/*

 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.util.logging;

/**

 * {@code Handler} that buffers requests in a circular buffer in memory.

 * <p>

 * Normally this {@code Handler} simply stores incoming {@code LogRecords}

 * into its memory buffer and discards earlier records.  This buffering

 * is very cheap and avoids formatting costs.  On certain trigger

 * conditions, the {@code MemoryHandler} will push out its current buffer

 * contents to a target {@code Handler}, which will typically publish

 * them to the outside world.

 * <p>

 * There are three main models for triggering a push of the buffer:

 * <ul>

 * <li>

 * An incoming {@code LogRecord} has a type that is greater than

 * a pre-defined level, the {@code pushLevel}. </li>

 * <li>

 * An external class calls the {@code push} method explicitly. </li>

 * <li>

 * A subclass overrides the {@code log} method and scans each incoming

 * {@code LogRecord} and calls {@code push} if a record matches some

 * desired criteria. </li>

 * </ul>

 * <p>

 * <b>Configuration:</b>

 * By default each {@code MemoryHandler} is initialized using the following

 * {@code LogManager} configuration properties where {@code <handler-name>}

 * refers to the fully-qualified class name of the handler.

 * If properties are not defined

 * (or have invalid values) then the specified default values are used.

 * If no default value is defined then a RuntimeException is thrown.

 * <ul>

 * <li>   &lt;handler-name&gt;.level

 *        specifies the level for the {@code Handler}

 *        (defaults to {@code Level.ALL}). </li>

 * <li>   &lt;handler-name&gt;.filter

 *        specifies the name of a {@code Filter} class to use

 *        (defaults to no {@code Filter}). </li>

 * <li>   &lt;handler-name&gt;.size

 *        defines the buffer size (defaults to 1000). </li>

 * <li>   &lt;handler-name&gt;.push

 *        defines the {@code pushLevel} (defaults to {@code level.SEVERE}). </li>

 * <li>   &lt;handler-name&gt;.target

 *        specifies the name of the target {@code Handler } class.

 *        (no default). </li>

 * </ul>

 * <p>

 * For example, the properties for {@code MemoryHandler} would be:

 * <ul>

 * <li>   java.util.logging.MemoryHandler.level=INFO </li>

 * <li>   java.util.logging.MemoryHandler.formatter=java.util.logging.SimpleFormatter </li>

 * </ul>

 * <p>

 * For a custom handler, e.g. com.foo.MyHandler, the properties would be:

 * <ul>

 * <li>   com.foo.MyHandler.level=INFO </li>

 * <li>   com.foo.MyHandler.formatter=java.util.logging.SimpleFormatter </li>

 * </ul>

 *

 * @since 1.4

 */

public class MemoryHandler extends Handler {

    private final static int DEFAULT_SIZE = 1000;

    private volatile Level pushLevel;

    private int size;

    private Handler target;

    private LogRecord buffer[];

    int start, count;

    /**

     * Create a {@code MemoryHandler} and configure it based on

     * {@code LogManager} configuration properties.

     */

    public MemoryHandler() {

        // configure with specific defaults for MemoryHandler

        super(Level.ALL, new SimpleFormatter(), null);

        LogManager manager = LogManager.getLogManager();

        String cname = getClass().getName();

        pushLevel = manager.getLevelProperty(cname +".push", Level.SEVERE);

        size = manager.getIntProperty(cname + ".size", DEFAULT_SIZE);

        if (size <= 0) {

            size = DEFAULT_SIZE;

        }

        String targetName = manager.getProperty(cname+".target");

        if (targetName == null) {

            throw new RuntimeException("The handler " + cname

                    + " does not specify a target");

        }

        Class<?> clz;

        try {

            clz = ClassLoader.getSystemClassLoader().loadClass(targetName);

            @SuppressWarnings("deprecation")

            Object o = clz.newInstance();

            target = (Handler) o;

        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {

            throw new RuntimeException("MemoryHandler can't load handler target \"" + targetName + "\"" , e);

        }

        init();

    }

    // Initialize.  Size is a count of LogRecords.

    private void init() {

        buffer = new LogRecord[size];

        start = 0;

        count = 0;

    }

    /**

     * Create a {@code MemoryHandler}.

