from google.appengine.ext import db

def iterative_task(logic, **task_default):

  Args:

    logic: the Logic instance to get entities for

    task_default: keyword arguments which can contain the following options:

      fields: dictionary to filter the entities on

      start_key: the default key where to start this iterative task

  def wrapper(func):

    def iterative_wrapped(request, *args, **kwargs):

      """Decorator wrapper method

      Args:

        request: Django HTTP Request object

      request.POST usage:

        fields: a JSON dict for the properties that the entities should have.

          This updates values from the task_default entry.

        start_key: the key of the next entity to fetch

      Returns:

        Standard HTTP Django response

      """

      post_dict = request.POST

      fields = task_default.get('fields', {})

      if 'fields' in post_dict:

        fields.update(simplejson.loads(post_dict['fields']))

      start_key = task_default.get('start_key', None)

      if 'start_key' in post_dict:

        # get the key where to start this iteration

        start_key = post_dict['start_key']

      if start_key:

        start_key = db.Key(start_key)

      # get the entities for this iteration

      entities, next_start_key = logic.getBatchOfData(filter=fields,

                                                      start_key=start_key)

      # copy the post_dict so that the wrapped function can edit what it needs

      try:

        func(request, entities=entities, context=context, *args, **kwargs)

      except task_responses.FatalTaskError, error:

        logging.error(error)

        return task_responses.terminateTask()

      except Exception, exception:

        logging.error(exception)

        return task_responses.repeatTask()

      if next_start_key:

        # set the key to use for the next iteration

        context.update({'start_key': next_start_key})

        task_responses.startTask(url=request.path, context=context)

      return task_responses.terminateTask()

    return iterative_wrapped

  return wrapper