#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""http://code.activestate.com/recipes/413838-memento-closure/"""

from copy import copy, deepcopy


def memento(obj, deep=False):
    state = copy(obj.__dict__) if deep else deepcopy(obj.__dict__)

    def restore():
        obj.__dict__.clear()
        obj.__dict__.update(state)

    return restore


class Transaction:
    """A transaction guard.
    This is, in fact, just syntactic sugar around a memento closure.
    """
    deep = False
    states = []

    def __init__(self, *targets):
        self.targets = targets
        self.commit()

    def commit(self):
        self.states = [memento(target, self.deep) for target in self.targets]

    def rollback(self):
        for a_state in self.states:
            a_state()


class Transactional(object):
    """Adds transactional semantics to methods. Methods decorated  with
    @Transactional will rollback to entry-state upon exceptions.
    """

    def __init__(self, method):
        self.method = method

    def __get__(self, obj, T):
        def transaction(*args, **kwargs):
            state = memento(obj)
            try:
                return self.method(obj, *args, **kwargs)
            except Exception as e:
                state()
                raise e

        return transaction


class NumObj(object):
    def __init__(self, value):
        self.value = value

    def __repr__(self):
        return '' % (self.__class__.__name__, self.value)

    def increment(self):
        self.value += 1

    @Transactional
    def do_stuff(self):
        self.value = '1111'  #  doing stuff failed!
# Traceback (most recent call last):
# File "memento.py", line 97, in 
#     num_obj.do_stuff()
#   File "memento.py", line 52, in transaction
#     raise e
#   File "memento.py", line 49, in transaction
#     return self.method(obj, *args, **kwargs)
#   File "memento.py", line 70, in do_stuff
#     self.increment()     #