/*
    * 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.slf4j.helpers;
  
  import java.util.Map;
  import java.util.WeakHashMap;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.spi.AbstractLogger;
  import org.apache.logging.log4j.spi.LoggerContext;
  import org.apache.logging.slf4j.SLF4JLoggingException;
  import org.slf4j.ILoggerFactory;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.slf4j.impl.SLF4JLogger;
  
  /**
   *
   */
  public class Log4jLoggerFactory implements ILoggerFactory {
  
      private static final String FQCN = Log4jLoggerFactory.class.getName();
      private static final String PACKAGE = "org.slf4j";
  
      private final Map<LoggerContext, ConcurrentMap<String, Logger>> contextMap =
          new WeakHashMap<LoggerContext, ConcurrentMap<String, Logger>>();
  
      @Override
      public Logger getLogger(final String name) {
          final LoggerContext context = getContext();
          final ConcurrentMap<String, Logger> loggers = getLoggersMap(context);
  
          if (loggers.containsKey(name)) {
              return loggers.get(name);
          }
          final String key = Logger.ROOT_LOGGER_NAME.equals(name) ? LogManager.ROOT_LOGGER_NAME : name;
          final org.apache.logging.log4j.Logger logger = context.getLogger(key);
          if (logger instanceof AbstractLogger) {
              loggers.putIfAbsent(name, new SLF4JLogger((AbstractLogger) logger, name));
              return loggers.get(name);
          }
          throw new SLF4JLoggingException("SLF4J Adapter requires base logging system to extend Log4j AbstractLogger");
      }
  
      private ConcurrentMap<String, Logger> getLoggersMap(final LoggerContext context) {
          synchronized (contextMap) {
              ConcurrentMap<String, Logger> map = contextMap.get(context);
              if (map == null) {
                  map = new ConcurrentHashMap<String, Logger>();
                  contextMap.put(context, map);
              }
              return map;
          }
      }
      private LoggerContext getContext() {
          final Throwable t = new Throwable();
          boolean next = false;
          boolean pkg = false;
          String fqcn = LoggerFactory.class.getName();
          for (final StackTraceElement element : t.getStackTrace()) {
              if (FQCN.equals(element.getClassName())) {
                  next = true;
                  continue;
              }
              if (next && element.getClassName().startsWith(PACKAGE)) {
                  fqcn = element.getClassName();
                  pkg = true;
                  continue;
              }
              if (pkg) {
                  break;
              }
          }
          return PrivateManager.getContext(fqcn);
      }
  
      /**
       * The real bridge between SLF4J and Log4j.
       */
      private static class PrivateManager extends LogManager {
          private static final String FQCN = LoggerFactory.class.getName();
  
          public static LoggerContext getContext() {
             return getContext(FQCN, false);
         }
 
         public static LoggerContext getContext(final String fqcn) {
             return getContext(fqcn, false);
         }
 
         public static org.apache.logging.log4j.Logger getLogger(final String name) {
             return getLogger(FQCN, name);
         }
     }
 
 }