{
  cfg,
  nixos-rebuild,
  date,
  realpath,
  stat,
  cut,
  head,
  grep,
  grub-reboot,
  shutdown,
  bootctl,
  systemd-analyze,
  upgradeFlag,
  units,
  jq,
  hostname,
  ...
}:
''
do_update() {
        hostname=$(${hostname})
        new_system=$(nix build --refresh --no-link --print-out-paths "${cfg.flake}#nixosConfigurations.''${hostname}.config.system.build.toplevel")
        
        last_flake_update_time() {
                nix flake metadata --refresh --json "$1" | ${jq} .lastModified
        }
        
        updated_since_reboot() {
                [[ $(${stat} -c %Y /run/current-system) -gt $(($(${date} +%s) - $(${cut} -d. -f1 /proc/uptime) + $(${units} --compact --one-line "ceil($(${units} --compact --one-line "$(${systemd-analyze} time | head -n 1 | ${grep} -Eo "\S+\s+$")" seconds))"))) ]]
        }
        
        boot_system_path() {
                bpath=""
                btime=0
                for f in /nix/var/nix/profiles/*
                do
                        if [[ -z $bpath ]] || [[ $btime -lt $(${stat} -c %Y $f) ]]
                        then
                                bpath=$f
                                btime=$(${stat} -c %Y $f)
                        fi
                done
                if [[ -d "/nix/var/nix/profiles/system-profiles/" ]] && [[ -n "$(ls -A /nix/var/nix/profiles/system-profiles/)" ]]
                then
                        for f in /nix/var/nix/profiles/system-profiles/*
                        do
                                if [[ -z $bpath ]] || [[ $btime -lt $(${stat} -c %Y $f) ]]
                                then
                                        bpath=$f
                                        btime=$(${stat} -c %Y $f)
                                fi
                        done
                fi
                echo "$bpath"
        }
        
        last_update_time() {
                rpath=$(${realpath} /run/current-system)
                rtime=$(${stat} -c %Y /run/current-system)
                boot_system=$(boot_system_path)
                bpath=$(${realpath} "$boot_system")
                btime=$(${stat} -c %Y "$boot_system")
                if [[ "''${rpath}" == "''${bpath}" ]]
                then
                        if ! updated_since_reboot
                        then
                                echo $btime
                                return
                        fi
                fi
                if [[ $rtime -gt $btime ]]
                then
                        echo $rtime
                else
                        echo $btime
                fi
        }
        
        latest_system=$(boot_system_path)
        
        
        if [[ "$(${realpath} /run/booted-system)" == "$(${realpath} /run/current-system)" ]] && [[ "$(${realpath} /run/booted-system)" == "$(${realpath} "$latest_system")" ]]
        then
                if [[ -f /boot/grub/grub.cfg ]]
                then
                        if [[ $(($(${date} +%s) - $(${cut} -d. -f1 /proc/uptime))) -gt $(${stat} -c %Y /boot/grub/grub.cfg) ]]
                        then
                                echo "persisting boot system"
                                "$(${realpath} /run/booted-system)/bin/switch-to-configuration" "boot"
                        fi
                fi
        fi
        
        if [[ "$new_system" == "$(${realpath} /run/current-system)" ]] && [[ "$new_system" == "$(${realpath} "$latest_system")" ]]
        then
                echo "system is up-to-date"
                exit 0
        fi
        
        system_update_time=$(last_update_time)
        flake_update_time=$(last_flake_update_time "${cfg.flake}")
        
        echo "last system update: $(${date} -d @"$system_update_time")"
        echo "last flake update: $(${date} -d @"$flake_update_time")"
        
        if [[ -z "$1" ]] && [[ "$system_update_time" -gt "$flake_update_time" ]]
        then
                echo ""
                echo "System is newer than remote!"
                echo "This happens if the system was updated manually or a system update failed."
                echo "Skipping system update to prevent potential downgrade!"
                exit 0
        fi
        
        echo "Updating system ..."
        
        system_info_booted="$(${realpath} /run/booted-system/{initrd,kernel,kernel-modules})"                                           
        system_info_built="$(${realpath} "''${new_system}"/{initrd,kernel,kernel-modules})"                                  
        
        echo $system_info_booted
        echo $system_info_built
        
        current_time="$(${date} +%H:%M)"
        
        lower=${cfg.rebootWindow.lower}
        upper=${cfg.rebootWindow.upper}
        
        if [[ "''${lower}" < "''${upper}" ]]; then
          if [[ "''${current_time}" > "''${lower}" ]] && \
             [[ "''${current_time}" < "''${upper}" ]]; then
            do_reboot="true"
          else
            do_reboot="false"
          fi
        else
          # lower > upper, so we are crossing midnight (e.g. lower=23h, upper=6h)
          # we want to reboot if cur > 23h or cur < 6h
          if [[ "''${current_time}" < "''${upper}" ]] || \
             [[ "''${current_time}" > "''${lower}" ]]; then
            do_reboot="true"
          else
            do_reboot="false"
          fi
        fi
        
        if [[ "$system_info_booted" != "$system_info_built" ]]
        then
            echo "Updating system requires reboot!"
            if [ "''${do_reboot}" != true ]
            then
                    echo "Outside of configured reboot window, skipping update."
                    exit 0
            fi
        
            echo nix-env --profile /nix/var/nix/profiles/system --set "$new_system"
            if [[ -f /boot/grub/grub.cfg ]]
            then
                    echo "bootloader 'GRUB' detected, configuring test-boot into new system"
                    "''${latest_system}/bin/switch-to-configuration" "boot"
                    ${grub-reboot} "NixOS - All configurations>0"
                    #${grub-reboot} "NixOS - Profile '$PROFILE_NAME'>0"
            elif ${bootctl} list 2>&1 | ${grep} -v "No boot loader entries found." > /dev/null
            then
                    echo "bootloader 'systemd-boot' detected, configuring oneshot-boot into new system"
                    # TODO
                    exit -1
            else
                    echo "test-boot not supported. persisting new boot system"
                    "''${new_system}/bin/switch-to-configuration" "boot"
            fi
            ${shutdown} -r +1
        else
            nix-env --profile /nix/var/nix/profiles/system --set "$new_system"
            if ! "''${new_system}/bin/switch-to-configuration" "test"
            then
                    echo "testing new configuration failed!"
                    echo "system was automatically rolled back to old configuration."
                    exit 1
            fi
            "''${new_system}/bin/switch-to-configuration" "boot"
        fi
        
        if [[ "$(last_flake_update_time "${cfg.flake}")" -gt "$flake_update_time" ]]
	then
	    echo "flake was update after last update."
	    do_update force
	fi
}
''