/*

 * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.

 */

/*

 * 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 com.sun.org.apache.xml.internal.utils;

import com.sun.org.apache.xalan.internal.utils.ObjectFactory;

import com.sun.org.apache.xml.internal.res.XMLErrorResources;

import com.sun.org.apache.xml.internal.res.XMLMessages;

import java.lang.reflect.InvocationTargetException;

import java.util.ArrayList;

import java.util.List;

/**

 * Pool of object of a given type to pick from to help memory usage

 * @xsl.usage internal

 * @LastModified: Oct 2017

 */

public class ObjectPool implements java.io.Serializable

{

    static final long serialVersionUID = -8519013691660936643L;

  /** Type of objects in this pool.

   *  @serial          */

  private final Class<?> objectType;

  /** Stack of given objects this points to.

   *  @serial          */

  private final List<Object> freeStack;

  /**

   * Constructor ObjectPool

   *

   * @param type Type of objects for this pool

   */

  public ObjectPool(Class<?> type)

  {

    objectType = type;

    freeStack = new ArrayList<>();

  }

  /**

   * Constructor ObjectPool

   *

   * @param className Fully qualified name of the type of objects for this pool.

   */

  public ObjectPool(String className)

  {

    try

    {

      objectType = ObjectFactory.findProviderClass(className, true);

    }

    catch(ClassNotFoundException cnfe)

    {

      throw new WrappedRuntimeException(cnfe);

    }

    freeStack = new ArrayList<>();

  }

  /**

   * Constructor ObjectPool

   *

   *

   * @param type Type of objects for this pool

   * @param size Size of vector to allocate

   */

  public ObjectPool(Class<?> type, int size)

  {

    objectType = type;

    freeStack = new ArrayList<>(size);

  }

  /**

   * Constructor ObjectPool

   *

   */

  public ObjectPool()

  {

    objectType = null;

    freeStack = new ArrayList<>();

  }

  /**

   * Get an instance of the given object in this pool if available

   *

   *

   * @return an instance of the given object if available or null

   */

  public synchronized Object getInstanceIfFree()

  {

    // Check if the pool is empty.

    if (!freeStack.isEmpty())

    {

      // Remove object from end of free pool.

      Object result = freeStack.remove(freeStack.size() - 1);

      return result;

    }

    return null;

  }

  /**

   * Get an instance of the given object in this pool

   *

   *

   * @return An instance of the given object

   */

  public synchronized Object getInstance()

  {

    // Check if the pool is empty.

    if (freeStack.isEmpty())

    {

      // Create a new object if so.

      try

      {

        return objectType.getConstructor().newInstance();

      }

      catch (InstantiationException | IllegalAccessException | SecurityException |

              IllegalArgumentException | InvocationTargetException | NoSuchMethodException ex){}

      // Throw unchecked exception for error in pool configuration.

      throw new RuntimeException(XMLMessages.createXMLMessage(

              XMLErrorResources.ER_EXCEPTION_CREATING_POOL, null));

    }

    else

    {

      // Remove object from end of free pool.

      Object result = freeStack.remove(freeStack.size() - 1);

      return result;

    }

  }

  /**

   * Add an instance of the given object to the pool

   *

   *

   * @param obj Object to add.

   */

  public synchronized void freeInstance(Object obj)

  {

    // Make sure the object is of the correct type.

    // Remove safety.  -sb

    // if (objectType.isInstance(obj))

    // {

    freeStack.add(obj);

    // }

    // else

    // {

    //  throw new IllegalArgumentException("argument type invalid for pool");

    // }

  }

}