{ lib
, pkgs
, callPackage
, writeShellScriptBin
, writeText
, linuxPackagesFor
, _4KBuild ? false
, withRust ? false
, kernelPatches ? [ ]
}:

let
  # TODO: use a pure nix regex parser instead of an IFD, and remove this workaround
  localPkgs = if builtins ? currentSystem
    then import (pkgs.path) {
      crossSystem.system = builtins.currentSystem;
      localSystem.system = builtins.currentSystem;
    }
    else pkgs;

  inherit (localPkgs) runCommand;

  parseExtraConfig = cfg: let
    lines = builtins.filter (s: s != "") (lib.strings.splitString "\n" cfg);
    perLine = line: let
      kv = lib.strings.splitString " " line;
    in assert (builtins.length kv == 2);
       "CONFIG_${builtins.elemAt kv 0}=${builtins.elemAt kv 1}";
    in lib.strings.concatMapStringsSep "\n" perLine lines;

  readConfig = configfile: import (runCommand "config.nix" { } ''
    echo "{ } // " > "$out"
    while IFS='=' read key val; do
      [ "x''${key#CONFIG_}" != "x$key" ] || continue
      no_firstquote="''${val#\"}";
      echo '{  "'"$key"'" = "'"''${no_firstquote%\"}"'"; } //' >> "$out"
    done < "${configfile}"
    echo "{ }" >> $out
  '').outPath;

  linux-asahi-pkg = { stdenv, lib, fetchFromGitHub, fetchpatch, linuxKernel,
      rustPlatform, rustfmt, rust-bindgen, ... } @ args:
    let
      configfile = if kernelPatches == [ ] then ./config else
        writeText "config" ''
          ${builtins.readFile ./config}

          # Patches
          ${lib.strings.concatMapStringsSep "\n" ({extraConfig ? "", ...}: parseExtraConfig extraConfig) kernelPatches}
        '';

      _kernelPatches = kernelPatches;
    in
    (linuxKernel.manualConfig rec {
      inherit stdenv lib;

      version = "6.1.0-asahi";
      modDirVersion = version;

      src = fetchFromGitHub {
        # tracking: https://github.com/AsahiLinux/PKGBUILDs/blob/stable/linux-asahi/PKGBUILD
        owner = "AsahiLinux";
        repo = "linux";
        rev = "asahi-6.1-2";
        hash = "sha256-grQytmYoAlPxRI8mYQjZFduD3BH7PA7rz1hyInJb4JA=";
      };

      kernelPatches = [
      ] ++ lib.optionals _4KBuild [
        # thanks to Sven Peter
        # https://lore.kernel.org/linux-iommu/20211019163737.46269-1-sven@svenpeter.dev/
        { name = "sven-iommu-4k";
          patch = ./sven-iommu-4k.patch;
        }
      ] ++ lib.optionals (!_4KBuild) [
        # patch the kernel to set the default size to 16k instead of modifying
        # the config so we don't need to convert our config to the nixos
        # infrastructure or patch it and thus introduce a dependency on the host
        # system architecture
        { name = "default-pagesize-16k";
          patch = ./default-pagesize-16k.patch;
        }
      ] ++ _kernelPatches;

      inherit configfile;
      config = readConfig configfile;

      extraMeta.branch = "6.1";
    } // (args.argsOverride or {})).overrideAttrs (old: if withRust then {
      nativeBuildInputs = (old.nativeBuildInputs or []) ++ [
        rust-bindgen
        rustfmt
        # rustc 1.66.x has problems relating to the sad old aarch64 GCC9.
        # we need it to pass -lgcc to gcc through the nix machinery but only when rustc
        # is running, so we give the kernel build a rustc that wraps the real rustc
        # while setting the appropriate environment variable during its execution.
        # https://github.com/NixOS/nixpkgs/pull/209113
        (writeShellScriptBin "rustc" ''
          NIX_LDFLAGS=-lgcc ${rustPlatform.rust.rustc}/bin/rustc "$@"
        '')
      ];
      RUST_LIB_SRC = rustPlatform.rustLibSrc;

      preConfigure = ''
        # Fixes for Rust 1.66.x
        sed -i -e 's/rustc_allocator_nounwind/rustc_nounwind/g' rust/alloc/alloc.rs
        sed -i -e 's/const Unpin/Unpin/' rust/alloc/boxed.rs
        sed -i -e '/^pub unsafe trait RawDeviceId/i #[const_trait]' rust/kernel/driver.rs

        # Fixes for rust-bindgen 0.63.0
        sed -i -e 's/blacklist/blocklist/g' rust/Makefile
        sed -i -e 's/whitelist/allowlist/g' rust/Makefile
      '';
    } else {});

  linux-asahi = (callPackage linux-asahi-pkg { });
in lib.recurseIntoAttrs (linuxPackagesFor linux-asahi)