content: /*
   * Copyright 2014-2025 Real Logic Limited.
   *
   * Licensed 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
   *
   * https://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.agrona.collections;
  
  import java.util.AbstractCollection;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.function.Function;
  
  /**
   * An unmodifiable view of a collection that maps each element in an underlying collection into a view.
   *
   * @param <V> The type of the view.
   * @param <E> The type of the underlying element.
   */
  public class UnmodifiableCollectionView<V, E> extends AbstractCollection<V>
  {
      private final ReusableIterator iterator = new ReusableIterator();
      private final Function<E, V> viewer;
      private final Collection<E> elements;
  
      /**
       * Constructs an unmodifiable view over collection.
       *
       * @param viewer   function.
       * @param elements collection to create a view for.
       */
      public UnmodifiableCollectionView(final Function<E, V> viewer, final Collection<E> elements)
      {
          this.viewer = viewer;
          this.elements = elements;
      }
  
      /**
       * {@inheritDoc}
       */
      public int size()
      {
          return elements.size();
      }
  
      /**
       * {@inheritDoc}
       */
      public ReusableIterator iterator()
      {
          return iterator.reset();
      }
  
      /**
       * A stateful reusable iterator.
       */
      public final class ReusableIterator implements Iterator<V>
      {
          private Iterator<E> delegate;
  
          /**
           * Create a new instance.
           */
          public ReusableIterator()
          {
          }
  
          /**
           * {@inheritDoc}
           */
          public boolean hasNext()
          {
              return delegate.hasNext();
          }
  
          /**
           * {@inheritDoc}
           */
          public V next()
          {
              return viewer.apply(delegate.next());
          }
  
          private ReusableIterator reset()
          {
              delegate = elements.iterator();
  
              return this;
          }
      }
  }
  