import collections
import inspect


FullArgSpec = collections.namedtuple(
    "FullArgSpec",
    [
        "args",
        "varargs",
        "varkw",
        "defaults",
        "kwonlyargs",
        "kwonlydefaults",
        "annotations",
    ],
)

ArgSpec = collections.namedtuple(
    "ArgSpec", ["args", "varargs", "keywords", "defaults"]
)


def inspect_getfullargspec(func):
    """Fully vendored version of getfullargspec from Python 3.3.

    This version is more performant than the one which appeared in
    later Python 3 versions.

    """

    # if a Signature is already present, as is the case with newer
    # "decorator" package, defer back to built in
    if hasattr(func, "__signature__"):
        return inspect.getfullargspec(func)

    if inspect.ismethod(func):
        func = func.__func__
    if not inspect.isfunction(func):
        raise TypeError("{!r} is not a Python function".format(func))

    co = func.__code__
    if not inspect.iscode(co):
        raise TypeError("{!r} is not a code object".format(co))

    nargs = co.co_argcount
    names = co.co_varnames
    nkwargs = co.co_kwonlyargcount
    args = list(names[:nargs])
    kwonlyargs = list(names[nargs : nargs + nkwargs])

    nargs += nkwargs
    varargs = None
    if co.co_flags & inspect.CO_VARARGS:
        varargs = co.co_varnames[nargs]
        nargs = nargs + 1
    varkw = None
    if co.co_flags & inspect.CO_VARKEYWORDS:
        varkw = co.co_varnames[nargs]

    return FullArgSpec(
        args,
        varargs,
        varkw,
        func.__defaults__,
        kwonlyargs,
        func.__kwdefaults__,
        func.__annotations__,
    )


def inspect_getargspec(func):
    return ArgSpec(*inspect_getfullargspec(func)[0:4])