{ appleDerivation, lib, bootstrap_cmds, bison, flex
, gnum4, unifdef, perl, python3
, headersOnly ? true }:

appleDerivation ({
  nativeBuildInputs = [ bootstrap_cmds bison flex gnum4 unifdef perl python3 ];

  patches = [ ./python3.patch ];

  postPatch = ''
    substituteInPlace Makefile \
      --replace "/bin/" "" \
      --replace "MAKEJOBS := " '# MAKEJOBS := '

    substituteInPlace makedefs/MakeInc.cmd \
      --replace "/usr/bin/" "" \
      --replace "/bin/" "" \
      --replace "-Werror " ""

    substituteInPlace makedefs/MakeInc.def \
      --replace "-c -S -m" "-c -m"

    substituteInPlace makedefs/MakeInc.top \
      --replace "MEMORY_SIZE := " 'MEMORY_SIZE := 1073741824 # '

    substituteInPlace libkern/kxld/Makefile \
      --replace "-Werror " ""

    substituteInPlace SETUP/kextsymboltool/Makefile \
      --replace "-lstdc++" "-lc++"

    substituteInPlace libsyscall/xcodescripts/mach_install_mig.sh \
      --replace "/usr/include" "/include" \
      --replace "/usr/local/include" "/include" \
      --replace 'MIG=`' "# " \
      --replace 'MIGCC=`' "# " \
      --replace " -o 0" "" \
      --replace '$SRC/$mig' '-I$DSTROOT/include $SRC/$mig' \
      --replace '$SRC/servers/netname.defs' '-I$DSTROOT/include $SRC/servers/netname.defs' \
      --replace '$BUILT_PRODUCTS_DIR/mig_hdr' '$BUILT_PRODUCTS_DIR'

    patchShebangs .
  '';

  PLATFORM = "MacOSX";
  SDKVERSION = "10.11";
  CC = "cc";
  CXX = "c++";
  MIG = "mig";
  MIGCOM = "migcom";
  STRIP = "strip";
  NM = "nm";
  UNIFDEF = "unifdef";
  DSYMUTIL = "dsymutil";
  HOST_OS_VERSION = "10.10";
  HOST_CC = "cc";
  HOST_FLEX = "flex";
  HOST_BISON = "bison";
  HOST_GM4 = "m4";
  MIGCC = "cc";
  ARCHS = "x86_64";

  NIX_CFLAGS_COMPILE = "-Wno-error";

  preBuild = ''
    # This is a bit of a hack...
    mkdir -p sdk/usr/local/libexec

    cat > sdk/usr/local/libexec/availability.pl <<EOF
      #!$SHELL
      if [ "\$1" == "--macosx" ]; then
        echo 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11
      elif [ "\$1" == "--ios" ]; then
        echo 2.0 2.1 2.2 3.0 3.1 3.2 4.0 4.1 4.2 4.3 5.0 5.1 6.0 6.1 7.0 8.0 9.0
      fi
    EOF
    chmod +x sdk/usr/local/libexec/availability.pl

    export SDKROOT_RESOLVED=$PWD/sdk
    export HOST_SDKROOT_RESOLVED=$PWD/sdk

    export BUILT_PRODUCTS_DIR=.
    export DSTROOT=$out
  '';

  buildFlags = lib.optional headersOnly "exporthdrs";
  installTargets = lib.optional headersOnly "installhdrs";

  postInstall = lib.optionalString headersOnly ''
    mv $out/usr/include $out

    (cd BUILD/obj/EXPORT_HDRS && find -type f -exec install -D \{} $out/include/\{} \;)

    # TODO: figure out why I need to do this
    cp libsyscall/wrappers/*.h $out/include
    install -D libsyscall/os/tsd.h $out/include/os/tsd.h
    cp EXTERNAL_HEADERS/AssertMacros.h $out/include
    cp EXTERNAL_HEADERS/Availability*.h $out/System/Library/Frameworks/Kernel.framework/Versions/A/Headers/
    cp -r EXTERNAL_HEADERS/corecrypto $out/include

    # Build the mach headers we crave
    export SRCROOT=$PWD/libsyscall
    export DERIVED_SOURCES_DIR=$out/include
    export SDKROOT=$out
    export OBJROOT=$PWD
    export BUILT_PRODUCTS_DIR=$out
    libsyscall/xcodescripts/mach_install_mig.sh

    # Get rid of the System prefix
    mv $out/System/* $out/
    rmdir $out/System

    # TODO: do I need this?
    mv $out/internal_hdr/include/mach/*.h $out/include/mach

    # Get rid of some junk lying around
    rm -rf $out/internal_hdr $out/usr $out/local

    # Add some symlinks
    ln -s $out/Library/Frameworks/System.framework/Versions/B \
          $out/Library/Frameworks/System.framework/Versions/Current
    ln -s $out/Library/Frameworks/System.framework/Versions/Current/PrivateHeaders \
          $out/Library/Frameworks/System.framework/Headers

    # IOKit (and possibly the others) is incomplete,
    # so let's not make it visible from here...
    mkdir $out/Library/PrivateFrameworks
    mv $out/Library/Frameworks/IOKit.framework $out/Library/PrivateFrameworks
  '';
} // lib.optionalAttrs headersOnly {
  HOST_CODESIGN = "echo";
  HOST_CODESIGN_ALLOCATE = "echo";
  LIPO = "echo";
  LIBTOOL = "echo";
  CTFCONVERT = "echo";
  CTFMERGE = "echo";
  CTFINSERT = "echo";
  NMEDIT = "echo";
})