/*
    * 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.net.URI;
  import java.util.Objects;
  
  import org.apache.logging.log4j.core.LifeCycle;
  import org.apache.logging.log4j.core.LoggerContext;
  import org.apache.logging.log4j.core.config.Configuration;
  import org.apache.logging.log4j.core.config.ConfigurationFactory;
  import org.apache.logging.log4j.core.config.ConfigurationSource;
  import org.apache.logging.log4j.core.selector.ClassLoaderContextSelector;
  import org.apache.logging.log4j.core.selector.ContextSelector;
  import org.apache.logging.log4j.core.util.Cancellable;
  import org.apache.logging.log4j.core.util.Constants;
  import org.apache.logging.log4j.core.util.DefaultShutdownCallbackRegistry;
  import org.apache.logging.log4j.core.util.Loader;
  import org.apache.logging.log4j.core.util.ShutdownCallbackRegistry;
  import org.apache.logging.log4j.spi.LoggerContextFactory;
  import org.apache.logging.log4j.status.StatusLogger;
  import org.apache.logging.log4j.util.PropertiesUtil;
  
  /**
   * Factory to locate a ContextSelector and then load a LoggerContext.
   */
  public class Log4jContextFactory implements LoggerContextFactory, ShutdownCallbackRegistry {
  
      private static final StatusLogger LOGGER = StatusLogger.getLogger();
      private static final boolean SHUTDOWN_HOOK_ENABLED =
          PropertiesUtil.getProperties().getBooleanProperty(ShutdownCallbackRegistry.SHUTDOWN_HOOK_ENABLED, true);
  
      private final ContextSelector selector;
      private final ShutdownCallbackRegistry shutdownCallbackRegistry;
  
      /**
       * Initializes the ContextSelector from system property {@link Constants#LOG4J_CONTEXT_SELECTOR}.
       */
      public Log4jContextFactory() {
          this(createContextSelector(), createShutdownCallbackRegistry());
      }
  
      /**
       * Initializes this factory's ContextSelector with the specified selector.
       * @param selector the selector to use
       */
      public Log4jContextFactory(final ContextSelector selector) {
          this(selector, createShutdownCallbackRegistry());
      }
  
      /**
       * Constructs a Log4jContextFactory using the ContextSelector from {@link Constants#LOG4J_CONTEXT_SELECTOR}
       * and the provided ShutdownRegistrationStrategy.
       *
       * @param shutdownCallbackRegistry the ShutdownRegistrationStrategy to use
       * @since 2.1
       */
      public Log4jContextFactory(final ShutdownCallbackRegistry shutdownCallbackRegistry) {
          this(createContextSelector(), shutdownCallbackRegistry);
      }
  
      /**
       * Constructs a Log4jContextFactory using the provided ContextSelector and ShutdownRegistrationStrategy.
       *
       * @param selector                     the selector to use
       * @param shutdownCallbackRegistry the ShutdownRegistrationStrategy to use
       * @since 2.1
       */
      public Log4jContextFactory(final ContextSelector selector,
                                 final ShutdownCallbackRegistry shutdownCallbackRegistry) {
          this.selector = Objects.requireNonNull(selector, "No ContextSelector provided");
          this.shutdownCallbackRegistry = Objects.requireNonNull(shutdownCallbackRegistry, "No ShutdownCallbackRegistry provided");
          LOGGER.debug("Using ShutdownCallbackRegistry {}", shutdownCallbackRegistry.getClass());
          initializeShutdownCallbackRegistry();
      }
  
      private static ContextSelector createContextSelector() {
          final String sel = PropertiesUtil.getProperties().getStringProperty(Constants.LOG4J_CONTEXT_SELECTOR);
          if (sel != null) {
              try {
                  return Loader.newCheckedInstanceOf(sel, ContextSelector.class);
              } catch (final Exception ex) {
                  LOGGER.error("Unable to create context {}", sel, ex);
              }
          }
         return new ClassLoaderContextSelector();
     }
 
     private static ShutdownCallbackRegistry createShutdownCallbackRegistry() {
         // TODO: this is such a common idiom it really deserves a utility method somewhere
         final String registry = PropertiesUtil.getProperties().getStringProperty(
             ShutdownCallbackRegistry.SHUTDOWN_CALLBACK_REGISTRY);
         if (registry != null) {
             try {
                 return Loader.newCheckedInstanceOf(registry, ShutdownCallbackRegistry.class);
             } catch (final Exception e) {
                 LOGGER.error(SHUTDOWN_HOOK_MARKER,
                     "There was an error loading the ShutdownCallbackRegistry [{}]. "
                         + "Falling back to DefaultShutdownCallbackRegistry.", registry, e);
             }
         }
         return new DefaultShutdownCallbackRegistry();
     }
 
     private void initializeShutdownCallbackRegistry() {
         if (SHUTDOWN_HOOK_ENABLED && this.shutdownCallbackRegistry instanceof LifeCycle) {
             try {
                 ((LifeCycle) this.shutdownCallbackRegistry).start();
             } catch (final Exception e) {
                 LOGGER.error("There was an error starting the ShutdownCallbackRegistry.", e);
             }
         }
     }
 
