nixos/nncp: refactor configuration merging

      wantedBy = [ "basic.target" ];

      serviceConfig.Type = "oneshot";

      script = ''

        umask u=rw

        nncpCfgDir=$(mktemp --directory nncp.XXX)

        for f in ${jsonCfgFile} ${builtins.toString config.programs.nncp.secrets}; do

          tmpdir=$(mktemp --directory nncp.XXX)

          nncp-cfgdir -cfg $f -dump $tmpdir

          find $tmpdir -size 1c -delete

          cp -a $tmpdir/* $nncpCfgDir/

          rm -rf $tmpdir

        done

        nncp-cfgdir -load $nncpCfgDir > ${nncpCfgFile}

        rm -rf $nncpCfgDir

        umask 127

        rm -f ${nncpCfgFile}

        for f in ${jsonCfgFile} ${builtins.toString config.programs.nncp.secrets}

        do

          ${lib.getExe pkgs.hjson-go} -c <"$f"

        done |${lib.getExe pkgs.jq} --slurp add >${nncpCfgFile}

        chgrp ${programCfg.group} ${nncpCfgFile}

        chmod g+r ${nncpCfgFile}

      '';

    };

  };