reboot-required.nix

{ config, pkgs, ... }:
{
  systemd.timers."reboot-required-check" = {
    wantedBy = [ "timers.target" ];
    timerConfig = {
      # start at boot
      OnBootSec = "0m";
      # check every hour
      OnUnitActiveSec = "1h";
      Unit = "reboot-required-check.service";
    };
  };

  systemd.services."reboot-required-check" = {
    script = ''
      #!/usr/bin/env bash

      # compare current system with booted sysetm to determine if a reboot is required
      if [[ "$(readlink /run/booted-system/{initrd,kernel,kernel-modules})" == "$(readlink /run/current-system/{initrd,kernel,kernel-modules})" ]]; then
        # check if the '/var/run/reboot-required' file exists and if it does, remove it
        if [[ -f /var/run/reboot-required ]]; then
          rm /var/run/reboot-required || { echo "Failed to remove /var/run/reboot-required"; exit 1; }
        fi
      else
        echo "reboot required"
        touch /var/run/reboot-required || { echo "Failed to create /var/run/reboot-required"; exit 1; }
      fi
    '';
    serviceConfig = {
      Type = "oneshot";
      User = "root";
    };
  };
}