nixos/hosts/yarn/forza-trigger/default.nix

{
  config,
  lib,
  pkgs,
  username,
  ...
}:
# Forza Horizon 4 / 5 → DualSense adaptive trigger bridge.
#
# Forza emits a fixed-format UDP telemetry stream ("Data Out") at 60 Hz on a
# user-configured port. We listen on that port, parse each packet via fdp
# (nettrom/forza_motorsport, MIT), and drive the PS5 DualSense's adaptive
# triggers via pydualsense (PyPI, MIT) which talks HID over hidraw.
#
# Setup on the user side, once enabled here:
#   - plug the DualSense in over USB and disable Steam Input for the
#     controller (Settings → Controller → "PlayStation Configuration Support":
#     OFF). Bluetooth works too but the udev/hidraw path is more reliable
#     over USB.
#   - in Forza, HUD options \u2192 set Data Out: ON, Data Out IP: 127.0.0.1,
#     Data Out IP Port: 5300, and (FM7 only) Data Out Packet Format: CAR DASH.
#
# System-interaction notes:
#   - With multiple DualSense controllers connected, pydualsense picks one
#     non-deterministically (`# TODO: implement multiple controllers working`
#     in pydualsense's source). Forza Horizon is single-player so this is
#     usually fine. If you need to pin a specific controller, the cleanest
#     route is monkey-patching `pydualsense.__find_device`.
#   - The included `dualsensectl` will be overwritten by our BG thread within
#     ~4 ms; use `systemctl --user stop forza-trigger` first when debugging.
#   - Hot-plug recovery happens in-process: the daemon polls pydualsense's BG
#     thread liveness and re-runs `pydualsense.init()` on disconnect. systemd's
#     `Restart=on-failure` exists only as a crash-recovery safety net.
let
  cfg = config.services.forzaTrigger;
  python = pkgs.python3;

  # CFFI bindings to libhidapi. Upstream is flok/hidapi-cffi published on
  # PyPI under the name `hidapi-usb`. The shipped hidapi.py picks a libhidapi
  # soname via ffi.dlopen() — we substitute absolute store paths so the
  # interpreter inside our wrapped python env can find it without
  # LD_LIBRARY_PATH gymnastics.
  hidapi-usb = python.pkgs.buildPythonPackage rec {
    pname = "hidapi-usb";
    version = "0.3.2";
    format = "setuptools";

    # PyPI's project URL slug uses a hyphen (`hidapi-usb`) but the sdist file
    # itself is PEP-625-normalized to an underscore (`hidapi_usb-…`). Stock
    # fetchPypi assumes they match — they don't here, so fetch by direct URL.
    src = pkgs.fetchurl {
      url = "https://files.pythonhosted.org/packages/55/80/960ae94b615e26a7d1aeebe8e9fefda2f25608bf1016f9aec268b328c35e/hidapi_usb-${version}.tar.gz";
      hash = "sha256-oxp+2i+qqYd1uwiS2Dh8/PzO62iYQQXpR936MnDIFk0=";
    };

    propagatedBuildInputs = [ python.pkgs.cffi ];

    postPatch = ''
      substituteInPlace hidapi.py \
        --replace-fail "'libhidapi-hidraw.so'," "'${pkgs.hidapi}/lib/libhidapi-hidraw.so'," \
        --replace-fail "'libhidapi-hidraw.so.0'," "'${pkgs.hidapi}/lib/libhidapi-hidraw.so.0',"
    '';

    pythonImportsCheck = [ "hidapi" ];

    meta = {
      description = "CFFI wrapper for hidapi (used by pydualsense)";
      homepage = "https://github.com/flok/hidapi-cffi";
      license = lib.licenses.bsd3;
    };
  };

  pydualsense = python.pkgs.buildPythonPackage rec {
    pname = "pydualsense";
    version = "0.7.5";
    format = "pyproject";

    src = python.pkgs.fetchPypi {
      pname = "pydualsense";
      inherit version;
      hash = "sha256-YgX8AJE4f8p7geKT3xlCD0Mlh1GcyHpBz4rEIqdwKgs=";
    };

    nativeBuildInputs = [ python.pkgs.poetry-core ];
    propagatedBuildInputs = [ hidapi-usb ];

    pythonImportsCheck = [ "pydualsense" ];

    meta = {
      description = "Control your PS5 DualSense controller from Python";
      homepage = "https://github.com/flok/pydualsense";
      license = lib.licenses.mit;
    };
  };

