/*
 * 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.
 */

// Contibutors:  Aaron Greenhouse <aarong@cs.cmu.edu>
//               Thomas Tuft Muller <ttm@online.no>
package org.apache.log4j;

import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.apache.log4j.helpers.AppenderAttachableImpl;
import org.apache.log4j.spi.AppenderAttachable;
import org.apache.log4j.spi.LoggingEvent;

/**
 * The AsyncAppender lets users log events asynchronously.
 * <p/>
 * <p/>
 * The AsyncAppender will collect the events sent to it and then dispatch them to all the appenders that are attached to
 * it. You can attach multiple appenders to an AsyncAppender.
 * </p>
 * <p/>
 * <p/>
 * The AsyncAppender uses a separate thread to serve the events in its buffer.
 * </p>
 * <p/>
 * <b>Important note:</b> The <code>AsyncAppender</code> can only be script
 * configured using the {@link org.apache.log4j.xml.DOMConfigurator}.
 * </p>
 *
 * @author Ceki G&uuml;lc&uuml;
 * @author Curt Arnold
 * @since 0.9.1
 */
public class AsyncAppender extends AppenderSkeleton implements AppenderAttachable {
    /**
     * The default buffer size is set to 128 events.
     */
    public static final int DEFAULT_BUFFER_SIZE = 128;

    /**
     * Event buffer, also used as monitor to protect itself and discardMap from simulatenous modifications.
     */
    private final List buffer = new ArrayList();

    /**
     * Map of DiscardSummary objects keyed by logger name.
     */
    private final Map discardMap = new HashMap();

    /**
     * Buffer size.
     */
    private int bufferSize = DEFAULT_BUFFER_SIZE;

    /**
     * Nested appenders.
     */
    AppenderAttachableImpl aai;

    /**
     * Nested appenders.
     */
    private final AppenderAttachableImpl appenders;

    /**
     * Dispatcher.
     */
    private final Thread dispatcher;

    /**
     * Should location info be included in dispatched messages.
     */
    private boolean locationInfo = false;

    /**
     * Does appender block when buffer is full.
     */
    private boolean blocking = true;

    /**
     * Create new instance.
     */
    public AsyncAppender() {
        appenders = new AppenderAttachableImpl();

        //
        // only set for compatibility
        aai = appenders;

        dispatcher = new Thread(new Dispatcher(this, buffer, discardMap, appenders));

        // It is the user's responsibility to close appenders before
        // exiting.
        dispatcher.setDaemon(true);

        // set the dispatcher priority to lowest possible value
        // dispatcher.setPriority(Thread.MIN_PRIORITY);
        dispatcher.setName("AsyncAppender-Dispatcher-" + dispatcher.getName());
        dispatcher.start();
    }

    /**
     * Add appender.
     *
     * @param newAppender appender to add, may not be null.
     */
    public void addAppender(final Appender newAppender) {
        synchronized (appenders) {
            appenders.addAppender(newAppender);
        }
    }

    /**
     * {@inheritDoc}
     */
    public void append(final LoggingEvent event) {
        //
        // if dispatcher thread has died then
        // append subsequent events synchronously
        // See bug 23021
        if ((dispatcher == null) || !dispatcher.isAlive() || (bufferSize <= 0)) {
            synchronized (appenders) {
                appenders.appendLoopOnAppenders(event);
            }

            return;
        }

        // Set the NDC and thread name for the calling thread as these
        // LoggingEvent fields were not set at event creation time.
        event.getNDC();
        event.getThreadName();
        // Get a copy of this thread's MDC.
        event.getMDCCopy();
        if (locationInfo) {
            event.getLocationInformation();
        }
        event.getRenderedMessage();
        event.getThrowableStrRep();

        synchronized (buffer) {
            while (true) {
                int previousSize = buffer.size();

                if (previousSize < bufferSize) {
                    buffer.add(event);

                    //
                    // if buffer had been empty
                    // signal all threads waiting on buffer
                    // to check their conditions.
                    //
                    if (previousSize == 0) {
                        buffer.notifyAll();
                    }

                    break;
                }

                //
                // Following code is only reachable if buffer is full
                //
                //
                // if blocking and thread is not already interrupted
                // and not the dispatcher then
                // wait for a buffer notification
                boolean discard = true;
                if (blocking && !Thread.interrupted() && Thread.currentThread() != dispatcher) {
                    try {
                        buffer.wait();
                        discard = false;
                    } catch (InterruptedException e) {
                        //
                        // reset interrupt status so
                        // calling code can see interrupt on
                        // their next wait or sleep.
                        Thread.currentThread().interrupt();
                    }
                }

