clan: add dynamic completion function for backup providers

pkgs/clan-cli/clan_cli/completions.py

@@ -118,6 +118,49 @@ def complete_services_for_machine(
     return services_dict
 
 
+def complete_backup_providers_for_machine(
+    prefix: str, parsed_args: argparse.Namespace, **kwargs: Any
+) -> Iterable[str]:
+    """
+    Provides completion functionality for machine backup providers.
+    """
+    services: list[str] = []
+    # TODO: consolidate, if multiple machines are used
+    machines: list[str] = parsed_args.machines
+
+    def run_cmd() -> None:
+        try:
+            if (clan_dir_result := clan_dir(None)) is not None:
+                flake = clan_dir_result
+            else:
+                flake = "."
+            services_result = json.loads(
+                run(
+                    nix_eval(
+                        flags=[
+                            f"{flake}#nixosConfigurations.{machines[0]}.config.clanCore.backups.providers",
+                            "--apply",
+                            "builtins.attrNames",
+                        ],
+                    ),
+                ).stdout.strip()
+            )
+
+            services.extend(services_result)
+        except subprocess.CalledProcessError:
+            pass
+
+    thread = threading.Thread(target=run_cmd)
+    thread.start()
+    thread.join(timeout=COMPLETION_TIMEOUT)
+
+    if thread.is_alive():
+        return iter([])
+
+    services_dict = {name: "service" for name in services}
+    return services_dict
+
+
 def complete_secrets(
     prefix: str, parsed_args: argparse.Namespace, **kwargs: Any
 ) -> Iterable[str]: