{ system ? builtins.currentSystem, pkgs ? import <nixpkgs> { inherit system; }
, ... }:

let
  retroPlatforms = {
    m68k = {
      system = "m68k-macos";
      config = "m68k-apple-macos";
      libc = "retro68";
      parsed = {
        cpu = {
          name = "m68k";
          bits = 32;
          significantByte = { name = "bigEndian"; };
          family = "m68k";
        };
        kernel = {
          name = "macos";
          execFormat = { name = "unknown"; };
        };
      };
      bfdEmulation = "m68k";
      isStatic = true;

      retro68GccConfig = [ "--with-arch=m68k" "--with-cpu=m68000" ];
      retro68 = true;
      cmakeSystemName = "Retro68";
    };
    powerpc = {
      system = "powerpc-macos";
      config = "powerpc-apple-macos";
      libc = "retro68";
      parsed = {
        cpu = {
          name = "powerpc";
          bits = 32;
          significantByte = { name = "bigEndian"; };
          family = "power";
        };
        kernel = {
          name = "macos";
          execFormat = { name = "unknown"; };
        };
      };

      isStatic = true;
      retro68BinutilsConfig = [ "--disable-plugins" ];
      retro68GccConfig = [ "--disable-lto" ];
      retro68 = true;
      cmakeSystemName = "RetroPPC";
    };
    carbon = {
      system = "powerpc-carbon";
      config = "powerpc-apple-carbon";
      libc = "retro68";
      parsed = {
        cpu = {
          name = "powerpc";
          bits = 32;
          significantByte = { name = "bigEndian"; };
          family = "power";
        };
        kernel = {
          name = "carbon";
          execFormat = { name = "unknown"; };
        };
      };
      isStatic = true;
      retro68BinutilsConfig = [ "--disable-plugins" ];
      retro68GccConfig = [ "--disable-lto" ];
      retro68 = true;
      cmakeSystemName = "RetroCarbon";
    };

    isStatic = true;
    retro68BinutilsConfig = [ "--disable-plugins" ];
    retro68GccConfig = [ "--disable-lto" ];
    retro68 = true;
  };

  # A Nixpkgs overlay.
  overlay = pkgs: prev:
    {
      retro68 = {
        platforms = retroPlatforms;

        # ----------- Native Tools -------------
        # hfsutils -- Utilities for manipulating HFS volumes & disk images.
        hfsutils = with pkgs;
          stdenv.mkDerivation {
            name = "retro68.hfsutils";
            srcs = ./hfsutils;

            preConfigure = ''
              mkdir -p $out/bin
              mkdir -p $out/lib
              mkdir -p $out/include
              mkdir -p $out/share/man/man1
            '';
            configureFlags = [ "--mandir=$(out)/share/man" "--enable-devlibs" ];
          };

        # tools -- native tools that are part of Retro68
        tools = with pkgs;
          stdenv.mkDerivation {
            name = "retro68.tools";
            src = nix-gitignore.gitignoreSource [
              "/*"
              "!/CMakeLists.txt"
              "!/libelf" # should perhaps use nixpkg's libelf instead?
              "!/cmake"
              "!/LaunchAPPL"
              "!/libretro"
              "!/PEFTools"
              "!/ResourceFiles"
              "!/Rez"
              "!/Elf2Mac"
              "!/ConvertObj"
              "!/ConvertDiskImage"
            ] ./.;

            nativeBuildInputs = [ cmake bison flex ];
            buildInputs = [ boost zlib retro68.hfsutils ];
          };

