<?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

 */

/**

 * Users should extend this class to implement customized logging

 * event filtering. Note that {@link LoggerCategory} and {@link LoggerAppender},

 * the parent class of all standard

 * appenders, have built-in filtering rules. It is suggested that you

 * first use and understand the built-in rules before rushing to write

 * your own custom filters.

 *

 * <p>This abstract class assumes and also imposes that filters be

 * organized in a linear chain. The {@link #decide

 * decide(LoggerLoggingEvent)} method of each filter is called sequentially,

 * in the order of their addition to the chain.

 *

 * <p>The {@link decide()} method must return one

 * of the integer constants {@link LoggerFilter::DENY},

 * {@link LoggerFilter::NEUTRAL} or {@link LoggerFilter::ACCEPT}.

 *

 * <p>If the value {@link LoggerFilter::DENY} is returned, then the log event is

 * dropped immediately without consulting with the remaining

 * filters.

 *

 * <p>If the value {@link LoggerFilter::NEUTRAL} is returned, then the next filter

 * in the chain is consulted. If there are no more filters in the

 * chain, then the log event is logged. Thus, in the presence of no

 * filters, the default behaviour is to log all logging events.

 *

 * <p>If the value {@link LoggerFilter::ACCEPT} is returned, then the log

 * event is logged without consulting the remaining filters.

 *

 * <p>The philosophy of log4php filters is largely inspired from the

 * Linux ipchains.

 *

 * @version $Revision: 1213283 $

 * @package log4php

 */

abstract class LoggerFilter extends LoggerConfigurable {

    /**

     * The log event must be logged immediately without consulting with

     * the remaining filters, if any, in the chain.

     */

    const ACCEPT = 1;

    /**

     * This filter is neutral with respect to the log event. The

     * remaining filters, if any, should be consulted for a final decision.

     */

    const NEUTRAL = 0;

    /**

     * The log event must be dropped immediately without consulting

     * with the remaining filters, if any, in the chain.

     */

    const DENY = -1;

    /**

     * @var LoggerFilter Points to the next {@link LoggerFilter} in the filter chain.

     */

    protected $next;

    /**

     * Usually filters options become active when set. We provide a

     * default do-nothing implementation for convenience.

     */

    public function activateOptions() {

    }

    /**

     * Decide what to do.

     * <p>If the decision is {@link LoggerFilter::DENY}, then the event will be

     * dropped. If the decision is {@link LoggerFilter::NEUTRAL}, then the next

     * filter, if any, will be invoked. If the decision is {@link LoggerFilter::ACCEPT} then

     * the event will be logged without consulting with other filters in

     * the chain.

     *

     * @param LoggerLoggingEvent $event The {@link LoggerLoggingEvent} to decide upon.

     * @return integer {@link LoggerFilter::NEUTRAL} or {@link LoggerFilter::DENY}|{@link LoggerFilter::ACCEPT}

     */

    public function decide(LoggerLoggingEvent $event) {

        return self::NEUTRAL;

    }

    /**

     * Adds a new filter to the filter chain this filter is a part of.

     * If this filter has already and follow up filter, the param filter

     * is passed on until it is the last filter in chain.

     *

     * @param $filter - the filter to add to this chain

     */

    public function addNext($filter) {

        if ($this->next !== null) {

            $this->next->addNext($filter);

        } else {

            $this->next = $filter;

        }

    }

    /**

     * Returns the next filter in this chain

     * @return the next filter

     */

    public function getNext() {

        return $this->next;

    }

}