import datetime
import os.path as op

VERSION = datetime.datetime.now()
VERSION_TIME = str(VERSION).split('.')[0]
for c in [' ', ':', '-']:
    VERSION_TIME = VERSION_TIME.replace(c, '_')

def get_root_path() -> str:
    return op.dirname(op.abspath(__file__))


def get_full_path(relative_path: str) -> str:
    return op.join(get_root_path(), relative_path)


def get_display_name_from_object_type(object_type):
    # assert isinstance(object_type, type), object_type
    return str(object_type).split('.')[-1].split("'")[0].split(' ')[0]


def first(s):
    """Return the first element from an ordered collection
       or an arbitrary element from an unordered collection.
       Raise StopIteration if the collection is empty.
    """
    return next(iter(s))


# todo: these cached property have a weird behavior with inheritence,
#  when we call the super cached_property in the child method
class cached_property(object):
    """
    Descriptor (non-data) for building an attribute on-demand on first use.
    From: https://stackoverflow.com/questions/4037481/caching-attributes-of-classes-in-python
    """

    def __init__(self, factory):
        """
        <factory> is called such: factory(instance) to build the attribute.
        """
        self._attr_name = factory.__name__
        self._factory = factory

    def __get__(self, instance, owner):
        # Build the attribute.
        attr = self._factory(instance)

        # Cache the value; hide ourselves.
        setattr(instance, self._attr_name, attr)

        return attr


class Example(object):

    @cached_property
    def big_attribute(self):
        print('Long loading only once...')
        return 2


if __name__ == '__main__':
    e = Example()
    print(e.big_attribute)
    print(e.big_attribute)
    print(VERSION_TIME)