{ pkgs, config, lib, ... }:
with lib;
let
  cfg = config.services.minecraft.forge;
in
{
  options.services.minecraft.forge = {
    enable = mkEnableOption "Enable Minecraft server service.";

    modpackId = mkOption {
      type = types.int;
    };

    versionId = mkOption {
      type = types.int;
    };

    modpacksChHash = mkOption {
      type = types.str;
    };

    javaPackage = mkOption {
      type = types.package;
      default = pkgs.jdk17;
    };

    serverPackage = mkOption {
      type = types.package;
      readOnly = true;
    };

    eulaAccept = mkOption {
      type = with types; bool;
      description = ''
        By changing the setting below to true you are indicating your agreement to Mojang's EULA (https://account.mojang.com/documents/minecraft_eula).
      '';
      default = false;
    };

    extraJavaArguments = mkOption {
      type = with types; listOf str;
      default = [];
    };

    extraFixup = mkOption {
      type = types.lines;
      default = "";
    };
  };

  config = mkIf cfg.enable {

    services.minecraft.forge.serverPackage =
      let
        forgeFod =
          pkgs.stdenv.mkDerivation {
            pname = "minecraft";
            version = "unknown";

            outputHashMode = "recursive";
            outputHashAlgo = "sha256";
            outputHash = cfg.modpacksChHash;

            buildInputs = with pkgs; [ unzip curl which cacert ];

            phases = [ "fetchPhase" "installPhase" "fixupPhase "];

            fetchPhase = ''
              curl https://api.modpacks.ch/public/modpack/${toString cfg.modpackId}/${toString cfg.versionId}/server/linux -o modpacks.ch # fuck creeperhost
              chmod +x modpacks.ch
            '';

            installPhase = ''
              mkdir ebin $out

              cat > ebin/java <<EOF
              #!$(which sh)

              echo "cd \$PWD && java \$@" > install-forge
              EOF
              chmod +x ebin/java
              export PATH=$PWD/ebin:$PATH

              ./modpacks.ch ${toString cfg.modpackId} ${toString cfg.versionId} --nojava --path $out --verbose
            '';

            fixupPhase = ''
              # delete useless non-reproducible data that we really don't need. A less "shotgun" cleaning is possible
              rm $out/version.json

              ${cfg.extraFixup}
            '';
          };
      in
        pkgs.stdenv.mkDerivation {
          pname = "minecraft";
          version = "unknown";

          phases = [ "installPhase" ];

          installPhase = ''
            mkdir -p $out/bin

            cp ${pkgs.writeShellScript "server.sh" ''
              export PATH=${makeBinPath (with pkgs; [ coreutils findutils bash cfg.javaPackage ])}:$PATH
              export _path=$PWD
              echo $0

              echo $rw_paths
              function linkFile()
              {
                _rw_paths=${"( " + lib.concatMapStringsSep " " (x: ''"${x}"'') [ "config" "modpack/gamemodes.json" ] + " )"}
                _ignore_paths=${"( " + lib.concatMapStringsSep " " (x: ''"${x}"'') [ "start.sh" ] + " )"}

                echo $1 | grep MrTJP

                ignore=0
                for ignore_path in ''${_ignore_paths[@]} ; do
                  if [ "''${1##ignore_path}" != "$1" ] || [ "$ignore_path" = "$1" ] ; then
                    ignore=1
                    break
                  fi
                done

                if [ -f "$1" ] || [ $ignore = 1 ] ; then
                  return
                fi
                mkdir -p "$_path/$(dirname "$1")"

                copy=0
                for rw_path in ''${_rw_paths[@]} ; do
                  if [ "''${1##$rw_path}" != "$1" ] || [ "$rw_path" = "$1" ] ; then
                    copy=1
                    break
                  fi
                done

                if [ "$copy" = 1 ] ; then
                  cp --no-preserve=mode,ownership "${forgeFod}/$1" "$_path/$1"
                else
                  ln -s "${forgeFod}/$1" "$_path/$1"
                fi
              }
              export -f linkFile

              echo $_path
              if [ "$_path" = "" ] || ! [ -d "$_path" ] ; then
                echo "invalid path"
                exit 1
              fi

              find $_path -type l -lname '/nix/store/*' -delete
              find $_path -type d -empty -delete

              find ${forgeFod} -type f -printf '%P\n' | tr '\n' '\0' | xargs -0 -I {} sh -c 'linkFile "$1"' sh {} # mkdir -p "$_path/$(dirname "$1")" ; ln -s "${forgeFod}/$1" "$_path/$1"

              ln -s ${pkgs.writeShellScript "start.sh" ''
                ${lib.getExe cfg.javaPackage} $(cat ${forgeFod}/start.sh  | grep -e "java" -e jar | sed 's/^"java" \(.*\) -jar .*$/\1/') "$@" -jar forge-*.jar
              ''} $_path/start.sh

              # [ -f $_path/install-forge ] && bash install-forge

              $_path/start.sh
            ''} $out/bin/server
          '';
        };

    init.services.minecraft-forge = {
      script = pkgs.writeShellScript "minecraft-run" ''
        set -xe

        mkdir -p /var/lib/minecraft/forge
        cd /var/lib/minecraft/forge
        echo "eula=true" > eula.txt
        ${pkgs.bash}/bin/bash -x ${cfg.serverPackage}/bin/server ${concatMapStringsSep " " (x: ''"${x}"'') cfg.extraJavaArguments}
      '';
      enabled = true;
    };

    assertions = [
      { assertion = cfg.eulaAccept;
        message = "You must accept the EULA";
      }
    ];
  };
}