# -*- coding=utf-8 -*-
from __future__ import absolute_import, unicode_literals

from functools import partial


__all__ = ["partialmethod",]


class partialmethod(object):
    """Method descriptor with partial application of the given arguments
    and keywords.
    Supports wrapping existing descriptors and handles non-descriptor
    callables as instance methods.
    """

    def __init__(self, func, *args, **keywords):
        if not callable(func) and not hasattr(func, "__get__"):
            raise TypeError("{!r} is not callable or a descriptor"
                                .format(func))

        # func could be a descriptor like classmethod which isn't callable,
        # so we can't inherit from partial (it verifies func is callable)
        if isinstance(func, partialmethod):
            # flattening is mandatory in order to place cls/self before all
            # other arguments
            # it's also more efficient since only one function will be called
            self.func = func.func
            self.args = func.args + args
            self.keywords = func.keywords.copy()
            self.keywords.update(keywords)
        else:
            self.func = func
            self.args = args
            self.keywords = keywords

    def __repr__(self):
        args = ", ".join(map(repr, self.args))
        keywords = ", ".join("{}={!r}".format(k, v)
                                for k, v in self.keywords.items())
        format_string = "{module}.{cls}({func}, {args}, {keywords})"
        return format_string.format(module=self.__class__.__module__,
                                    cls=self.__class__.__qualname__,
                                    func=self.func,
                                    args=args,
                                    keywords=keywords)

    def _make_unbound_method(self):
        def _method(*args, **keywords):
            call_keywords = self.keywords.copy()
            call_keywords.update(keywords)
            if len(args) > 1:
                cls_or_self, rest = args[0], tuple(args[1:],)
            else:
                cls_or_self = args[0]
                rest = tuple()
            call_args = (cls_or_self,) + self.args + tuple(rest)
            return self.func(*call_args, **call_keywords)
        _method.__isabstractmethod__ = self.__isabstractmethod__
        _method._partialmethod = self
        return _method

    def __get__(self, obj, cls):
        get = getattr(self.func, "__get__", None)
        result = None
        if get is not None:
            new_func = get(obj, cls)
            if new_func is not self.func:
                # Assume __get__ returning something new indicates the
                # creation of an appropriate callable
                result = partial(new_func, *self.args, **self.keywords)
                try:
                    result.__self__ = new_func.__self__
                except AttributeError:
                    pass
        if result is None:
            # If the underlying descriptor didn't do anything, treat this
            # like an instance method
            result = self._make_unbound_method().__get__(obj, cls)
        return result

    @property
    def __isabstractmethod__(self):
        return getattr(self.func, "__isabstractmethod__", False)
