/*
    * 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.eclipse.aether.util.listener;
  
  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 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);
         }
     }
 
     /**
      * Invoked when any listener throws, by default is no op, extend if required.
      */
     @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);
             }
         }
     }
 }