                //
                // if blocking is false or thread has been interrupted
                // add event to discard map.
                //
                if (discard) {
                    String loggerName = event.getLoggerName();
                    DiscardSummary summary = (DiscardSummary) discardMap.get(loggerName);

                    if (summary == null) {
                        summary = new DiscardSummary(event);
                        discardMap.put(loggerName, summary);
                    } else {
                        summary.add(event);
                    }

                    break;
                }
            }
        }
    }

    /**
     * Close this <code>AsyncAppender</code> by interrupting the dispatcher thread which will process all pending events
     * before exiting.
     */
    public void close() {
        /**
         * Set closed flag and notify all threads to check their conditions. Should
         * result in dispatcher terminating.
         */
        synchronized (buffer) {
            closed = true;
            buffer.notifyAll();
        }

        try {
            dispatcher.join();
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            org.apache.log4j.helpers.LogLog.error(
                    "Got an InterruptedException while waiting for the " + "dispatcher to finish.", e);
        }

        //
        // close all attached appenders.
        //
        synchronized (appenders) {
            Enumeration iter = appenders.getAllAppenders();

            if (iter != null) {
                while (iter.hasMoreElements()) {
                    Object next = iter.nextElement();

                    if (next instanceof Appender) {
                        ((Appender) next).close();
                    }
                }
            }
        }
    }

    /**
     * Get iterator over attached appenders.
     *
     * @return iterator or null if no attached appenders.
     */
    public Enumeration getAllAppenders() {
        synchronized (appenders) {
            return appenders.getAllAppenders();
        }
    }

    /**
     * Get appender by name.
     *
     * @param name name, may not be null.
     * @return matching appender or null.
     */
    public Appender getAppender(final String name) {
        synchronized (appenders) {
            return appenders.getAppender(name);
        }
    }

    /**
     * Gets whether the location of the logging request call should be captured.
     *
     * @return the current value of the <b>LocationInfo</b> option.
     */
    public boolean getLocationInfo() {
        return locationInfo;
    }

    /**
     * Determines if specified appender is attached.
     *
     * @param appender appender.
     * @return true if attached.
     */
    public boolean isAttached(final Appender appender) {
        synchronized (appenders) {
            return appenders.isAttached(appender);
        }
    }

    /**
     * {@inheritDoc}
     */
    public boolean requiresLayout() {
        return false;
    }

    /**
     * Removes and closes all attached appenders.
     */
    public void removeAllAppenders() {
        synchronized (appenders) {
            appenders.removeAllAppenders();
        }
    }

    /**
     * Removes an appender.
     *
     * @param appender appender to remove.
     */
    public void removeAppender(final Appender appender) {
        synchronized (appenders) {
            appenders.removeAppender(appender);
        }
    }

    /**
     * Remove appender by name.
     *
     * @param name name.
     */
    public void removeAppender(final String name) {
        synchronized (appenders) {
            appenders.removeAppender(name);
        }
    }

    /**
     * The <b>LocationInfo</b> option takes a boolean value. By default, it is set to false which means there will be no
     * effort to extract the location information related to the event. As a result, the event that will be ultimately
     * logged will likely to contain the wrong location information (if present in the log format).
     * <p/>
     * <p/>
     * Location information extraction is comparatively very slow and should be avoided unless performance is not a
     * concern.
     * </p>
     *
     * @param flag true if location information should be extracted.
     */
    public void setLocationInfo(final boolean flag) {
        locationInfo = flag;
    }

    /**
     * Sets the number of messages allowed in the event buffer before the calling thread is blocked (if blocking is
     * true) or until messages are summarized and discarded. Changing the size will not affect messages already in the
     * buffer.
     *
     * @param size buffer size, must be positive.
     */
    public void setBufferSize(final int size) {
        //
        // log4j 1.2 would throw exception if size was negative
        // and deadlock if size was zero.
        //
        if (size < 0) {
            throw new java.lang.NegativeArraySizeException("size");
        }

        synchronized (buffer) {
            //
            // don't let size be zero.
            //
            bufferSize = (size < 1) ? 1 : size;
            buffer.notifyAll();
        }
    }

    /**
     * Gets the current buffer size.
     *
     * @return the current value of the <b>BufferSize</b> option.
     */
    public int getBufferSize() {
        return bufferSize;
    }

