package org.apache.commons.jcs3.log;
   
   /*
    * 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.
   */
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  import java.util.ServiceConfigurationError;
  import java.util.ServiceLoader;
  
  /**
   * This is a borrowed and stripped-down version of the log4j2 LogManager class.
   *
   * The anchor point for the JCS logging system. The most common usage of this
   * class is to obtain a named {@link Log}.
   */
  public class LogManager
  {
      /**
       * The name of log subsystem
       */
      private static String logSystem;
  
      /** Log systems currently known */
      public static final String LOGSYSTEM_JAVA_UTIL_LOGGING = "jul";
      public static final String LOGSYSTEM_LOG4J2 = "log4j2";
  
      /**
       * The SPI LogFactory
       */
      private static class LogFactoryHolder
      {
          static final LogFactory INSTANCE = createLogFactory();
  
          /**
           * Scans the classpath to find a logging implementation.
           *
           * @return the LogFactory
           * @throws RuntimeException, if no factory implementation could be found
           */
          private static LogFactory createLogFactory()
          {
              final ServiceLoader<LogFactory> factories = ServiceLoader.load(LogFactory.class);
              if (LogManager.logSystem == null)
              {
                  LogManager.logSystem = System.getProperty("jcs.logSystem",
                          LOGSYSTEM_JAVA_UTIL_LOGGING);
              }
  
              // Store errors that may occur until log system is available
              List<ServiceConfigurationError> errors = new ArrayList<>();
              Iterator<LogFactory> itr = factories.iterator();
              LogFactory factory = null;
              while (itr.hasNext())
              {
                  try
                  {
                      LogFactory instance = itr.next();
                      if (logSystem.equalsIgnoreCase(instance.getName()))
                      {
                          factory = instance;
                          break;
                      }
                  }
                  catch (ServiceConfigurationError e)
                  {
                      errors.add(e);
                  }
              }
              if (factory != null)
              {
                  if (!errors.isEmpty())
                  {
                      Log log = factory.getLog(LogFactoryHolder.class);
  
                      for (ServiceConfigurationError error : errors)
                      {
                          log.debug("Error loading LogFactory", error);
                      }
                      log.debug("Found LogFactory for " + logSystem);
                  }
                  return factory;
              }
  
             // No log system could be found --> report errors to stderr
             errors.forEach(e -> System.err.println(e.getMessage()));
             throw new RuntimeException("Could not find factory implementation for log subsystem " + logSystem);
         }
     }
 
     /**
      * Set the log system. Must be called before getLog is called
      *
      * @param logSystem the logSystem to set
      */
     public static void setLogSystem(final String logSystem)
     {
         LogManager.logSystem = logSystem;
     }
 
     /**
      * Return the LogFactory
      */
     private static LogFactory getLogFactory()
     {
         return LogFactoryHolder.INSTANCE;
     }
 
     /**
      * Prevents instantiation
      */
     protected LogManager()
     {
     }
 
     /**
      * Shutdown the logging system if the logging system supports it.
      */
     public static void shutdown()
     {
         getLogFactory().shutdown();
     }
 
     /**
      * Returns a Log using the fully qualified name of the Class as the Log
      * name.
      *
      * @param clazz
      *            The Class whose name should be used as the Log name.
      * @return The Log.
      * @throws UnsupportedOperationException
      *             if {@code clazz} is {@code null}
      */
     public static Log getLog(final Class<?> clazz)
     {
         return getLogFactory().getLog(clazz);
     }
 
     /**
      * Returns a Log with the specified name.
      *
      * @param name
      *            The logger name.
      * @return The Log.
      * @throws UnsupportedOperationException
      *             if {@code name} is {@code null}
      */
     public static Log getLog(final String name)
     {
         return getLogFactory().getLog(name);
     }
 
     /**
      * Returns the root logger.
      *
      * @return the root logger, named {@link LogFactory#ROOT_LOGGER_NAME}.
      */
     public static Log getRootLogger()
     {
         return getLog(LogFactory.ROOT_LOGGER_NAME);
     }
 }