{ config, lib, pkgs, ... }:

let
  pivccu-modules = config.boot.kernelPackages.callPackage ({ stdenv, fetchFromGitHub, kernel }: stdenv.mkDerivation rec {
    pname = "pivccu-modules";
    version = "master";

    src = fetchFromGitHub {
      owner = "alexreinert";
      repo = "piVCCU";
      rev = "master"; 
      # Ensure this matches the hash you got earlier
      sha256 = "sha256-cXvrLcASU/2nsfJBf+cVtC4JnAq4G5JFzcFgj5ztThc=";
    };

    # Set the source root to the kernel subdirectory
    sourceRoot = "${src.name}/kernel";

    hardeningDisable = [ "pic" "format" ];
    nativeBuildInputs = kernel.moduleBuildDependencies;

    # 1. FORCE delete the upstream Makefile (which causes the build error)
    # 2. Create a clean Makefile that only builds the modules we need
    postPatch = ''
      rm -f Makefile
      echo "obj-m += eq3_char_loop.o plat_eq3ccu2.o" > Makefile
    '';

    # 3. Explicitly point to the kernel build directory
    makeFlags = [
      "KERNEL_DIR=${kernel.dev}/lib/modules/${kernel.modDirVersion}/build"
      "INSTALL_MOD_PATH=$(out)"
      "M=$(pwd)"
      "modules"
    ];

    # 4. Use the kernel build system to compile the modules
    buildPhase = ''
      make -C ${kernel.dev}/lib/modules/${kernel.modDirVersion}/build M=$(pwd) modules
    '';

    installPhase = ''
      make -C ${kernel.dev}/lib/modules/${kernel.modDirVersion}/build M=$(pwd) INSTALL_MOD_PATH=$out modules_install
    '';
  }) {};

in
{
  boot.extraModulePackages = [ pivccu-modules ];

  # Load the modules required for the USB stick
  boot.kernelModules = [ "cp210x" "eq3_char_loop" "plat_eq3ccu2" ];

  # Udev rules for HmIP-RFUSB
  services.udev.extraRules = ''
    # 1. FORCE BINDING: Tell cp210x to handle the HmIP-RFUSB (1b1f:c020)
    #    We use 'sh -c echo' because 'new_id' is a virtual file that tells the driver to accept new IDs.
    ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="1b1f", ATTR{idProduct}=="c020", \
      RUN+="${pkgs.kmod}/bin/modprobe cp210x", \
      RUN+="${pkgs.bash}/bin/sh -c 'echo 1b1f c020 > /sys/bus/usb-serial/drivers/cp210x/new_id'"

    # 2. CREATE SYMLINK: Once the driver binds, a ttyUSBx device appears. 
    #    We symlink it to /dev/raw-uart and set permissions.
    SUBSYSTEM=="tty", ATTRS{idVendor}=="1b1f", ATTRS{idProduct}=="c020", SYMLINK+="raw-uart", OWNER="root", GROUP="root", MODE="0666"
    
    # 3. USB PERMISSIONS: Ensure the raw USB device is also accessible
    SUBSYSTEM=="usb", ATTRS{idVendor}=="1b1f", ATTRS{idProduct}=="c020", MODE="0666"
    '';
}