import inspect
import sys

from .dispatcher import Dispatcher, MethodDispatcher

global_namespace = dict()  # type: ignore[var-annotated]


def dispatch(*types, **kwargs):
    """ Dispatch function on the types of the inputs
    Supports dispatch on all non-keyword arguments.
    Collects implementations based on the function name.  Ignores namespaces.
    If ambiguous type signatures occur a warning is raised when the function is
    defined suggesting the additional method to break the ambiguity.
    Examples
    --------
    >>> @dispatch(int)
    ... def f(x):
    ...     return x + 1
    >>> @dispatch(float)
    ... def f(x):
    ...     return x - 1
    >>> f(3)
    4
    >>> f(3.0)
    2.0
    Specify an isolated namespace with the namespace keyword argument
    >>> my_namespace = dict()
    >>> @dispatch(int, namespace=my_namespace)
    ... def foo(x):
    ...     return x + 1
    Dispatch on instance methods within classes
    >>> class MyClass(object):
    ...     @dispatch(list)
    ...     def __init__(self, data):
    ...         self.data = data
    ...     @dispatch(int)
    ...     def __init__(self, datum):
    ...         self.data = [datum]
    """
    namespace = kwargs.get('namespace', global_namespace)

    types = tuple(types)

    def _df(func):
        name = func.__name__

        if ismethod(func):
            dispatcher = inspect.currentframe().f_back.f_locals.get(  # type: ignore[union-attr]
                name,  # type: ignore[union-attr]
                MethodDispatcher(name),
            )
        else:
            if name not in namespace:
                namespace[name] = Dispatcher(name)
            dispatcher = namespace[name]

        dispatcher.add(types, func)
        return dispatcher
    return _df


def ismethod(func):
    """ Is func a method?
    Note that this has to work as the method is defined but before the class is
    defined.  At this stage methods look like functions.
    """
    if hasattr(inspect, "signature"):
        signature = inspect.signature(func)
        return signature.parameters.get('self', None) is not None
    else:
        if sys.version_info.major < 3:
            spec = inspect.getargspec(func)
        else:
            spec = inspect.getfullargspec(func)  # type: ignore[union-attr, assignment]
        return spec and spec.args and spec.args[0] == 'self'