  # Single-file Forza UDP packet parser. Pinned to a known-good commit; the
  # repo is dormant (last commit 2021) but the FH4 packet layout is frozen
  # and FH5 reuses it byte-for-byte.
  fdp = python.pkgs.buildPythonPackage {
    pname = "fdp";
    version = "0-unstable-2021-05-28";
    format = "other";

    src = pkgs.fetchurl {
      url = "https://raw.githubusercontent.com/nettrom/forza_motorsport/61845cb7ff4082211292a51ce3c49edbfd2d6503/fdp.py";
      hash = "sha256-osFaVF9VaEzU4dp3x6KN6OF7SXsd9ZBwvilU+xTT7mM=";
    };

    dontUnpack = true;

    installPhase = ''
      runHook preInstall
      install -Dm644 $src $out/${python.sitePackages}/fdp.py
      runHook postInstall
    '';

    pythonImportsCheck = [ "fdp" ];

    meta = {
      description = "ForzaDataPacket — Forza Motorsport / Horizon UDP packet parser";
      homepage = "https://github.com/nettrom/forza_motorsport";
      license = lib.licenses.mit;
    };
  };

  forzaTrigger = pkgs.writers.writePython3Bin "forza-trigger" {
    libraries = [
      pydualsense
      fdp
    ];
    # The wrapped binary doesn't need style enforcement — readability of
    # the source file is what matters, and that lives in forza_trigger.py.
    doCheck = false;
  } (builtins.readFile ./forza_trigger.py);

in
{
  options.services.forzaTrigger = {
    enable = lib.mkEnableOption "Forza Horizon → DualSense adaptive trigger bridge";

    user = lib.mkOption {
      type = lib.types.str;
      default = username;
      description = ''
        User the trigger daemon runs as. Must be the user playing Forza so
        the DualSense's hidraw uaccess ACL applies.
      '';
    };

    port = lib.mkOption {
      type = lib.types.port;
      default = 5300;
      description = ''
        UDP port the daemon listens on for Forza Data Out packets. Must
        match the value configured in Forza's HUD options.
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    # uaccess hands /dev/hidraw* of the connected PS5 DualSense to the
    # active-seat user via ACL. Steam ships near-identical rules; declaring
    # them here keeps the module self-contained (and works even if Steam
    # isn't running).
    services.udev.extraRules = ''
      # PS5 DualSense (USB)
      KERNEL=="hidraw*", ATTRS{idVendor}=="054c", ATTRS{idProduct}=="0ce6", MODE="0660", TAG+="uaccess"
      # PS5 DualSense Edge (USB)
      KERNEL=="hidraw*", ATTRS{idVendor}=="054c", ATTRS{idProduct}=="0df2", MODE="0660", TAG+="uaccess"
      # PS5 DualSense (Bluetooth)
      KERNEL=="hidraw*", KERNELS=="*054C:0CE6*", MODE="0660", TAG+="uaccess"
      # PS5 DualSense Edge (Bluetooth)
      KERNEL=="hidraw*", KERNELS=="*054C:0DF2*", MODE="0660", TAG+="uaccess"
    '';

    environment.systemPackages = [
      forzaTrigger
      # CLI companion for sanity-checking the controller (battery, lightbar,
      # raw trigger modes, monitor add/remove events).
      pkgs.dualsensectl
    ];

    # User-level service so it inherits the seat-bound uaccess ACL on
    # /dev/hidraw* and dies cleanly when the user logs out.
    systemd.user.services.forza-trigger = {
      description = "Forza Horizon → DualSense adaptive trigger bridge";
      wantedBy = [ "default.target" ];
      after = [ "graphical-session.target" ];
      serviceConfig = {
        ExecStart = "${forzaTrigger}/bin/forza-trigger --host 127.0.0.1 --port ${toString cfg.port}";
        Restart = "on-failure";
        RestartSec = 3;
      };
    };
  };
}