"""Object Utilities."""


class cached_property:
    """Cached property descriptor.

    Caches the return value of the get method on first call.

    Examples:
        .. code-block:: python

            @cached_property
            def connection(self):
                return Connection()

            @connection.setter  # Prepares stored value
            def connection(self, value):
                if value is None:
                    raise TypeError('Connection must be a connection')
                return value

            @connection.deleter
            def connection(self, value):
                # Additional action to do at del(self.attr)
                if value is not None:
                    print('Connection {0!r} deleted'.format(value)
    """

    def __init__(self, fget=None, fset=None, fdel=None, doc=None):
        self.__get = fget
        self.__set = fset
        self.__del = fdel
        self.__doc__ = doc or fget.__doc__
        self.__name__ = fget.__name__
        self.__module__ = fget.__module__

    def __get__(self, obj, type=None):
        if obj is None:
            return self
        try:
            return obj.__dict__[self.__name__]
        except KeyError:
            value = obj.__dict__[self.__name__] = self.__get(obj)
            return value

    def __set__(self, obj, value):
        if obj is None:
            return self
        if self.__set is not None:
            value = self.__set(obj, value)
        obj.__dict__[self.__name__] = value

    def __delete__(self, obj, _sentinel=object()):
        if obj is None:
            return self
        value = obj.__dict__.pop(self.__name__, _sentinel)
        if self.__del is not None and value is not _sentinel:
            self.__del(obj, value)

    def setter(self, fset):
        return self.__class__(self.__get, fset, self.__del)

    def deleter(self, fdel):
        return self.__class__(self.__get, self.__set, fdel)