     /**
      * Loads the LoggerContext using the ContextSelector.
      * @param fqcn The fully qualified class name of the caller.
      * @param loader The ClassLoader to use or null.
      * @param currentContext If true returns the current Context, if false returns the Context appropriate
      * for the caller if a more appropriate Context can be determined.
      * @param externalContext An external context (such as a ServletContext) to be associated with the LoggerContext.
      * @return The LoggerContext.
      */
     @Override
     public LoggerContext getContext(final String fqcn, final ClassLoader loader, final Object externalContext,
                                     final boolean currentContext) {
         final LoggerContext ctx = selector.getContext(fqcn, loader, currentContext);
         if (externalContext != null && ctx.getExternalContext() == null) {
             ctx.setExternalContext(externalContext);
         }
         if (ctx.getState() == LifeCycle.State.INITIALIZED) {
             ctx.start();
         }
         return ctx;
     }
 
     /**
      * Loads the LoggerContext using the ContextSelector.
      * @param fqcn The fully qualified class name of the caller.
      * @param loader The ClassLoader to use or null.
      * @param externalContext An external context (such as a ServletContext) to be associated with the LoggerContext.
      * @param currentContext If true returns the current Context, if false returns the Context appropriate
      * for the caller if a more appropriate Context can be determined.
      * @param source The configuration source.
      * @return The LoggerContext.
      */
     public LoggerContext getContext(final String fqcn, final ClassLoader loader, final Object externalContext,
                                     final boolean currentContext, final ConfigurationSource source) {
         final LoggerContext ctx = selector.getContext(fqcn, loader, currentContext, null);
         if (externalContext != null && ctx.getExternalContext() == null) {
             ctx.setExternalContext(externalContext);
         }
         if (ctx.getState() == LifeCycle.State.INITIALIZED) {
             if (source != null) {
                 ContextAnchor.THREAD_CONTEXT.set(ctx);
                 final Configuration config = ConfigurationFactory.getInstance().getConfiguration(source);
                 LOGGER.debug("Starting LoggerContext[name={}] from configuration {}", ctx.getName(), source);
                 ctx.start(config);
                 ContextAnchor.THREAD_CONTEXT.remove();
             } else {
                 ctx.start();
             }
         }
         return ctx;
     }
 
     /**
      * Loads the LoggerContext using the ContextSelector using the provided Configuration
      * @param fqcn The fully qualified class name of the caller.
      * @param loader The ClassLoader to use or null.
      * @param externalContext An external context (such as a ServletContext) to be associated with the LoggerContext.
      * @param currentContext If true returns the current Context, if false returns the Context appropriate
      * for the caller if a more appropriate Context can be determined.
      * @param configuration The Configuration.
      * @return The LoggerContext.
      */
     public LoggerContext getContext(final String fqcn, final ClassLoader loader, final Object externalContext,
             final boolean currentContext, final Configuration configuration) {
         final LoggerContext ctx = selector.getContext(fqcn, loader, currentContext, null);
         if (externalContext != null && ctx.getExternalContext() == null) {
             ctx.setExternalContext(externalContext);
         }
         if (ctx.getState() == LifeCycle.State.INITIALIZED) {
             ContextAnchor.THREAD_CONTEXT.set(ctx);
             try {
                 ctx.start(configuration);
             } finally {
                 ContextAnchor.THREAD_CONTEXT.remove();
             }
         }
         return ctx;
     }
 
     /**
      * Loads the LoggerContext using the ContextSelector.
      * @param fqcn The fully qualified class name of the caller.
      * @param loader The ClassLoader to use or null.
      * @param externalContext An external context (such as a ServletContext) to be associated with the LoggerContext.
      * @param currentContext If true returns the current Context, if false returns the Context appropriate
      * for the caller if a more appropriate Context can be determined.
      * @param configLocation The location of the configuration for the LoggerContext (or null).
      * @return The LoggerContext.
      */
     @Override
     public LoggerContext getContext(final String fqcn, final ClassLoader loader, final Object externalContext,
                                     final boolean currentContext, final URI configLocation, final String name) {
         final LoggerContext ctx = selector.getContext(fqcn, loader, currentContext, configLocation);
         if (externalContext != null && ctx.getExternalContext() == null) {
             ctx.setExternalContext(externalContext);
         }
         if (ctx.getState() == LifeCycle.State.INITIALIZED) {
             if (configLocation != null || name != null) {
                 ContextAnchor.THREAD_CONTEXT.set(ctx);
                 final Configuration config = ConfigurationFactory.getInstance().getConfiguration(name, configLocation);
                 LOGGER.debug("Starting LoggerContext[name={}] from configuration at {}", ctx.getName(), configLocation);
                 ctx.start(config);
                 ContextAnchor.THREAD_CONTEXT.remove();
             } else {
                 ctx.start();
             }
         }
         return ctx;
     }
 
     /**
      * Returns the ContextSelector.
      * @return The ContextSelector.
      */
     public ContextSelector getSelector() {
         return selector;
     }
 
 	/**
 	 * Returns the ShutdownCallbackRegistry
 	 * 
 	 * @return the ShutdownCallbackRegistry
 	 * @since 2.4
 	 */
 	public ShutdownCallbackRegistry getShutdownCallbackRegistry() {
 		return shutdownCallbackRegistry;
 	}
 
     /**
      * Removes knowledge of a LoggerContext.
      *
      * @param context The context to remove.
      */
     @Override
     public void removeContext(final org.apache.logging.log4j.spi.LoggerContext context) {
         if (context instanceof LoggerContext) {
             selector.removeContext((LoggerContext) context);
         }
     }
 
     @Override
     public Cancellable addShutdownCallback(final Runnable callback) {
         return SHUTDOWN_HOOK_ENABLED ? shutdownCallbackRegistry.addShutdownCallback(callback) : null;
     }
 
 }