/*
    * 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.jul;
  
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.HashSet;
  import java.util.Set;
  import java.util.logging.Logger;
  
  import org.apache.logging.log4j.LoggingException;
  import org.apache.logging.log4j.status.StatusLogger;
  import org.apache.logging.log4j.util.LoaderUtil;
  import org.apache.logging.log4j.util.PropertiesUtil;
  
  /**
   * Log4j implementation of {@link java.util.logging.LogManager}. Note that the system property
   * {@code java.util.logging.manager} must be set to {@code org.apache.logging.log4j.jul.LogManager} in order to use
   * this adaptor. This LogManager requires the {@code log4j-api} library to be available. If {@code log4j-core} is
   * also available, then more features of {@link java.util.logging.Logger} are supported.
   *
   * <p>To override the default {@link AbstractLoggerAdapter} that is used, specify the Log4j property
   * {@code log4j.jul.LoggerAdapter} and set it to the fully qualified class name of a custom
   * implementation. All implementations must have a default constructor.</p>
   *
   * @since 2.1
   */
  public class LogManager extends java.util.logging.LogManager {
  
      private static final org.apache.logging.log4j.Logger LOGGER = StatusLogger.getLogger();
      private final AbstractLoggerAdapter loggerAdapter;
      // Contains the set of logger names that are actively being requested using getLogger.
      private final ThreadLocal<Set<String>> recursive = ThreadLocal.withInitial(HashSet::new);
  
      public LogManager() {
          super();
          AbstractLoggerAdapter adapter = null;
          final String overrideAdaptorClassName =
              PropertiesUtil.getProperties().getStringProperty(Constants.LOGGER_ADAPTOR_PROPERTY);
          if (overrideAdaptorClassName != null) {
              try {
                  LOGGER.info("Trying to use LoggerAdaptor [{}] specified by Log4j property.", overrideAdaptorClassName);
                  adapter = LoaderUtil.newCheckedInstanceOf(overrideAdaptorClassName, AbstractLoggerAdapter.class);
              } catch (final Exception e) {
                  LOGGER.error("Specified LoggerAdapter [{}] is incompatible.", overrideAdaptorClassName, e);
              }
          }
          if (adapter == null) {
              // default adapter
              String adapterClassName;
              try {
                  // find out if log4j-core is available
                  LoaderUtil.loadClass(Constants.CORE_LOGGER_CLASS_NAME);
                  adapterClassName = Constants.CORE_LOGGER_ADAPTER_CLASS_NAME;
              } catch (final ClassNotFoundException ignored) {
                  adapterClassName = Constants.API_LOGGER_ADAPTER_CLASS_NAME;
              }
              LOGGER.debug("Attempting to use {}", adapterClassName);
              try {
                  adapter = LoaderUtil.newCheckedInstanceOf(adapterClassName, AbstractLoggerAdapter.class);
              } catch (final Exception e) {
                  throw LOGGER.throwing(new LoggingException(e));
              }
          }
          loggerAdapter = adapter;
          LOGGER.info("Registered Log4j as the java.util.logging.LogManager.");
      }
  
      @Override
      public boolean addLogger(final Logger logger) {
          // in order to prevent non-bridged loggers from being registered, we always return false to indicate that
          // the named logger should be obtained through getLogger(name)
          return false;
      }
  
      @Override
      public Logger getLogger(final String name) {
          LOGGER.trace("Call to LogManager.getLogger({})", name);
          Set<String> activeRequests = recursive.get();
          if (activeRequests.add(name)) {
              try {
                  return loggerAdapter.getLogger(name);
              } finally {
                  activeRequests.remove(name);
              }
         } else {
             LOGGER.warn("Recursive call to getLogger for {} ignored.", name);
             return new NoOpLogger(name);
         }
     }
 
     @Override
     public Enumeration<String> getLoggerNames() {
         return Collections.enumeration(loggerAdapter.getLoggersInContext(loggerAdapter.getContext()).keySet());
     }
 
 }