      } // prev.lib.optionalAttrs (prev.targetPlatform ? retro68) {

        # ----------- Binutils & GCC -------------

        # binutils_unwrapped -- binutils, without any wrappers
        binutils_unwrapped = with pkgs;
          stdenv.mkDerivation rec {
            name = "retro68.binutils_unwrapped";
            src = ./binutils;

            configureFlags =
              [ "--target=${stdenv.targetPlatform.config}" "--disable-doc" ]
              ++ stdenv.targetPlatform.retro68BinutilsConfig or [ ];
            enableParallelBuilding = true;

            postInstall = let
              ld = "$out/bin/${stdenv.targetPlatform.config}-ld";
              ld_real = "$out/bin/${stdenv.targetPlatform.config}-ld.real";

            in ''
              mv ${ld} ${ld_real}

              echo "#!${stdenv.shell}" > ${ld}
              echo "exec \$'' + ''
                {RETRO68_LD_WRAPPER_${stdenv.targetPlatform.cmakeSystemName}-${ld_real}} \"\$@\"" >> ${ld}
                                chmod +x ${ld}

                                rm $out/${stdenv.targetPlatform.config}/bin/ld
                                ln -s ${ld} $out/${stdenv.targetPlatform.config}/bin/ld
                              '';
          };

        # gcc -- gcc, without any wrappers
        gcc_unwrapped = with pkgs;
          stdenv.mkDerivation rec {
            name = "retro68.gcc_unwrapped";
            src = ./gcc;
            buildInputs = [ retro68.binutils_unwrapped gmp mpfr libmpc ];
            configureFlags = [
              "--target=${stdenv.targetPlatform.config}"
              "--enable-languages=c,c++"
              "--disable-libssp"
              "MAKEINFO=missing"
            ] ++ stdenv.targetPlatform.retro68GccConfig or [ ];
            hardeningDisable = [ "format" ];
            enableParallelBuilding = true;

            # nix does in-source builds by default, and something breaks
            buildCommand = ''
              mkdir -p $out/${stdenv.targetPlatform.config}/bin
              ln -s ${retro68.binutils_unwrapped}/${stdenv.targetPlatform.config}/bin/* $out/${stdenv.targetPlatform.config}/bin/

              export target_configargs="--disable-nls --enable-libstdcxx-dual-abi=no --disable-libstdcxx-verbose"
              $src/configure ${builtins.toString configureFlags} --prefix=$out
              make -j$NIX_BUILD_CORES
              make install
            '';
          };

      } // prev.lib.optionalAttrs (prev.hostPlatform ? retro68) {

        setup_hook = let
          systemName = pkgs.targetPlatform.cmakeSystemName;
          toolchain = pkgs.writeTextFile {
            name = "retro68.cmake-toolchain";
            text = ''
              set(CMAKE_SYSTEM_NAME ${systemName})
              set(CMAKE_SYSTEM_VERSION 1)
              set(CMAKE_CROSSCOMPILING TRUE)

              set(REZ "${pkgs.buildPackages.retro68.tools}/bin/Rez" )
              set(REZ_TEMPLATES_PATH ${pkgs.retro68.libretro}/RIncludes)

              set(MAKE_PEF "${pkgs.buildPackages.retro68.tools}/bin/MakePEF" )

              include(${./cmake/add_application.cmake})
            '';
          };
          hook = pkgs.writeTextFile {
            name = "retro68.setup_hook";
            text = ''
              export CMAKE_TOOLCHAIN_FILE=${toolchain}

              retro68_addRIncludes() {
                case $depHostOffset in
                    -1) local role='BUILD_' ;;
                    0)  local role="" ;;
                    1)  local role='TARGET_' ;;
                    *)  echo "retro68_addRIncludes: Error: Cannot be used with $depHostOffset-offset deps" >2;
                        return 1 ;;
                esac

                if [[ -d "$1/RIncludes" ]]; then
                    export REZ_INCLUDE_PATH+=":$1/RIncludes"
                fi
              }

              addEnvHooks "$targetOffset" retro68_addRIncludes

            '' + (pkgs.lib.optionalString (systemName == "Retro68") ''
              export RETRO68_LD_WRAPPER_Retro68="${pkgs.buildPackages.retro68.tools}/bin/Elf2Mac"
              export RETRO68_REAL_LD="${pkgs.buildPackages.retro68.binutils_unwrapped}/bin/m68k-apple-macos-ld.real"
            '');
          };
        in pkgs.makeSetupHook { } hook;

