content: /*
   * 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.List;
  import java.util.Objects;
  import java.util.stream.Collectors;
  import java.util.stream.Stream;
  import java.util.stream.StreamSupport;
  import org.apache.flink.api.common.state.ListState;
  import org.apache.flink.api.common.state.ListStateDescriptor;
  import org.apache.flink.api.java.functions.KeySelector;
  import org.apache.flink.runtime.state.KeyedStateBackend;
  import org.apache.flink.runtime.state.VoidNamespace;
  import org.apache.flink.runtime.state.VoidNamespaceSerializer;
  
  /**
   * {@link PushedBackElementsHandler} that stores elements in Flink keyed state, for use when an
   * operation is keyed and pushed-back data needs to stay in the correct partition when they get
   * moved.
   */
  class KeyedPushedBackElementsHandler<K, T> implements PushedBackElementsHandler<T> {
  
    static <K, T> KeyedPushedBackElementsHandler<K, T> create(
        KeySelector<T, K> keySelector,
        KeyedStateBackend<K> backend,
        ListStateDescriptor<T> stateDescriptor)
        throws Exception {
      return new KeyedPushedBackElementsHandler<>(keySelector, backend, stateDescriptor);
    }
  
    private final KeySelector<T, K> keySelector;
    private final KeyedStateBackend<K> backend;
    private final String stateName;
    private final ListState<T> state;
  
    private KeyedPushedBackElementsHandler(
        KeySelector<T, K> keySelector,
        KeyedStateBackend<K> backend,
        ListStateDescriptor<T> stateDescriptor)
        throws Exception {
      this.keySelector = Objects.requireNonNull(keySelector);
      this.backend = Objects.requireNonNull(backend);
      this.stateName = stateDescriptor.getName();
      // Eagerly retrieve the state to work around https://jira.apache.org/jira/browse/FLINK-12653
      this.state =
          backend.getPartitionedState(
              VoidNamespace.INSTANCE, VoidNamespaceSerializer.INSTANCE, stateDescriptor);
    }
  
    @Override
    public Stream<T> getElements() {
      return backend
          .getKeys(stateName, VoidNamespace.INSTANCE)
          .flatMap(
              key -> {
                try {
                  backend.setCurrentKey(key);
                  return StreamSupport.stream(state.get().spliterator(), false);
                } catch (Exception e) {
                  throw new RuntimeException("Error reading keyed state.", e);
                }
              });
    }
  
    @Override
    public void clear() throws Exception {
      // TODO we have to collect all keys because otherwise we get ConcurrentModificationExceptions
      // from flink. We can change this once it's fixed in Flink
      List<K> keys = backend.getKeys(stateName, VoidNamespace.INSTANCE).collect(Collectors.toList());
  
      for (K key : keys) {
        backend.setCurrentKey(key);
        state.clear();
      }
    }
  
    @Override
    public void pushBack(T element) throws Exception {
      backend.setCurrentKey(keySelector.getKey(element));
      state.add(element);
    }
  
    @Override
    public void pushBackAll(Iterable<T> elements) throws Exception {
      for (T e : elements) {
        pushBack(e);
      }
    }
  }
  