class Snapshot(models.Model):
    tournament = models.ForeignKey('Tournament')
    name = models.CharField(null=True)
    created_at = models.DateTimeField()
    data = JSONField()



class Memento:
    def __init__(self, snapshot_id, state):
        self.snapshot_id = snapshot_id  # saved snapshot corresponding to this memento
        self.state = state  # serialized schedule data dictionary


class Originator:
    def __init__(self, tournament):
        self.tournament = tournament

    def set(self, snapshot_name=None):
        self.state = serialize_schedule(self.tournament)
        self.name = snapshot_name

    def create_memento(self):
        snapshot = Snapshot.objects.create(tournament=self.tournament, name=self.name,
                                           created_at=datetime.datetime.now(), data=self.state)
        return Memento(snapshot.id, self.state)

    def restore(self, memento):
        data = deserialize_schedule(self.tournament, memento.state)
        with transaction.atomic():
            delete_schedule()  # delete current schedule
            create_schedule(data)  # create schedule with the memento state data


class Caretaker:
    def __init__(self, tournament):
        self.tournament = tournament
        self.originator = Originator(tournament)
        self.saved_states = list(Snapshot.objects.filter(tournament=tournament).values_list('id', flat=True))

    def create_snapshot(self, *args):
        self.originator.set(*args)
        memento = self.originator.create_memento()
        self.saved_states.append(memento.snapshot_id)

    def restore(self, snapshot_id):
        snapshot = self.tournament.snapshot_set.get(id=snapshot_id)
        memento = Memento(snapshot_id, snapshot.data)
        self.originator.restore(memento)