/*
 * 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.bundle.log;

import java.util.*;
import org.osgi.framework.*;
import org.osgi.service.log.*;

/**
 ** A LogReaderServiceImpl keeps track of the log subscribes from one
 ** BundleContext. It also contains a reference to the
 ** LogReaderServiceFactory, where the log functionality is
 ** implemented.
 **
 ** The log function in registered LogListeners are called when the
 ** LogReaderServiceFactory calls the callback method.
 **/
public class LogReaderServiceImpl
  implements LogReaderService
{

  /** The log reader service factory that implements the log functionlity.*/
  LogReaderServiceFactory lrsf;

  /**
   ** A Vector with LogListener objects.
   **/
  Vector listeners = new Vector( 2 );

  /**
   ** The constructor saves the LogReaderServiceFactory.
   ** @param lrsf the log reader service factory that implements the
   **        log functionlity.
   **/
  LogReaderServiceImpl(LogReaderServiceFactory lrsf) {
    this.lrsf = lrsf;
  }


  /**
   ** Subscribe method.
   ** @param l A log listener to be notify when new log entries arrives.
   **/
  public synchronized void addLogListener(LogListener l) {
    if(l==null)
      throw new IllegalArgumentException("LogListener can not be null");
    if( !listeners.contains( l ) ) {
      listeners.addElement(l);
    }
  }


  /**
   ** Unsubscribe method.
   ** LogListeners are removed when number of subscriptions are 0.
   ** @param l A log listener to be removed.
   **/
  public synchronized void removeLogListener(LogListener l) {
    if(l==null)
      throw new IllegalArgumentException("LogListener can not be null");
    listeners.removeElement(l);
  }

  /**
   ** Bridge to LogReaderServiceFactory for fetching the log.
   **/
  public Enumeration getLog() {
    return lrsf.getLog();
  }

  /**
   ** Used by LogReaderServiceFactory for every new log entry.
   **
   ** Note that the callback operation is not disturbed by changes in
   ** the listener set since such changes will result in that
   ** <code>listerners</code> refers to a new object, but the callback
   ** operation will continue its enumeration of the old listeners
   ** object.
   **
   ** @param le A log entry to send to all listeners.
   **/
  public void callback(LogEntry le) {
    Enumeration i = listeners.elements();

    while(i.hasMoreElements()) {
      try {
	((LogListener)i.nextElement()).logged(le);
      } catch (Exception exc) {
      }
    }
  }

}