/*
    * 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 org.apache.logging.log4j.core.filter;
  
  import java.util.Queue;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.DelayQueue;
  import java.util.concurrent.Delayed;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.logging.log4j.Level;
  import org.apache.logging.log4j.Marker;
  import org.apache.logging.log4j.core.Filter;
  import org.apache.logging.log4j.core.LogEvent;
  import org.apache.logging.log4j.core.Logger;
  import org.apache.logging.log4j.core.config.Node;
  import org.apache.logging.log4j.core.config.plugins.Plugin;
  import org.apache.logging.log4j.core.config.plugins.PluginBuilderAttribute;
  import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
  import org.apache.logging.log4j.message.Message;
  
  /**
   * The <code>BurstFilter</code> is a logging filter that regulates logging traffic.
   * 
   * <p>
   * Use this filter when you want to control the maximum burst of log statements that can be sent to an appender. The
   * filter is configured in the log4j configuration file. For example, the following configuration limits the number of
   * INFO level (as well as DEBUG and TRACE) log statements that can be sent to the console to a burst of 100 with an
   * average rate of 16 per second. WARN, ERROR and FATAL messages would continue to be delivered.
   * </p>
   * <code>
   * &lt;Console name="console"&gt;<br>
   * &nbsp;&lt;PatternLayout pattern="%-5p %d{dd-MMM-yyyy HH:mm:ss} %x %t %m%n"/&gt;<br>
   * &nbsp;&lt;filters&gt;<br>
   * &nbsp;&nbsp;&lt;Burst level="INFO" rate="16" maxBurst="100"/&gt;<br>
   * &nbsp;&lt;/filters&gt;<br>
   * &lt;/Console&gt;<br>
   * </code><br>
   */
  
  @Plugin(name = "BurstFilter", category = Node.CATEGORY, elementType = Filter.ELEMENT_TYPE, printObject = true)
  public final class BurstFilter extends AbstractFilter {
  
      private static final long NANOS_IN_SECONDS = 1000000000;
  
      private static final int DEFAULT_RATE = 10;
  
      private static final int DEFAULT_RATE_MULTIPLE = 100;
  
      private static final int HASH_SHIFT = 32;
  
      /**
       * Level of messages to be filtered. Anything at or below this level will be
       * filtered out if <code>maxBurst</code> has been exceeded. The default is
       * WARN meaning any messages that are higher than warn will be logged
       * regardless of the size of a burst.
       */
      private final Level level;
  
      private final long burstInterval;
  
      private final DelayQueue<LogDelay> history = new DelayQueue<>();
  
      private final Queue<LogDelay> available = new ConcurrentLinkedQueue<>();
  
      static LogDelay createLogDelay(final long expireTime) {
          return new LogDelay(expireTime);
      }
      
      private BurstFilter(final Level level, final float rate, final long maxBurst, final Result onMatch,
                          final Result onMismatch) {
          super(onMatch, onMismatch);
          this.level = level;
          this.burstInterval = (long) (NANOS_IN_SECONDS * (maxBurst / rate));
          for (int i = 0; i < maxBurst; ++i) {
              available.add(createLogDelay(0));
          }
      }
  
      @Override
      public Result filter(final Logger logger, final Level level, final Marker marker, final String msg,
                           final Object... params) {
          return filter(level);
      }
 
     @Override
     public Result filter(final Logger logger, final Level level, final Marker marker, final Object msg,
                          final Throwable t) {
         return filter(level);
     }
 
     @Override
     public Result filter(final Logger logger, final Level level, final Marker marker, final Message msg,
                          final Throwable t) {
         return filter(level);
     }
 
     @Override
     public Result filter(final LogEvent event) {
         return filter(event.getLevel());
     }
 
     /**
      * Decide if we're going to log <code>event</code> based on whether the
      * maximum burst of log statements has been exceeded.
      *
      * @param level The log level.
      * @return The onMatch value if the filter passes, onMismatch otherwise.
      */
     private Result filter(final Level level) {
         if (this.level.isMoreSpecificThan(level)) {
             LogDelay delay = history.poll();
             while (delay != null) {
                 available.add(delay);
                 delay = history.poll();
             }
             delay = available.poll();
             if (delay != null) {
                 delay.setDelay(burstInterval);
                 history.add(delay);
                 return onMatch;
             }
             return onMismatch;
         }
         return onMatch;
 
