/*
    * 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.web.appender;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.core.Filter;
  import org.apache.logging.log4j.core.Layout;
  import org.apache.logging.log4j.core.LogEvent;
  import org.apache.logging.log4j.core.LoggerContext;
  import org.apache.logging.log4j.core.appender.AbstractAppender;
  import org.apache.logging.log4j.core.config.plugins.Plugin;
  import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
  import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
  import org.apache.logging.log4j.core.config.plugins.PluginElement;
  import org.apache.logging.log4j.core.config.plugins.PluginFactory;
  import org.apache.logging.log4j.core.impl.ContextAnchor;
  import org.apache.logging.log4j.core.layout.AbstractStringLayout;
  import org.apache.logging.log4j.core.layout.PatternLayout;
  import org.apache.logging.log4j.core.util.Booleans;
  
  import javax.servlet.ServletContext;
  import java.io.Serializable;
  
  /**
   * Logs using the ServletContext's log method
   */
  @Plugin(name = "Servlet", category = "Core", elementType = "appender", printObject = true)
  public class ServletAppender extends AbstractAppender {
      private final ServletContext servletContext;
  
      private ServletAppender(final String name, final AbstractStringLayout layout, final Filter filter,
                              final ServletContext servletContext, final boolean ignoreExceptions) {
          super(name, filter, layout, ignoreExceptions);
          this.servletContext = servletContext;
      }
  
      @Override
      public void append(final LogEvent event) {
          servletContext.log(((AbstractStringLayout) getLayout()).toSerializable(event));
      }
  
      /**
       * Create a Console Appender.
       * @param layout The layout to use (required).
       * @param filter The Filter or null.
       * @param name The name of the Appender (required).
       * @param ignore If {@code "true"} (default) exceptions encountered when appending events are logged; otherwise
       *               they are propagated to the caller.
       * @return The ServletAppender.
       */
      @PluginFactory
      public static ServletAppender createAppender(
              @PluginElement("Layout") Layout<? extends Serializable> layout,
              @PluginElement("Filter") final Filter filter,
              @PluginAttribute("name") final String name,
              @PluginAttribute(value = "ignoreExceptions", defaultBoolean = true) final String ignore) {
          if (name == null) {
              LOGGER.error("No name provided for ConsoleAppender");
              return null;
          }
          final ServletContext servletContext = getServletContext();
          if (servletContext == null) {
              LOGGER.error("No servlet context is available");
              return null;
          }
          if (layout == null) {
              layout = PatternLayout.createDefaultLayout();
          } else if (!(layout instanceof AbstractStringLayout)) {
              LOGGER.error("Layout must be a StringLayout to log to ServletContext");
              return null;
          }
          final boolean ignoreExceptions = Booleans.parseBoolean(ignore, true);
          return new ServletAppender(name, (AbstractStringLayout) layout, filter, servletContext, ignoreExceptions);
      }
  
      private static ServletContext getServletContext() {
          LoggerContext lc = ContextAnchor.THREAD_CONTEXT.get();
          if (lc == null) {
              lc = (LoggerContext) LogManager.getContext(false);
          }
          if (lc != null) {
              final Object obj = lc.getExternalContext();
              return obj != null && obj instanceof ServletContext ? (ServletContext) obj : null;
          }
          return null;
     }
 }