     * <p>

     * The {@code MemoryHandler} is configured based on {@code LogManager}

     * properties (or their default values) except that the given {@code pushLevel}

     * argument and buffer size argument are used.

     *

     * @param target  the Handler to which to publish output.

     * @param size    the number of log records to buffer (must be greater than zero)

     * @param pushLevel  message level to push on

     *

     * @throws IllegalArgumentException if {@code size is <= 0}

     */

    public MemoryHandler(Handler target, int size, Level pushLevel) {

        // configure with specific defaults for MemoryHandler

        super(Level.ALL, new SimpleFormatter(), null);

        if (target == null || pushLevel == null) {

            throw new NullPointerException();

        }

        if (size <= 0) {

            throw new IllegalArgumentException();

        }

        this.target = target;

        this.pushLevel = pushLevel;

        this.size = size;

        init();

    }

    /**

     * Store a {@code LogRecord} in an internal buffer.

     * <p>

     * If there is a {@code Filter}, its {@code isLoggable}

     * method is called to check if the given log record is loggable.

     * If not we return.  Otherwise the given record is copied into

     * an internal circular buffer.  Then the record's level property is

     * compared with the {@code pushLevel}. If the given level is

     * greater than or equal to the {@code pushLevel} then {@code push}

     * is called to write all buffered records to the target output

     * {@code Handler}.

     *

     * @param  record  description of the log event. A null record is

     *                 silently ignored and is not published

     */

    @Override

    public synchronized void publish(LogRecord record) {

        if (!isLoggable(record)) {

            return;

        }

        int ix = (start+count)%buffer.length;

        buffer[ix] = record;

        if (count < buffer.length) {

            count++;

        } else {

            start++;

            start %= buffer.length;

        }

        if (record.getLevel().intValue() >= pushLevel.intValue()) {

            push();

        }

    }

    /**

     * Push any buffered output to the target {@code Handler}.

     * <p>

     * The buffer is then cleared.

     */

    public synchronized void push() {

        for (int i = 0; i < count; i++) {

            int ix = (start+i)%buffer.length;

            LogRecord record = buffer[ix];

            target.publish(record);

        }

        // Empty the buffer.

        start = 0;

        count = 0;

    }

    /**

     * Causes a flush on the target {@code Handler}.

     * <p>

     * Note that the current contents of the {@code MemoryHandler}

     * buffer are <b>not</b> written out.  That requires a "push".

     */

    @Override

    public void flush() {

        target.flush();

    }

    /**

     * Close the {@code Handler} and free all associated resources.

     * This will also close the target {@code Handler}.

     *

     * @exception  SecurityException  if a security manager exists and if

     *             the caller does not have {@code LoggingPermission("control")}.

     */

    @Override

    public void close() throws SecurityException {

        target.close();

        setLevel(Level.OFF);

    }

    /**

     * Set the {@code pushLevel}.  After a {@code LogRecord} is copied

     * into our internal buffer, if its level is greater than or equal to

     * the {@code pushLevel}, then {@code push} will be called.

     *

     * @param newLevel the new value of the {@code pushLevel}

     * @exception  SecurityException  if a security manager exists and if

     *             the caller does not have {@code LoggingPermission("control")}.

     */

    public synchronized void setPushLevel(Level newLevel) throws SecurityException {

        if (newLevel == null) {

            throw new NullPointerException();

        }

        checkPermission();

        pushLevel = newLevel;

    }

    /**

     * Get the {@code pushLevel}.

     *

     * @return the value of the {@code pushLevel}

     */

    public Level getPushLevel() {

        return pushLevel;

    }

    /**

     * Check if this {@code Handler} would actually log a given

     * {@code LogRecord} into its internal buffer.

     * <p>

     * This method checks if the {@code LogRecord} has an appropriate level and

     * whether it satisfies any {@code Filter}.  However it does <b>not</b>

     * check whether the {@code LogRecord} would result in a "push" of the

     * buffer contents. It will return false if the {@code LogRecord} is null.

     *

     * @param record  a {@code LogRecord}

     * @return true if the {@code LogRecord} would be logged.

     *

     */

    @Override

    public boolean isLoggable(LogRecord record) {

        return super.isLoggable(record);

    }

}