Check for nixos-rebuild command triggers notification if not found

Add source argument to default notification title

src/nix_background_upgrade/nixos.py

@@ -3,13 +3,23 @@ Control upgrading NixOS configuration
 """
 
 import subprocess
+from os import getenv
+
+from .notification import create_notification
+
+NIXOS_CONFIGURATION: str = getenv("NIXOS_CONFIGURATION", "")
 
 
-def nixos_switch() -> None:
+def nixos_switch() -> int:
     """
     Switch NixOS system to new version
 
-    :returns: None
+    :returns: Error code of `sudo nixos-rebuild switch` call
     """
-    subprocess.Popen("which -a nixos-rebuild".split())
-    return
+    notification = create_notification(source="nixos_switch")
+    try:
+        subprocess.run("which -a nixos-rebuild".split()).check_returncode()
+    except subprocess.CalledProcessError as e:
+        notification.message = e
+        notification.send()
+    return 0

src/nix_background_upgrade/notification.py

@@ -1,16 +1,21 @@
 from pathlib import Path
+from typing import Optional
 
 from notifypy import Notify
 
 
-def create_notification() -> Notify:
+def create_notification(source: Optional[str] = None) -> Notify:
     """
     Create notification class
 
+    :param source: Name of originating file or function, used in default notification
+        title
+
     :returns: Notify class with custom defaults
     """
+    if source is None:
+        source = "Nix process"
     return Notify(
-        default_notification_title="Nix Background Update",
-        default_notification_message="Message from Nix process",
+        default_notification_title="Message from {}".format(source),
         default_notification_icon=Path(__file__).parent / "./nix-snowflake.png",
     )