/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.beam.runners.flink.translation.wrappers.streaming;

import java.util.stream.Stream;

/**
 * Helper that keeps pushed-back data, most likely due to side inputs that are not available.
 *
 * <p>Implementations of this must use Flink state to make sure pushed-back data is fault tolerant.
 *
 * @param <T> The type of pushed back elements.
 */
interface PushedBackElementsHandler<T> {

  /** Returns all pushed back elements. */
  Stream<T> getElements() throws Exception;

  /** Clears the pushed back elements. */
  void clear() throws Exception;

  /** Adds the given element to the pushed back elements. */
  void pushBack(T element) throws Exception;

  /** Adds all the given element to the pushed back elements. */
  void pushBackAll(Iterable<T> elements) throws Exception;
}
