{ lib, stdenv, fetchurl, busybox, coreutils, jre_headless, runtimeShell
, mods ? null, modConfig ? null, defaultconfigs ? null }:

let
  name = "forge-server";
  version = "1.16.5-36.2.2";
  mirror = "https://files.minecraftforge.net/maven/net/minecraftforge/forge";
  src = fetchurl {
    url = "${mirror}/${version}/forge-${version}-installer.jar";
    # Forge doesn't seem to like newer shas
    sha1 = "e97821e5431bdcaa46e12048769922e2cdb5e2e1";
  };

  unpackCmd = "mkdir -p src; cp $curSrc src/forge-${version}-installer.jar";

  nativeBuildInputs = [ jre_headless ];

  # Somewhat evil pre-install step to run through the network
  # dependency resolution forge needs. This is also common for gradle
  # projects, so I think this is ok-ish here, though ideally I'd
  # identify all the dependencies and package them as well.
  deps = stdenv.mkDerivation {
    name = "${name}-deps";
    inherit src unpackCmd nativeBuildInputs;

    buildPhase = ''
      java -jar forge-${version}-installer.jar --installServer installation
    '';
    installPhase = ''
      mkdir -p $out

      # The installer will patch the Minecraft server jar in some
      # fashion, and include it in "libraries". This'd be fine, if the
      # patch was bit-for-bit reproducible. Sadly it is not, so we
      # defer this to the *real* package build.
      rm -r installation/libraries/net/minecraft/

      cp -r installation/* $out
    '';

    outputHashAlgo = "sha256";
    outputHashMode = "recursive";
    outputHash = "VuUGc5JnzcRhDt9aaGrU+yUrJILVdU2vzv1PxLwdAig=";
  };

in stdenv.mkDerivation rec {
  inherit name version src unpackCmd nativeBuildInputs;

  buildPhase = ''
    mkdir -p installation

    # Take the input deps and patch the Minecraft server jar into our
    # libraries to create the package.
    cp -rv ${deps}/* installation/
    chmod -R +w installation/
    java -jar forge-${version}-installer.jar --offline --installServer installation/
  '';

  installPhase = ''
    mkdir -p $out/{bin,lib/forge}

    cp -r installation/{forge-${version}.jar,libraries} $out/lib/forge/

    cat > $out/bin/forge-server << EOF
    #!${runtimeShell}
    set -eu

    # Delete any previous mods directory so that it can be updated
    ${busybox}/bin/rm -fr mods

    ${lib.optionalString (mods != null) ''
      # Copy the specified mods into the directory. Note that, sadly,
      # forge doesn't support symlinks here.
      ${busybox}/bin/mkdir -p mods
      ${busybox}/bin/cp -r '${mods}/mods/'*.jar mods
    ''}

    # Delete any previous config directories so that they can be updated
    ${busybox}/bin/rm -fr config defaultconfigs

    ${lib.optionalString (modConfig != null) ''
      # Copy the specified configs into the directory. Forge (and
      # mods) will try to write here, so we cannot symlink.
      ${busybox}/bin/mkdir -p config
      ${busybox}/bin/cp -r '${modConfig}'/* config
      ${busybox}/bin/chmod -R u+w config
    ''}

    ${lib.optionalString (defaultconfigs != null) ''
      # Copy the specified configs into the directory. Forge (and
      # mods) will try to write here, so we cannot symlink.
      ${busybox}/bin/mkdir -p defaultconfigs
      ${busybox}/bin/cp -r '${defaultconfigs}'/* defaultconfigs
      ${busybox}/bin/chmod -R u+w defaultconfigs
    ''}

    exec ${jre_headless}/bin/java \$@ -jar $out'/lib/forge/forge-${version}.jar' nogui
    EOF

    chmod +x $out/bin/forge-server
  '';

  meta = with lib; {
    description = "Forge Minecraft Server";
    homepage = "https://files.minecraftforge.net/";
    # Forge itself is open source, but this package pulls in
    # minecraft.
    license = licenses.unfreeRedistributable;
    platforms = platforms.unix;
  };
}