from django.conf import settings
from django.core.cache import cache
from django.contrib.auth.models import User
from django.utils.deprecation import MiddlewareMixin
from django.contrib.auth import user_logged_out
from django.dispatch import receiver

ONLINE_THRESHOLD = getattr(settings, 'ONLINE_THRESHOLD', 60 * 15)
ONLINE_MAX = getattr(settings, 'ONLINE_MAX', 50)


def get_online_now(self):
    return User.objects.filter(id__in=self.online_now_ids or [])


@receiver(user_logged_out)
def logout(sender, **kwargs):
    try:
        cache.delete('online-%s' % kwargs['user'].id)
    except AttributeError:
        pass


class OnlineNowMiddleware(MiddlewareMixin):
    """Maintains a list of users who have interacted with the website recently.

    Their user IDs are available as ``online_now_ids`` on the request
    object, and their corresponding users are available (lazily) as the
    ``online_now`` property on the request object.

    """

    def process_request(self, request):
        # First get the index
        uids = cache.get('online-now', [])

        # Perform the multiget on the individual online uid keys
        online_keys = ['online-%s' % (u,) for u in uids]
        fresh = cache.get_many(online_keys).keys()
        online_now_ids = [int(k.replace('online-', '')) for k in fresh]

        # If the user is authenticated, add their id to the list
        if request.user.is_authenticated:
            uid = request.user.id
            # If their uid is already in the list, we want to bump it
            # to the top, so we remove the earlier entry.
            if uid in online_now_ids:
                online_now_ids.remove(uid)
            online_now_ids.append(uid)
            if len(online_now_ids) > ONLINE_MAX:
                del online_now_ids[0]

        # Attach our modifications to the request object
        request.__class__.online_now_ids = online_now_ids
        request.__class__.online_now = property(get_online_now)

        # Set the new cache
        cache.set('online-%s' % (request.user.pk,), True, ONLINE_THRESHOLD)
        cache.set('online-now', online_now_ids, ONLINE_THRESHOLD)