    /**
     * Sets whether appender should wait if there is no space available in the event buffer or immediately return.
     *
     * @param value true if appender should wait until available space in buffer.
     * @since 1.2.14
     */
    public void setBlocking(final boolean value) {
        synchronized (buffer) {
            blocking = value;
            buffer.notifyAll();
        }
    }

    /**
     * Gets whether appender should block calling thread when buffer is full. If false, messages will be counted by
     * logger and a summary message appended after the contents of the buffer have been appended.
     *
     * @return true if calling thread will be blocked when buffer is full.
     * @since 1.2.14
     */
    public boolean getBlocking() {
        return blocking;
    }

    /**
     * Summary of discarded logging events for a logger.
     */
    private static final class DiscardSummary {
        /**
         * First event of the highest severity.
         */
        private LoggingEvent maxEvent;

        /**
         * Total count of messages discarded.
         */
        private int count;

        /**
         * Create new instance.
         *
         * @param event event, may not be null.
         */
        public DiscardSummary(final LoggingEvent event) {
            maxEvent = event;
            count = 1;
        }

        /**
         * Add discarded event to summary.
         *
         * @param event event, may not be null.
         */
        public void add(final LoggingEvent event) {
            if (event.getLevel().toInt() > maxEvent.getLevel().toInt()) {
                maxEvent = event;
            }

            count++;
        }

        /**
         * Create event with summary information.
         *
         * @return new event.
         */
        public LoggingEvent createEvent() {
            String msg = MessageFormat.format("Discarded {0} messages due to full event buffer including: {1}",
                    new Object[] { new Integer(count), maxEvent.getMessage() });

            return new LoggingEvent("org.apache.log4j.AsyncAppender.DONT_REPORT_LOCATION",
                    Logger.getLogger(maxEvent.getLoggerName()), maxEvent.getLevel(), msg, null);
        }
    }

    /**
     * Event dispatcher.
     */
    private static class Dispatcher implements Runnable {
        /**
         * Parent AsyncAppender.
         */
        private final AsyncAppender parent;

        /**
         * Event buffer.
         */
        private final List buffer;

        /**
         * Map of DiscardSummary keyed by logger name.
         */
        private final Map discardMap;

        /**
         * Wrapped appenders.
         */
        private final AppenderAttachableImpl appenders;

        /**
         * Create new instance of dispatcher.
         *
         * @param parent     parent AsyncAppender, may not be null.
         * @param buffer     event buffer, may not be null.
         * @param discardMap discard map, may not be null.
         * @param appenders  appenders, may not be null.
         */
        public Dispatcher(final AsyncAppender parent, final List buffer, final Map discardMap,
                final AppenderAttachableImpl appenders) {

            this.parent = parent;
            this.buffer = buffer;
            this.appenders = appenders;
            this.discardMap = discardMap;
        }

        /**
         * {@inheritDoc}
         */
        public void run() {
            boolean isActive = true;

            //
            // if interrupted (unlikely), end thread
            //
            try {
                //
                // loop until the AsyncAppender is closed.
                //
                while (isActive) {
                    LoggingEvent[] events = null;

                    //
                    // extract pending events while synchronized
                    // on buffer
                    //
                    synchronized (buffer) {
                        int bufferSize = buffer.size();
                        isActive = !parent.closed;

                        while ((bufferSize == 0) && isActive) {
                            buffer.wait();
                            bufferSize = buffer.size();
                            isActive = !parent.closed;
                        }

                        if (bufferSize > 0) {
                            events = new LoggingEvent[bufferSize + discardMap.size()];
                            buffer.toArray(events);

                            //
                            // add events due to buffer overflow
                            //
                            int index = bufferSize;

                            for (Iterator iter = discardMap.values().iterator(); iter.hasNext(); ) {
                                events[index++] = ((DiscardSummary) iter.next()).createEvent();
                            }

                            //
                            // clear buffer and discard map
                            //
                            buffer.clear();
                            discardMap.clear();

                            //
                            // allow blocked appends to continue
                            buffer.notifyAll();
                        }
                    }

                    //
                    // process events after lock on buffer is released.
                    //
                    if (events != null) {
                        for (int i = 0; i < events.length; i++) {
                            synchronized (appenders) {
                                appenders.appendLoopOnAppenders(events[i]);
                            }
                        }
                    }
                }
            } catch (InterruptedException ex) {
                Thread.currentThread().interrupt();
            }
        }
    }
}
