nix-config/_/nixos/_mixins/global/auto-upgrade.nix

{ config, inputs, pkgs, lib, ... }:
let
  inherit (config.networking) hostName;
  # Only enable auto upgrade if current config came from a clean tree
  # This avoids accidental auto-upgrades when working locally.
  isClean = inputs.self ? rev;
in
{
  system.autoUpgrade = {
    enable = isClean;
    dates = "hourly";
    flags = [
      "--refresh"
    ];
    flake = "git://github.com/gburd/nix-config?ref=release-${hostName}";
  };

  # Only run if current config (self) is older than the new one.
  systemd.services.nixos-upgrade = lib.mkIf config.system.autoUpgrade.enable {
    serviceConfig.ExecCondition = lib.getExe (
      pkgs.writeShellScriptBin "check-date" ''
        lastModified() {
          nix flake metadata "$1" --refresh --json | ${lib.getExe pkgs.jq} '.lastModified'
        }
        test "$(lastModified "${config.system.autoUpgrade.flake}")"  -gt "$(lastModified "self")"
      ''
    );
  };
}