Add notification for failed backups

backup.nix

@@ -1,6 +1,27 @@
 { pkgs, config, ... }:
 {
-  environment.systemPackages = [pkgs.restic];
+  environment.systemPackages = with pkgs; [
+    restic
+    libnotify
+  ];
+
+  systemd.services = {
+    notify-backup-b2-failed = {
+      description = "Notify on failed backup to B2";
+      serviceConfig = {
+        Type = "oneshot";
+        User = "nettika";
+      };
+      environment = {
+        DBUS_SESSION_BUS_ADDRESS = "unix:path=/run/user/1000/bus";
+      };
+      path = [ pkgs.libnotify ];
+      script = "notify-send -u critical \"Backup to B2 failed\" \"$(journalctl -u restic-backups-b2 -n 5 -o cat)\"";
+    };
+    restic-backups-b2 = {
+      onFailure = ["notify-backup-b2-failed.service"];
+    };
+  };
 
   services.restic.backups = {
     b2 = {