/*
 * Copyright (c) 2003, KNOPFLERFISH project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials
 *   provided with the distribution.
 *
 * - Neither the name of the KNOPFLERFISH project nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.knopflerfish.util;


/**
 * An object with a timeout.
 *
 * <p>
 * A CachedObject has a timeout period -
 * during that period the <code>get</code> method will return the
 * stored object, afterwards <code>get</code> will return
 * <code>null</code>
 * </p>
 *
 * @see CacheMap
 */
public class CachedObject {

  /**
   * Default timeout period in milliseconds. Value is 60 seconds.
   */
  public final static long DEFAULT_TIMEOUT = 60 * 1000;

  // Timeout in milliseconds for this cached object
  private long timeout;

  // Creation time of this cached object.
  private long creationTime;

  // Actual object stored in cache
  private Object object;

  /**
   * Equivalent to <code>CachedObject(null)</code>.
   * 
   * @see CacheMap
   */
  public CachedObject() {
    this(null);
  }

  /**
   * Equivalent to <code>CachedObject(object, CachedObject.DEFAULT_TIMEOUT)</code>
   * 
   * @see #DEFAULT_TIMEOUT
   */
  public CachedObject(Object object) {
    this(object, DEFAULT_TIMEOUT);
  }

  /**
   * Create a cached object from an object and a specified timeout.
   *
   * @param object  Object to cache
   * @param timeout period in milliseconds.
   * @see #DEFAULT_TIMEOUT
   */
  public CachedObject(Object object, long timeout) {
    this.timeout = timeout;
    set(object);
  }

  /**
   * Set the cache's object and restore its creation time.
   *
   * @param object Object to cache
   */
  public void set(Object object) {
    this.object = object;
    creationTime = System.currentTimeMillis();
  }

  /**
   * Get the cached object.
   *
   * @return The cached object before its timeout period, <code>null</code>
   *         afterwards.
   */
  public Object get() {

    long now = System.currentTimeMillis();
    if (now - creationTime > timeout) {
      flush();
    }

    return object;
  }

  /**
   * Clear the stored object. After this call, <code>get</code> will
   *
   */
  public void flush() {
    object = null;
  }

  /**
   * Print the cached object as
   * "&lt;object's string value&gt;:&lt;remaining time in milliseconds&gt;"
   */
  public String toString() {
    return object.toString() + ":" + (System.currentTimeMillis() - creationTime);
  }

} // CachedObject