<?php

/**

 * 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.

 *

 * @package log4php

 */

/**

 * The NDC class implements <i>nested diagnostic contexts</i>.

 *

 * NDC was defined by Neil Harrison in the article "Patterns for Logging

 * Diagnostic Messages" part of the book <i>"Pattern Languages of

 * Program Design 3"</i> edited by Martin et al.

 *

 * A Nested Diagnostic Context, or NDC in short, is an instrument

 * to distinguish interleaved log output from different sources. Log

 * output is typically interleaved when a server handles multiple

 * clients near-simultaneously.

 *

 * This class is similar to the {@link LoggerMDC} class except that it is

 * based on a stack instead of a map.

 *

 * Interleaved log output can still be meaningful if each log entry

 * from different contexts had a distinctive stamp. This is where NDCs

 * come into play.

 *

 * <b>Note that NDCs are managed on a per thread basis</b>.

 *

 * NDC operations such as {@link push()}, {@link pop()},

 * {@link clear()}, {@link getDepth()} and {@link setMaxDepth()}

 * affect the NDC of the <i>current</i> thread only. NDCs of other

 * threads remain unaffected.

 *

 * For example, a servlet can build a per client request NDC

 * consisting the clients host name and other information contained in

 * the the request. <i>Cookies</i> are another source of distinctive

 * information. To build an NDC one uses the {@link push()}

 * operation.

 *

 * Simply put,

 *

 * - Contexts can be nested.

 * - When entering a context, call <kbd>LoggerNDC::push()</kbd>

 *     As a side effect, if there is no nested diagnostic context for the

 *     current thread, this method will create it.

 * - When leaving a context, call <kbd>LoggerNDC::pop()</kbd>

 * - <b>When exiting a thread make sure to call {@link remove()}</b>

 *

 * There is no penalty for forgetting to match each

 * <kbd>push</kbd> operation with a corresponding <kbd>pop</kbd>,

 * except the obvious mismatch between the real application context

 * and the context set in the NDC.

 *

 * If configured to do so, {@link LoggerPatternLayout} and {@link LoggerLayoutTTCC}

 * instances automatically retrieve the nested diagnostic

 * context for the current thread without any user intervention.

 * Hence, even if a servlet is serving multiple clients

 * simultaneously, the logs emanating from the same code (belonging to

 * the same category) can still be distinguished because each client

 * request will have a different NDC tag.

 *

 * Example:

 *

 * {@example ../../examples/php/ndc.php 19}<br>

 *

 * With the properties file:

 *

 * {@example ../../examples/resources/ndc.properties 18}<br>

 *

 * Will result in the following (notice the conn and client ids):

 *

 * <pre>

 * 2009-09-13 19:04:27 DEBUG root conn=1234: just received a new connection in src/examples/php/ndc.php at 23

 * 2009-09-13 19:04:27 DEBUG root conn=1234 client=ab23: some more messages that can in src/examples/php/ndc.php at 25

 * 2009-09-13 19:04:27 DEBUG root conn=1234 client=ab23: now related to a client in src/examples/php/ndc.php at 26

 * 2009-09-13 19:04:27 DEBUG root : back and waiting for new connections in src/examples/php/ndc.php at 29

 * </pre>

 *

 * @version $Revision: 1350602 $

 * @package log4php

 * @since 0.3

 */

class LoggerNDC {

    /** This is the repository of NDC stack */

    private static $stack = array();

    /**

     * Clear any nested diagnostic information if any. This method is

     * useful in cases where the same thread can be potentially used

     * over and over in different unrelated contexts.

     *

     * <p>This method is equivalent to calling the {@link setMaxDepth()}

     * method with a zero <var>maxDepth</var> argument.

     */

    public static function clear() {

        self::$stack = array();

    }

    /**

     * Never use this method directly, use the {@link LoggerLoggingEvent::getNDC()} method instead.

     * @return array

     */

    public static function get() {

        return implode(' ', self::$stack);

    }

    /**

     * Get the current nesting depth of this diagnostic context.

     *

     * @see setMaxDepth()

     * @return integer

     */

    public static function getDepth() {

        return count(self::$stack);

    }

    /**

     * Clients should call this method before leaving a diagnostic

     * context.

     *

     * <p>The returned value is the value that was pushed last. If no

     * context is available, then the empty string "" is returned.</p>

     *

     * @return string The innermost diagnostic context.

     */

    public static function pop() {

        if (count(self::$stack) > 0) {

            return array_pop(self::$stack);

        } else {

            return '';

        }

    }

    /**

     * Looks at the last diagnostic context at the top of this NDC

     * without removing it.

     *

     * <p>The returned value is the value that was pushed last. If no

     * context is available, then the empty string "" is returned.</p>

     * @return string The innermost diagnostic context.

     */

    public static function peek() {

        if (count(self::$stack) > 0) {

            return end(self::$stack);

        } else {

            return '';

        }

    }

    /**

     * Push new diagnostic context information for the current thread.

     *

     * <p>The contents of the <var>message</var> parameter is

     * determined solely by the client.

     *

     * @param string $message The new diagnostic context information.

     */

    public static function push($message) {

        array_push(self::$stack, (string)$message);

    }

    /**

     * Remove the diagnostic context for this thread.

     */

    public static function remove() {

        LoggerNDC::clear();

    }

    /**

     * Set maximum depth of this diagnostic context. If the current

     * depth is smaller or equal to <var>maxDepth</var>, then no

     * action is taken.

     *

     * <p>This method is a convenient alternative to multiple

     * {@link pop()} calls. Moreover, it is often the case that at

     * the end of complex call sequences, the depth of the NDC is

     * unpredictable. The {@link setMaxDepth()} method circumvents

     * this problem.

     *

     * @param integer $maxDepth

     * @see getDepth()

     */

    public static function setMaxDepth($maxDepth) {

        $maxDepth = (int)$maxDepth;

        if (LoggerNDC::getDepth() > $maxDepth) {

            self::$stack = array_slice(self::$stack, 0, $maxDepth);

        }

    }

}