mooraker: refactor main entry point

Move the version check to the top of the module.   An older version
of python is unlikely to make it beyond the initial import statements,
so print a message to stdout and stderr.

Move argument parsing out of the main method.  This makes it possible
to invoke main without parsing command line arguments, which is useful
for tests.

Signed-off-by: Eric Callahan <arksine.code@gmail.com>

moonraker/moonraker.py

@@ -6,8 +6,16 @@
 # This file may be distributed under the terms of the GNU GPLv3 license
 
 from __future__ import annotations
-import argparse
 import sys
+if sys.version_info < (3, 7):
+    msg = (
+        "Moonraker requires Python 3.7 or above.  "
+        "Detected Version: %s\n"
+    )
+    sys.stdout.write(msg % (sys.version,))
+    sys.stderr.write(msg % (sys.version,))
+    exit(1)
+import argparse
 import importlib
 import os
 import io
@@ -858,21 +866,7 @@ class BaseRequest:
         return {'id': self.id, 'method': self.rpc_method,
                 'params': self.params}
 
-def main() -> None:
-    # Parse start arguments
-    parser = argparse.ArgumentParser(
-        description="Moonraker - Klipper API Server")
-    parser.add_argument(
-        "-c", "--configfile", default="~/moonraker.conf",
-        metavar='<configfile>',
-        help="Location of moonraker configuration file")
-    parser.add_argument(
-        "-l", "--logfile", default="/tmp/moonraker.log", metavar='<logfile>',
-        help="log file name and location")
-    parser.add_argument(
-        "-n", "--nologfile", action='store_true',
-        help="disable logging to a file")
-    cmd_line_args = parser.parse_args()
+def main(cmd_line_args: argparse.Namespace) -> None:
     cfg_file = cmd_line_args.configfile
     app_args = {'config_file': cfg_file}
 
@@ -888,14 +882,6 @@ def main() -> None:
     if warning is not None:
         app_args['log_warning'] = warning
 
-    if sys.version_info < (3, 7):
-        msg = f"Moonraker requires Python 3.7 or above.  " \
-            f"Detected Version: {sys.version}"
-        logging.info(msg)
-        print(msg)
-        ql.stop()
-        exit(1)
-
     # Start asyncio event loop and server
     event_loop = EventLoop()
     alt_config_loaded = False
@@ -964,4 +950,17 @@ def main() -> None:
 
 
 if __name__ == '__main__':
-    main()
+    # Parse start arguments
+    parser = argparse.ArgumentParser(
+        description="Moonraker - Klipper API Server")
+    parser.add_argument(
+        "-c", "--configfile", default="~/moonraker.conf",
+        metavar='<configfile>',
+        help="Location of moonraker configuration file")
+    parser.add_argument(
+        "-l", "--logfile", default="/tmp/moonraker.log", metavar='<logfile>',
+        help="log file name and location")
+    parser.add_argument(
+        "-n", "--nologfile", action='store_true',
+        help="disable logging to a file")
+    main(parser.parse_args())