#!/usr/bin/env python
# -*- encoding: utf-8 -*-

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'''custom_grouping.py: interface module for custom grouping'''
from abc import abstractmethod

class ICustomGrouping(object):
  '''Interface for custom grouping class'''

  @abstractmethod
  def prepare(self, context, component, stream, target_tasks):
    """Tells the stream grouping at runtime the tasks in the target bolt

    This information should be used in ``choose_tasks()`` to determine the target tasks.

    :param context: topology-worker context
    :param component: source component name
    :param stream: stream id used for this grouping
    :type target_tasks: list of int
    :param target_tasks: list of target task ids
    """
    pass

  @abstractmethod
  def choose_tasks(self, values):
    """Implements a custom stream grouping

    :param values: the values to group on
    :rtype: list of int
    :return: list of task ids to which these values are emitted
    """
    pass