Updated parser.py

- Changed class@SoypakParser => class@_SoypackParser
- class@SoypakParser is now a singleton pattern which handles
  class@_SoypakParser.
- SoypakParser@add_action_command (static method): add a command to the
  action group (argparser).

soypak/cli/parser.py

@@ -16,13 +16,15 @@ class OverrideHelpFormatter(argparse.RawDescriptionHelpFormatter, argparse.HelpF
         return super().add_usage(usage, actions, groups, 'Usage: ')
 
 
-class SoypakParser(argparse.ArgumentParser):
+class _SoypakParser(argparse.ArgumentParser):
     """soypak parsing and translating program arguments given by `sys.argv`.
 
-    Class constructs a custom help message display which is shown with arguments `-h|--help` or when an invalid argument
-    is passed. There is mangling of attributes in in the parent class to provide a modern, simplistic, and coherent help
-    message display found with other package managers.
+    Class is to not be directly constructed and initialised. Use `SoypakParser` which implements a singleton pattern and
+    controls this class.
     """
+
+    _action_groups__ = []
+
     def __init__(self) -> None:
         self.NAME = module_info.__title__
         USAGE = "%(prog)s [options] <command> [arguments]"
@@ -56,13 +58,10 @@ class SoypakParser(argparse.ArgumentParser):
         self.add_argument("command", nargs='?')
 
         # overwrite the action group. @Note: this is to give custom positional arguments in the help message but aren't
-        # actual arguments. They are stored in the "command" attribute (defined above).
-        # :@TODO: When commands are registered, allow the register to submit info for the action group. This overwrite
-        # will then be configured using all the register commands.
-        self._positionals._group_actions = []
-        ### argparse._StoreAction(option_strings=[], dest=cmd, help=desc)
+        # actual arguments. They are stored in the "command" action (defined above).
+        self._positionals._group_actions = _SoypakParser._action_groups__
 
-        # optional arguments
+        # optional arguments - stored in the Namespace
         self.add_argument("--version", action="store_true",
                           help="show the program's version number and exit")
 
@@ -71,4 +70,28 @@ class SoypakParser(argparse.ArgumentParser):
         # we use `parse_known_args` to allow for splitting of largs/rargs
         self.namespace, self.rargs = self.parse_known_args()
 
+        # return just the command collected and the rargs
         return (self.namespace.command, self.rargs)
+
+
+class SoypakParser:
+    """soypak parsing and translating program arguments given by `sys.argv`.
+
+    Class constructs a custom help message display which is shown with arguments `-h|--help` or when an invalid argument
+    is passed. There is mangling of attributes in in the parent class to provide a modern, simplistic, and coherent help
+    message display found with other package managers.
+    """
+    # Singleton pattern
+    __instance__ = None
+    def __new__(cls) -> _SoypakParser:
+        if not SoypakParser.__instance__:
+            SoypakParser.__instance__ = _SoypakParser()
+
+        return SoypakParser.__instance__
+
+
+    @staticmethod
+    def add_action_command(*, cmd, help):
+        _SoypakParser._action_groups__.append(
+            argparse._StoreAction(option_strings=[], dest=cmd, help=help)
+        )