import functools
import pymongo
import logging
import time

MAX_AUTO_RECONNECT_ATTEMPTS = 5

def graceful_auto_reconnect(mongo_op_func):
  """Gracefully handle a reconnection event."""
  @functools.wraps(mongo_op_func)
  def wrapper(*args, **kwargs):
    for attempt in xrange(MAX_AUTO_RECONNECT_ATTEMPTS):
      try:
        return mongo_op_func(*args, **kwargs)
      except pymongo.errors.AutoReconnect as e:
        wait_t = 0.5 * pow(2, attempt) # exponential back off
        logging.warning("PyMongo auto-reconnecting... %s. Waiting %.1f seconds.", str(e), wait_t)
        time.sleep(wait_t)

  return wrapper