# -*- coding: utf-8 -*-
#
#  Copyright (c) 2010—2013 Andrey Mikhaylenko and contributors
#
#  This file is part of Argh.
#
#  Argh is free software under terms of the GNU Lesser
#  General Public License version 3 (LGPLv3) as published by the Free
#  Software Foundation. See the file README for copying conditions.
#
"""
Utilities
~~~~~~~~~
"""
import argparse
import inspect

from argh import compat


def get_subparsers(parser, create=False):
    """Returns the :class:`argparse._SubParsersAction` instance for given
    :class:`ArgumentParser` instance as would have been returned by
    :meth:`ArgumentParser.add_subparsers`. The problem with the latter is that
    it only works once and raises an exception on the second attempt, and the
    public API seems to lack a method to get *existing* subparsers.

    :param create:
        If `True`, creates the subparser if it does not exist. Default if
        `False`.

    """
    # note that ArgumentParser._subparsers is *not* what is returned by
    # ArgumentParser.add_subparsers().
    if parser._subparsers:
        actions = [a for a in parser._actions
                   if isinstance(a, argparse._SubParsersAction)]
        assert len(actions) == 1
        return actions[0]
    else:
        if create:
            return parser.add_subparsers()


def get_arg_names(function):
    """Returns argument names for given function.  Omits special arguments
    of instance methods (`self`) and static methods (usually `cls` or something
    like this).
    """
    spec = compat.getargspec(function)
    names = spec.args

    if not names:
        return []

    if inspect.ismethod(function):
        return names[1:]
    else:
        return names