/*
    * 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.impl;
  
  import java.util.List;
  
  import org.apache.logging.log4j.Level;
  import org.apache.logging.log4j.Marker;
  import org.apache.logging.log4j.ThreadContext;
  import org.apache.logging.log4j.core.ContextDataInjector;
  import org.apache.logging.log4j.core.LogEvent;
  import org.apache.logging.log4j.core.async.ThreadNameCachingStrategy;
  import org.apache.logging.log4j.core.config.Property;
  import org.apache.logging.log4j.core.util.Clock;
  import org.apache.logging.log4j.core.util.ClockFactory;
  import org.apache.logging.log4j.message.Message;
  import org.apache.logging.log4j.util.StringMap;
  
  /**
   * Garbage-free LogEventFactory that reuses a single mutable log event.
   * @since 2.6
   */
  public class ReusableLogEventFactory implements LogEventFactory, LocationAwareLogEventFactory {
      private static final ThreadNameCachingStrategy THREAD_NAME_CACHING_STRATEGY = ThreadNameCachingStrategy.create();
      private static final Clock CLOCK = ClockFactory.getClock();
  
      private static ThreadLocal<MutableLogEvent> mutableLogEventThreadLocal = new ThreadLocal<>();
      private final ContextDataInjector injector = ContextDataInjectorFactory.createInjector();
  
      /**
       * Creates a log event.
       *
       * @param loggerName The name of the Logger.
       * @param marker An optional Marker.
       * @param fqcn The fully qualified class name of the caller.
       * @param level The event Level.
       * @param message The Message.
       * @param properties Properties to be added to the log event.
       * @param t An optional Throwable.
       * @return The LogEvent.
       */
      @Override
      public LogEvent createEvent(final String loggerName, final Marker marker,
          final String fqcn, final Level level, final Message message,
          final List<Property> properties, final Throwable t) {
          return createEvent(loggerName, marker, fqcn, null, level, message, properties, t);
      }
  
      /**
       * Creates a log event.
       *
       * @param loggerName The name of the Logger.
       * @param marker An optional Marker.
       * @param fqcn The fully qualified class name of the caller.
       * @param location The location of the caller.
       * @param level The event Level.
       * @param message The Message.
       * @param properties Properties to be added to the log event.
       * @param t An optional Throwable.
       * @return The LogEvent.
       */
      @Override
      public LogEvent createEvent(final String loggerName, final Marker marker, final String fqcn,
                                  final StackTraceElement location, final Level level, final Message message,
                                  final List<Property> properties, final Throwable t) {
          MutableLogEvent result = mutableLogEventThreadLocal.get();
          if (result == null || result.reserved) {
              final boolean initThreadLocal = result == null;
              result = new MutableLogEvent();
  
              // usually no need to re-initialize thread-specific fields since the event is stored in a ThreadLocal
              result.setThreadId(Thread.currentThread().getId());
              result.setThreadName(Thread.currentThread().getName()); // Thread.getName() allocates Objects on each call
              result.setThreadPriority(Thread.currentThread().getPriority());
              if (initThreadLocal) {
                  mutableLogEventThreadLocal.set(result);
              }
          }
          result.reserved = true;
          result.clear(); // ensure any previously cached values (thrownProxy, source, etc.) are cleared
  
          result.setLoggerName(loggerName);
          result.setMarker(marker);
          result.setLoggerFqcn(fqcn);
          result.setLevel(level == null ? Level.OFF : level);
         result.setMessage(message);
         result.initTime(CLOCK, Log4jLogEvent.getNanoClock());
         result.setThrown(t);
         result.setSource(location);
         result.setContextData(injector.injectContextData(properties, (StringMap) result.getContextData()));
         result.setContextStack(ThreadContext.getDepth() == 0 ? ThreadContext.EMPTY_STACK : ThreadContext.cloneStack());// mutable copy
 
         if (THREAD_NAME_CACHING_STRATEGY == ThreadNameCachingStrategy.UNCACHED) {
             result.setThreadName(Thread.currentThread().getName()); // Thread.getName() allocates Objects on each call
             result.setThreadPriority(Thread.currentThread().getPriority());
         }
         return result;
     }
 
     /**
      * Switches the {@code reserved} flag off if the specified event is a MutableLogEvent, otherwise does nothing.
      * This flag is used internally to verify that a reusable log event is no longer in use and can be reused.
      * @param logEvent the log event to make available again
      * @since 2.7
      */
     public static void release(final LogEvent logEvent) { // LOG4J2-1583
         if (logEvent instanceof MutableLogEvent) {
             final MutableLogEvent mutableLogEvent = (MutableLogEvent) logEvent;
             mutableLogEvent.clear();
             mutableLogEvent.reserved = false;
         }
     }
 }