Reuse _detect_user() and _expand_home() in simple_backup()

The entry point repeated both, and its copy of the '~' expansion missed a bare '~'.

simple_backup/simple_backup.py

@@ -1081,26 +1081,14 @@ def simple_backup() -> int:
 
     args = _parse_arguments()
 
-    if args.user:
-        user = args.user
-        homedir = os.path.expanduser(f'~{user}')
-    else:
-        euid = os.geteuid()
+    user: str | None = args.user or _detect_user()
 
-        if euid == 0:
-            user = _detect_user()
-
-            if user is not None:
-                homedir = os.path.expanduser(f'~{user}')
+    if not args.user and os.geteuid() != 0:
+        homedir = os.getenv('HOME', '')
+    elif user is not None:
+        homedir = _expand_home('~', user)
     else:
-                logger.warning(
-                    'Failed to detect user. You can use -u/--user parameter to manually specify it')
-                homedir = None
-        else:
-            user = os.getenv('USER')
-            homedir = os.getenv('HOME')
-
-    if homedir is None:
+        logger.warning('Failed to detect user. You can use -u/--user parameter to manually specify it')
         homedir = ''
 
     if args.no_syslog:
@@ -1109,13 +1097,8 @@ def simple_backup() -> int:
         except NameError:
             pass
 
-    config_file = args.config
-
     # Expand '~' to the home of the user running the backup, not root's
-    if config_file.startswith('~/') and user is not None:
-        config_file = f'~{user}{config_file[1:]}'
-
-    config_file = os.path.expanduser(config_file)
+    config_file = _expand_home(args.config, user) if user is not None else os.path.expanduser(args.config)
 
     try:
         config_args = _read_config(config_file, user)