removes or
  # rewrites content.
  systemd.tmpfiles.rules =
    let
      dir = path: "d ${path} 2775 ${tvUser} users -";
    in
    [
      (dir gamesRoot)
      (dir "${gamesRoot}/roms")
    ]
    ++ map (system: dir "${gamesRoot}/roms/${system}") romSystems
    ++ map (sub: dir "${gamesRoot}/${sub}") libraryDirs;

  # 32-bit ALSA for the older native titles that talk to ALSA directly rather
  # than through the PulseAudio shim; programs.steam derives
  # pipewire.alsa.support32Bit from this. PipeWire itself and the Pulse shim
  # come from ../../modules/workstation.nix.
  services.pipewire.alsa.enable = true;

  environment.systemPackages = [
    retroarch
    pkgs.clonehero
    pkgs.dualsensectl # DualSense LED/battery/mic control from the shell
    pkgs.mangohud # FPS/frametime overlay; use `mangohud %command%` in Steam
    pkgs.vulkan-tools # vulkaninfo, for checking the 32/64-bit ICDs Proton needs
  ];
}