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.kafka.streams.state.internals;
  
  import org.apache.kafka.streams.KeyValue;
  import org.apache.kafka.streams.state.KeyValueIterator;
  
  import java.util.NoSuchElementException;
  
  /**
   * Optimized {@link KeyValueIterator} used when the same element could be peeked multiple times.
   */
  public class DelegatingPeekingKeyValueIterator<K, V> implements KeyValueIterator<K, V>, PeekingKeyValueIterator<K, V> {
      private final KeyValueIterator<K, V> underlying;
      private final String storeName;
      private KeyValue<K, V> next;
  
      private volatile boolean open = true;
  
      public DelegatingPeekingKeyValueIterator(final String storeName, final KeyValueIterator<K, V> underlying) {
          this.storeName = storeName;
          this.underlying = underlying;
      }
  
      @Override
      public synchronized K peekNextKey() {
          if (!hasNext()) {
              throw new NoSuchElementException();
          }
          return next.key;
      }
  
      @Override
      public synchronized void close() {
          underlying.close();
          open = false;
      }
  
      @Override
      public synchronized boolean hasNext() {
          if (!open) {
              throw new IllegalStateException(String.format("Iterator for store %s has already been closed.", storeName));
          }
          if (next != null) {
              return true;
          }
  
          if (!underlying.hasNext()) {
              return false;
          }
  
          next = underlying.next();
          return true;
      }
  
      @Override
      public synchronized KeyValue<K, V> next() {
          if (!hasNext()) {
              throw new NoSuchElementException();
          }
          final KeyValue<K, V> result = next;
          next = null;
          return result;
      }
  
      @Override
      public KeyValue<K, V> peekNext() {
          if (!hasNext()) {
              throw new NoSuchElementException();
          }
          return next;
      }
  }
  