        # ----------- Retro68 core libraries -------------

        # multiversal -- multiversal interfaces
        multiversal = with pkgs;
          (stdenv.override {
            cc = stdenv.cc.override { extraPackages = [ ]; };
          }).mkDerivation {
            name = "retro68.multiversal";
            src = ./multiversal;
            nativeBuildInputs = [ buildPackages.ruby ];
            buildCommand = ''
              echo $src
              build=`pwd`
              (cd $src && ruby make-multiverse.rb -G CIncludes -o "$build")
              mkdir $out
              cp -r CIncludes $out/include
              cp -r RIncludes $out/
            '' + (if stdenv.targetPlatform.system == "m68k-macos" then ''
              cp -r lib68k $out/lib
            '' else
              "");
          };

        import_libraries = with pkgs;
          if stdenvNoCC.targetPlatform != retroPlatforms.m68k then
            stdenvNoCC.mkDerivation {
              name = "retro68.import_libraries";
              src = ./ImportLibraries;
              buildCommand = ''
                mkdir -p $out/lib
                cp $src/*.a $out/lib/
              '';
            }
          else
            null;

        libretro = with pkgs;
          let
            systemName = pkgs.targetPlatform.cmakeSystemName;
            toolchain = pkgs.writeTextFile {
              name = "retro68-cmake-toolchain-bootstrap";
              text = ''
                set(CMAKE_SYSTEM_NAME ${systemName})
                set(CMAKE_SYSTEM_VERSION 1)
                set(CMAKE_CROSSCOMPILING TRUE)
              '';
            };
          in (pkgs.stdenv.override {
            cc = stdenv.cc.override { extraPackages = [ ]; };
          }).mkDerivation {
            name = "libretro";
            src = ./libretro;

            nativeBuildInputs = [ buildPackages.cmake ];
            buildInputs = [ retro68.multiversal ];

            buildCommand = ''
              echo "Build command."
              cmake $src \
                      -DCMAKE_INSTALL_PREFIX=$out \
                      -DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY \
                      -DCMAKE_BUILD_TYPE=Release \
                      -DCMAKE_TOOLCHAIN_FILE=${toolchain}
              cmake --build .
              cmake --build . --target install
            '';
          };

          console = with pkgs;
            stdenv.mkDerivation {
              name = "retro68.console";
              src = ./Console;

              nativeBuildInputs = [ buildPackages.cmake ];
            };
      };
    } // prev.lib.optionalAttrs (prev.targetPlatform ? retro68) {

      # ----------- Binutils & GCC wrapped for nixpkgs -------------

      # binutils -- binutils with the wrappers provided by nixpkgs 
      binutils =
        pkgs.wrapBintoolsWith { bintools = pkgs.retro68.binutils_unwrapped; };

      # gcc -- gcc with the wrappers provided by nixpkgs
      gcc = pkgs.wrapCCWith {
        cc = pkgs.retro68.gcc_unwrapped;

        # don't allow nix to add options for hardening
        extraBuildCommands = ''
          echo "" > $out/nix-support/add-hardening.sh
        '';

        extraPackages = with pkgs.targetPackages.retro68; [
          multiversal
          import_libraries
          libretro
          setup_hook
        ];
      };

      # no separate libc package for now
      libcCrossChooser = name:
        if name == "retro68" then null else prev.libcCrossChooser name;

    };

  pkgs = import <nixpkgs> {
    inherit system;
    overlays = [ overlay ];
  };

  crossPkgs = pkgs.lib.mapAttrs (name: plat:
    import <nixpkgs> {
      inherit system;
      overlays = [ overlay ];
      crossSystem = plat;
      config = { allowUnsupportedSystem = true; };
    }) retroPlatforms;

  shell = pkgs.lib.mapAttrs (name: cross:
    cross.mkShell {
      nativeBuildInputs = with pkgs; [
        retro68.hfsutils
        retro68.tools
        cmake
        gnumake
      ];
      buildInputs = [ cross.retro68.console ];
    } // cross) crossPkgs;

in shell.m68k // shell // { inherit overlay; }