restructure system configuration

system/base/auto-upgrade.nix

@@ -0,0 +1,31 @@
+{ config, inputs, pkgs, lib, ... }:
+
+let
+  inherit (config.networking) hostName;
+  isClean = inputs.self ? rev;
+in
+{
+  system.autoUpgrade = {
+    enable = isClean;
+    dates = "hourly";
+    flags = [
+      "--refresh"
+    ];
+    flake = "github:ooks-io/nix#${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")"
+      ''
+    );
+  };
+}
+
+