/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2013, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core;

import ch.qos.logback.core.spi.AppenderAttachable;
import ch.qos.logback.core.spi.AppenderAttachableImpl;

import java.util.Iterator;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

/**
 * This appender and derived classes, log events asynchronously.  In order to avoid loss of logging events, this
 * appender should be closed. It is the user's  responsibility to close appenders, typically at the end of the
 * application lifecycle.
 * <p/>
 * This appender buffers events in a {@link BlockingQueue}. {@link Worker} thread created by this appender takes
 * events from the head of the queue, and dispatches them to the single appender attached to this appender.
 * <p/>
 * <p>Please refer to the <a href="http://logback.qos.ch/manual/appenders.html#AsyncAppender">logback manual</a> for
 * further information about this appender.</p>
 *
 * @param <E>
 * @author Ceki G&uuml;lc&uuml;
 * @author Torsten Juergeleit
 * @since 1.0.4
 */
public class AsyncAppenderBase<E> extends UnsynchronizedAppenderBase<E> implements AppenderAttachable<E> {

  AppenderAttachableImpl<E> aai = new AppenderAttachableImpl<E>();
  BlockingQueue<E> blockingQueue;

  /**
   * The default buffer size.
   */
  public static final int DEFAULT_QUEUE_SIZE = 256;
  int queueSize = DEFAULT_QUEUE_SIZE;

  int appenderCount = 0;

  static final int UNDEFINED = -1;
  int discardingThreshold = UNDEFINED;

  Worker worker = new Worker();

  /**
   * Is the eventObject passed as parameter discardable? The base class's implementation of this method always returns
   * 'false' but sub-classes may (and do) override this method.
   * <p/>
   * <p>Note that only if the buffer is nearly full are events discarded. Otherwise, when the buffer is "not full"
   * all events are logged.
   *
   * @param eventObject
   * @return - true if the event can be discarded, false otherwise
   */
  protected boolean isDiscardable(E eventObject) {
    return false;
  }


  /**
   * Pre-process the event prior to queueing. The base class does no pre-processing but sub-classes can
   * override this behavior.
   *
   * @param eventObject
   */
  protected void preprocess(E eventObject) {
  }


  @Override
  public void start() {
    if (appenderCount == 0) {
      addError("No attached appenders found.");
      return;
    }
    if (queueSize < 1) {
      addError("Invalid queue size [" + queueSize + "]");
      return;
    }
    blockingQueue = new ArrayBlockingQueue<E>(queueSize);

    if (discardingThreshold == UNDEFINED)
      discardingThreshold = queueSize / 5;
    addInfo("Setting discardingThreshold to " + discardingThreshold);
    worker.setDaemon(true);
    worker.setName("AsyncAppender-Worker-" + worker.getName());
    // make sure this instance is marked as "started" before staring the worker Thread
    super.start();
    worker.start();
  }

  @Override
  public void stop() {
    if (!isStarted())
      return;

    // mark this appender as stopped so that Worker can also processPriorToRemoval if it is invoking aii.appendLoopOnAppenders
    // and sub-appenders consume the interruption
    super.stop();

    // interrupt the worker thread so that it can terminate. Note that the interruption can be consumed
    // by sub-appenders
    worker.interrupt();
    try {
      worker.join(1000);
    } catch (InterruptedException e) {
      addError("Failed to join worker thread", e);
    }
  }


  @Override
  protected void append(E eventObject) {
    if (isQueueBelowDiscardingThreshold() && isDiscardable(eventObject)) {
      return;
    }
    preprocess(eventObject);
    put(eventObject);
  }

  private boolean isQueueBelowDiscardingThreshold() {
    return (blockingQueue.remainingCapacity() < discardingThreshold);
  }

  private void put(E eventObject) {
    try {
      blockingQueue.put(eventObject);
    } catch (InterruptedException e) {
    }
  }

  public int getQueueSize() {
    return queueSize;
  }

  public void setQueueSize(int queueSize) {
    this.queueSize = queueSize;
  }

  public int getDiscardingThreshold() {
    return discardingThreshold;
  }

  public void setDiscardingThreshold(int discardingThreshold) {
    this.discardingThreshold = discardingThreshold;
  }

  /**
   * Returns the number of elements currently in the blocking queue.
   *
   * @return number of elements currently in the queue.
   */
  public int getNumberOfElementsInQueue() {
    return blockingQueue.size();
  }

  /**
   * The remaining capacity available in the blocking queue.
   *
   * @return the remaining capacity
   * @see {@link java.util.concurrent.BlockingQueue#remainingCapacity()}
   */
  public int getRemainingCapacity() {
    return blockingQueue.remainingCapacity();
  }



  public void addAppender(Appender<E> newAppender) {
    if (appenderCount == 0) {
      appenderCount++;
      addInfo("Attaching appender named ["+newAppender.getName()+"] to AsyncAppender.");
      aai.addAppender(newAppender);
    } else {
      addWarn("One and only one appender may be attached to AsyncAppender.");
      addWarn("Ignoring additional appender named [" + newAppender.getName() + "]");
    }
  }

  public Iterator<Appender<E>> iteratorForAppenders() {
    return aai.iteratorForAppenders();
  }

  public Appender<E> getAppender(String name) {
    return aai.getAppender(name);
  }

  public boolean isAttached(Appender<E> eAppender) {
    return aai.isAttached(eAppender);
  }

  public void detachAndStopAllAppenders() {
    aai.detachAndStopAllAppenders();
  }

  public boolean detachAppender(Appender<E> eAppender) {
    return aai.detachAppender(eAppender);
  }

  public boolean detachAppender(String name) {
    return aai.detachAppender(name);
  }

  class Worker extends Thread {

    public void run() {
      AsyncAppenderBase<E> parent = AsyncAppenderBase.this;
      AppenderAttachableImpl<E> aai = parent.aai;

      // loop while the parent is started
      while (parent.isStarted()) {
        try {
          E e = parent.blockingQueue.take();
          aai.appendLoopOnAppenders(e);
        } catch (InterruptedException ie) {
          break;
        }
      }

      addInfo("Worker thread will flush remaining events before exiting. ");
      for (E e : parent.blockingQueue) {
        aai.appendLoopOnAppenders(e);
      }

      aai.detachAndStopAllAppenders();
    }
  }
}
