package org.eclipse.aether.util.listener;
   
   /*
    * 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.
   */
  
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.List;
  import java.util.concurrent.CopyOnWriteArrayList;
  
  import org.eclipse.aether.transfer.AbstractTransferListener;
  import org.eclipse.aether.transfer.TransferCancelledException;
  import org.eclipse.aether.transfer.TransferEvent;
  import org.eclipse.aether.transfer.TransferListener;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * A transfer listener that delegates to zero or more other listeners (multicast). The list of target listeners is
   * thread-safe, i.e. target listeners can be added or removed by any thread at any time.
   */
  public final class ChainedTransferListener
      extends AbstractTransferListener
  {
  
      private final List<TransferListener> listeners = new CopyOnWriteArrayList<>();
  
      /**
       * Creates a new multicast listener that delegates to the specified listeners. In contrast to the constructor, this
       * factory method will avoid creating an actual chained listener if one of the specified readers is actually
       * {@code null}.
       * 
       * @param listener1 The first listener, may be {@code null}.
       * @param listener2 The second listener, may be {@code null}.
       * @return The chained listener or {@code null} if no listener was supplied.
       */
      public static TransferListener newInstance( TransferListener listener1, TransferListener listener2 )
      {
          if ( listener1 == null )
          {
              return listener2;
          }
          else if ( listener2 == null )
          {
              return listener1;
          }
          return new ChainedTransferListener( listener1, listener2 );
      }
  
      /**
       * Creates a new multicast listener that delegates to the specified listeners.
       * 
       * @param listeners The listeners to delegate to, may be {@code null} or empty.
       */
      public ChainedTransferListener( TransferListener... listeners )
      {
          if ( listeners != null )
          {
              add( Arrays.asList( listeners ) );
          }
      }
  
      /**
       * Creates a new multicast listener that delegates to the specified listeners.
       * 
       * @param listeners The listeners to delegate to, may be {@code null} or empty.
       */
      public ChainedTransferListener( Collection<? extends TransferListener> listeners )
      {
          add( listeners );
      }
  
      /**
       * Adds the specified listeners to the end of the multicast chain.
       * 
       * @param listeners The listeners to add, may be {@code null} or empty.
       */
      public void add( Collection<? extends TransferListener> listeners )
      {
          if ( listeners != null )
          {
              for ( TransferListener listener : listeners )
              {
                 add( listener );
             }
         }
     }
 
     /**
      * Adds the specified listener to the end of the multicast chain.
      * 
      * @param listener The listener to add, may be {@code null}.
      */
     public void add( TransferListener listener )
     {
         if ( listener != null )
         {
             listeners.add( listener );
         }
     }
 
     /**
      * Removes the specified listener from the multicast chain. Trying to remove a non-existing listener has no effect.
      * 
      * @param listener The listener to remove, may be {@code null}.
      */
     public void remove( TransferListener listener )
     {
         if ( listener != null )
         {
             listeners.remove( listener );
         }
     }
 
     @SuppressWarnings( "EmptyMethod" )
     protected void handleError( TransferEvent event, TransferListener listener, RuntimeException error )
     {
         // default just swallows errors
     }
 
     @Override
     public void transferInitiated( TransferEvent event )
         throws TransferCancelledException
     {
         requireNonNull( event, "event cannot be null" );
         for ( TransferListener listener : listeners )
         {
             try
             {
                 listener.transferInitiated( event );
             }
             catch ( RuntimeException e )
             {
                 handleError( event, listener, e );
             }
         }
     }
 
     @Override
     public void transferStarted( TransferEvent event )
         throws TransferCancelledException
     {
         requireNonNull( event, "event cannot be null" );
         for ( TransferListener listener : listeners )
         {
             try
             {
                 listener.transferStarted( event );
             }
             catch ( RuntimeException e )
             {
                 handleError( event, listener, e );
             }
         }
     }
 
     @Override
     public void transferProgressed( TransferEvent event )
         throws TransferCancelledException
     {
         requireNonNull( event, "event cannot be null" );
         for ( TransferListener listener : listeners )
         {
             try
             {
                 listener.transferProgressed( event );
             }
             catch ( RuntimeException e )
             {
                 handleError( event, listener, e );
             }
         }
     }
 
     @Override
     public void transferCorrupted( TransferEvent event )
         throws TransferCancelledException
     {
         requireNonNull( event, "event cannot be null" );
         for ( TransferListener listener : listeners )
         {
             try
             {
                 listener.transferCorrupted( event );
             }
             catch ( RuntimeException e )
             {
                 handleError( event, listener, e );
             }
         }
     }
 
     @Override
     public void transferSucceeded( TransferEvent event )
     {
         requireNonNull( event, "event cannot be null" );
         for ( TransferListener listener : listeners )
         {
             try
             {
                 listener.transferSucceeded( event );
             }
             catch ( RuntimeException e )
             {
                 handleError( event, listener, e );
             }
         }
     }
 
     @Override
     public void transferFailed( TransferEvent event )
     {
         requireNonNull( event, "event cannot be null" );
         for ( TransferListener listener : listeners )
         {
             try
             {
                 listener.transferFailed( event );
             }
             catch ( RuntimeException e )
             {
                 handleError( event, listener, e );
             }
         }
     }
 
 }