     }
 
     /**
      * Returns the number of available slots. Used for unit testing.
      * @return The number of available slots.
      */
     public int getAvailable() {
         return available.size();
     }
 
     /**
      * Clear the history. Used for unit testing.
      */
     public void clear() {
         for (final LogDelay delay : history) {
             history.remove(delay);
             available.add(delay);
         }
     }
 
     @Override
     public String toString() {
         return "level=" + level.toString() + ", interval=" + burstInterval + ", max=" + history.size();
     }
 
     /**
      * Delay object to represent each log event that has occurred within the timespan.
      * 
      * Consider this class private, package visibility for testing.
      */
     private static class LogDelay implements Delayed {
 
         LogDelay(final long expireTime) {
             this.expireTime = expireTime;
         }
 
         private long expireTime;
 
         public void setDelay(final long delay) {
             this.expireTime = delay + System.nanoTime();
         }
 
         @Override
         public long getDelay(final TimeUnit timeUnit) {
             return timeUnit.convert(expireTime - System.nanoTime(), TimeUnit.NANOSECONDS);
         }
 
         @Override
         public int compareTo(final Delayed delayed) {
             final long diff = this.expireTime - ((LogDelay) delayed).expireTime;
             return Long.signum(diff);
         }
 
         @Override
         public boolean equals(final Object o) {
             if (this == o) {
                 return true;
             }
             if (o == null || getClass() != o.getClass()) {
                 return false;
             }
 
             final LogDelay logDelay = (LogDelay) o;
 
             if (expireTime != logDelay.expireTime) {
                 return false;
             }
 
             return true;
         }
 
         @Override
         public int hashCode() {
             return (int) (expireTime ^ (expireTime >>> HASH_SHIFT));
         }
     }
 
     @PluginBuilderFactory
     public static Builder newBuilder() {
         return new Builder();
     }
 
     public static class Builder implements org.apache.logging.log4j.core.util.Builder<BurstFilter> {
 
         @PluginBuilderAttribute
         private Level level = Level.WARN;
 
         @PluginBuilderAttribute
         private float rate = DEFAULT_RATE;
 
         @PluginBuilderAttribute
         private long maxBurst;
 
         @PluginBuilderAttribute
         private Result onMatch = Result.NEUTRAL;
 
         @PluginBuilderAttribute
         private Result onMismatch = Result.DENY;
 
         /**
          * Sets the logging level to use.
          */
         public Builder setLevel(final Level level) {
             this.level = level;
             return this;
         }
 
         /**
          * Sets the average number of events per second to allow. This must be a positive number.
          */
         public Builder setRate(final float rate) {
             this.rate = rate;
             return this;
         }
 
         /**
          * Sets the maximum number of events that can occur before events are filtered for exceeding the average rate.
          * The default is 10 times the rate.
          */
         public Builder setMaxBurst(final long maxBurst) {
             this.maxBurst = maxBurst;
             return this;
         }
 
         /**
          * Sets the Result to return when the filter matches. Defaults to Result.NEUTRAL.
          */
         public Builder setOnMatch(final Result onMatch) {
             this.onMatch = onMatch;
             return this;
         }
 
         /**
          * Sets the Result to return when the filter does not match. The default is Result.DENY.
          */
         public Builder setOnMismatch(final Result onMismatch) {
             this.onMismatch = onMismatch;
             return this;
         }
 
         @Override
         public BurstFilter build() {
             if (this.rate <= 0) {
                 this.rate = DEFAULT_RATE;
             }
             if (this.maxBurst <= 0) {
                 this.maxBurst = (long) (this.rate * DEFAULT_RATE_MULTIPLE);
             }
             return new BurstFilter(this.level, this.rate, this.maxBurst, this.onMatch, this.onMismatch);
         }
     }
 }