from django.db.models.signals import post_save

from .models import UserStorage
from .multi import MultiStorage

class BYOStorage(MultiStorage):
    ''' Database driven Bring-Your-Own-Storage

    '''

    def __init__(self, config=None):
        super(BYOStorage, self).__init__(config)

        post_save.connect(self.handle_change, sender=UserStorage)


    def handle_change(self, instance, **kwargs):
        try:
            del(self._cache[instance.name])
        except KeyError:
            pass

    def get_storage(self, name):
        if name not in self._cache:

            # use storage from config by default
            if name in self.config:
                return super(BYOStorage, self).get_storage(name)

            obj = UserStorage.objects.get(name=name)
            self._cache[name] = obj.instance()
        return self._cache[name]