{ lib, stdenv, fetchurl, pkg-config, unzip, zlib, libpng, bzip2, SDL, SDL_mixer
, buildEnv, config, runtimeShell
}:

let
  # Choose your "paksets" of objects, images, text, music, etc.
  paksets = config.simutrans.paksets or "pak64 pak64.japan pak128 pak128.britain pak128.german";

  result = withPaks (
    if paksets == "*" then lib.attrValues pakSpec # taking all
      else map (name: pakSpec.${name}) (lib.splitString " " paksets)
  );

  ver1 = "121";
  ver2 = "0";
  ver3 = "";
  version  = "${ver1}.${ver2}${lib.optionalString (ver3 != "") ".${ver3}"}";
  ver_dash = "${ver1}-${ver2}${lib.optionalString (ver3 != "") "-${ver3}"}";

  binary_src = fetchurl {
    url = "mirror://sourceforge/simutrans/simutrans/${ver_dash}/simutrans-src-${ver_dash}.zip";
    sha256 = "1f463r6kr5ig0zd3mncc74k93xbjywsq3d06j5r17831jyc9bzb9";
  };


  # As of 2021/07, many of these paksets have not been updated for years, so are on old versions.
  pakSpec = lib.mapAttrs
    (pakName: attrs: mkPak (attrs // {inherit pakName;}))
  {
    pak64 = {
      srcPath = "${ver_dash}/simupak64-${ver_dash}";
      sha256 = "1k335kh8dhm1hdn5iwn3sdgnrlpk0rqxmmgqgqcwsi09cmw45m5c";
    };
    "pak64.japan" = {
      # No release for 121.0 yet!
      srcPath = "120-0/simupak64.japan-120-0-1";
      sha256 = "14swy3h4ij74bgaw7scyvmivfb5fmp21nixmhlpk3mav3wr3167i";
    };

    pak128 = {
      srcPath = "pak128%20for%20ST%20120.4.1%20%282.8.1%2C%20priority%20signals%20%2B%20bugfix%29/pak128";
      sha256 = "0z01y7r0rz7q79vr17bbnkgcbjjrimphy1dwb1pgbiv4klz7j5xw";
    };
    "pak128.britain" = {
      srcPath = "pak128.Britain%20for%20120-1/pak128.Britain.1.18-120-3";
      sha256 = "1kyb0s54kysvdr0zdln9106yx75d71j4lbw3v87k3i440cj3r1d3";
    };
    "pak128.cs" = { # note: it needs pak128 to work
      url = "mirror://sourceforge/simutrans/Pak128.CS/pak128.cz_v.0.2.1.zip";
      sha256 = "008d8x1s0vxsq78rkczlnf57pv1n5hi1v5nbd1l5w3yls7lk11sc";
    };
    "pak128.german" = {
      url = "mirror://sourceforge/simutrans/PAK128.german/"
        + "pak128.german_1.2_for_ST_121.0/PAK128.german_1.2_for_ST_121-0.zip";
      sha256 = "1cv1rzl1a3i5dvk476zq094wawk9hhdh2f0y4xrdny5gn17mb2xi";
    };

    /* This release contains accented filenames that prevent unzipping.
    "pak192.comic" = {
      srcPath = "pak192comic%20for%20${ver2_dash}/pak192comic-0.4-${ver2_dash}up";
      sha256 = throw "";
    };
    */
  };


  mkPak = {
    sha256, pakName, srcPath ? null
    , url ? "mirror://sourceforge/simutrans/${pakName}/${srcPath}.zip"
  }:
    stdenv.mkDerivation {
      name = "simutrans-${pakName}";
      dontUnpack = true;
      preferLocalBuild = true;
      installPhase = let src = fetchurl { inherit url sha256; };
      in ''
        mkdir -p "$out/share/simutrans/${pakName}"
        cd "$out/share/simutrans/${pakName}"
        "${unzip}/bin/unzip" "${src}"
        chmod -R +w . # some zipfiles need that

        set +o pipefail # no idea why it's needed
        toStrip=`find . -iname '*.pak' | head -n 1 | sed 's|\./\(.*\)/[^/]*$|\1|'`
        echo "Detected path '$toStrip' to strip"
        mv ./"$toStrip"/* .
        rm -f "$toStrip/.directory" #pak128.german had this
        rmdir -p "$toStrip"
      '';
    };

  /* The binaries need all data in one directory; the default is directory
      of the executable, and another option is the current directory :-/ */
  withPaks = paks: buildEnv {
    inherit (binaries) name;
    paths = [binaries] ++ paks;
    postBuild = ''
      rm "$out/bin" && mkdir "$out/bin"
      cat > "$out/bin/simutrans" <<EOF
      #!${runtimeShell}
      cd "$out"/share/simutrans
      exec "${binaries}/bin/simutrans" -use_workdir "\$@"
      EOF
      chmod +x "$out/bin/simutrans"
    '';

    passthru.meta = binaries.meta // { hydraPlatforms = []; };
    passthru.binaries = binaries;
  };

  binaries = stdenv.mkDerivation {
    pname = "simutrans";
    inherit version;

    src = binary_src;

    sourceRoot = ".";

    nativeBuildInputs = [ pkg-config unzip ];
    buildInputs = [ zlib libpng bzip2 SDL SDL_mixer ];

    configurePhase = let
      # Configuration as per the readme.txt and config.template
      platform =
        if stdenv.isLinux then "linux" else
        if stdenv.isDarwin then "mac" else throw "add your platform";
      config = ''
        BACKEND = mixer_sdl
        COLOUR_DEPTH = 16
        OSTYPE = ${platform}
        VERBOSE = 1
      '';
      #TODO: MULTI_THREAD = 1 is "highly recommended",
      # but it's roughly doubling CPU usage for me
    in ''
      echo "${config}" > config.default

      # Use ~/.simutrans instead of ~/simutrans
      substituteInPlace simsys.cc --replace '%s/simutrans' '%s/.simutrans'

      # use -O2 optimization (defaults are -O or -O3)
      sed -i -e '/CFLAGS += -O/d' Makefile
      export CFLAGS+=-O2
    '';

    enableParallelBuilding = true;

    installPhase = ''
      mkdir -p $out/share/
      mv simutrans $out/share/

      mkdir -p $out/bin/
      mv build/default/sim $out/bin/simutrans
    '';

    meta = {
      description = "Simulation game in which the player strives to run a successful transport system";
      mainProgram = "simutrans";
      longDescription = ''
        Simutrans is a cross-platform simulation game in which the
        player strives to run a successful transport system by
        transporting goods, passengers, and mail between
        places. Simutrans is an open source remake of Transport Tycoon.
      '';

      homepage = "http://www.simutrans.com/";
      license = with lib.licenses; [ artistic1 gpl1Plus ];
      maintainers = [ ];
      platforms = lib.platforms.linux; # TODO: ++ darwin;
    };
  };

in result