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Java 1.6+ Library with tons of utility classes required in all projects
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/**
 * Copyright (C) 2014-2016 Philip Helger (www.helger.com)
 * philip[at]helger[dot]com
 *
 * 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
 *
 *         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 com.helger.commons.callback;

import java.util.function.Consumer;
import java.util.function.Function;

import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.GuardedBy;
import javax.annotation.concurrent.ThreadSafe;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.helger.commons.ValueEnforcer;
import com.helger.commons.annotation.ReturnsMutableCopy;
import com.helger.commons.collection.ext.CommonsLinkedHashSet;
import com.helger.commons.collection.ext.ICommonsList;
import com.helger.commons.collection.ext.ICommonsOrderedSet;
import com.helger.commons.concurrent.SimpleReadWriteLock;
import com.helger.commons.lang.ICloneable;
import com.helger.commons.state.EChange;
import com.helger.commons.state.EContinue;
import com.helger.commons.string.ToStringGenerator;

/**
 * This class manages a list of callbacks.
 *
 * @author Philip Helger
 * @param 
 *        The callback type.
 */
@ThreadSafe
public class CallbackList 
                          implements ICallbackList , ICloneable >
{
  private static final Logger s_aLogger = LoggerFactory.getLogger (CallbackList.class);

  private final SimpleReadWriteLock m_aRWLock = new SimpleReadWriteLock ();

  @GuardedBy ("m_aRWLock")
  private final ICommonsOrderedSet  m_aCallbacks = new CommonsLinkedHashSet<> ();

  public CallbackList ()
  {}

  public CallbackList (@Nonnull final CallbackList  aOther)
  {
    ValueEnforcer.notNull (aOther, "Other");
    m_aCallbacks.addAll (aOther.m_aCallbacks);
  }

  /**
   * Add a callback.
   *
   * @param aCallback
   *        May not be null.
   * @return this
   */
  @Nonnull
  public CallbackList  addCallback (@Nonnull final CALLBACKTYPE aCallback)
  {
    ValueEnforcer.notNull (aCallback, "Callback");

    m_aRWLock.writeLocked ( () -> m_aCallbacks.add (aCallback));
    return this;
  }

  /**
   * Remove the specified callback
   *
   * @param aCallback
   *        May be null.
   * @return {@link EChange}
   */
  @Nonnull
  public EChange removeCallback (@Nullable final CALLBACKTYPE aCallback)
  {
    if (aCallback == null)
      return EChange.UNCHANGED;

    return m_aRWLock.writeLocked ( () -> m_aCallbacks.removeObject (aCallback));
  }

  /**
   * Remove all callbacks
   *
   * @return {@link EChange}
   */
  @Nonnull
  public EChange removeAllCallbacks ()
  {
    return m_aRWLock.writeLocked ( () -> m_aCallbacks.removeAll ());
  }

  @Nonnull
  @ReturnsMutableCopy
  public ICommonsList  getAllCallbacks ()
  {
    return m_aRWLock.readLocked ( () -> m_aCallbacks.getCopyAsList ());
  }

  @Nullable
  public CALLBACKTYPE getCallbackAtIndex (@Nonnegative final int nIndex)
  {
    return m_aRWLock.readLocked ( () -> m_aCallbacks.getAtIndex (nIndex));
  }

  @Nonnegative
  public int getCallbackCount ()
  {
    return m_aRWLock.readLocked ( () -> m_aCallbacks.size ());
  }

  public boolean hasCallbacks ()
  {
    return m_aRWLock.readLocked ( () -> m_aCallbacks.isNotEmpty ());
  }

  @Nonnull
  public CallbackList  getClone ()
  {
    return m_aRWLock.readLocked ( () -> new CallbackList<> (this));
  }

  public void forEach (@Nonnull final Consumer  aConsumer)
  {
    for (final CALLBACKTYPE aCallback : getAllCallbacks ())
      try
      {
        aConsumer.accept (aCallback);
      }
      catch (final Throwable t)
      {
        s_aLogger.error ("Failed to invoke callback " + aCallback, t);
      }
  }

  @Nonnull
  public EContinue forEachWithReturn (@Nonnull final Function  aFunction)
  {
    for (final CALLBACKTYPE aCallback : getAllCallbacks ())
      try
      {
        if (aFunction.apply (aCallback).isBreak ())
          return EContinue.BREAK;
      }
      catch (final Throwable t)
      {
        s_aLogger.error ("Failed to invoke callback " + aCallback, t);
      }
    return EContinue.CONTINUE;
  }

  @Override
  public String toString ()
  {
    return new ToStringGenerator (this).append ("callbacks", m_aCallbacks).toString ();
  }
}