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.common.utils;
  
  import java.util.Iterator;
  import java.util.function.Function;
  
  /**
   * Provides a flattened iterator over the inner elements of an outer iterator.
   */
  public final class FlattenedIterator<O, I> extends AbstractIterator<I> {
      private final Iterator<O> outerIterator;
      private final Function<O, Iterator<I>> innerIteratorFunction;
      private Iterator<I> innerIterator;
  
      public FlattenedIterator(Iterator<O> outerIterator, Function<O, Iterator<I>> innerIteratorFunction) {
          this.outerIterator = outerIterator;
          this.innerIteratorFunction = innerIteratorFunction;
      }
  
      @Override
      protected I makeNext() {
          while (innerIterator == null || !innerIterator.hasNext()) {
              if (outerIterator.hasNext())
                  innerIterator = innerIteratorFunction.apply(outerIterator.next());
              else
                  return allDone();
          }
          return innerIterator.next();
      }
  }
  