/*
    * 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.layout;
  
  import org.apache.logging.log4j.core.LogEvent;
  import org.apache.logging.log4j.core.config.plugins.Plugin;
  import org.apache.logging.log4j.core.config.plugins.PluginAttr;
  import org.apache.logging.log4j.core.config.plugins.PluginFactory;
  import org.apache.logging.log4j.core.net.Facility;
  import org.apache.logging.log4j.core.net.Priority;
  import org.apache.logging.log4j.util.EnglishEnums;
  
  import java.net.InetAddress;
  import java.net.UnknownHostException;
  import java.nio.charset.Charset;
  import java.text.SimpleDateFormat;
  import java.util.Date;
  import java.util.Locale;
  
  
  /**
   * Formats a log event as a BSD Log record.
   */
  @Plugin(name = "SyslogLayout", type = "Core", elementType = "layout", printObject = true)
  public class SyslogLayout extends AbstractStringLayout {
  
      private final Facility facility;
      private final boolean includeNewLine;
  
      /**
       * Date format used if header = true.
       */
      private final SimpleDateFormat dateFormat = new SimpleDateFormat("MMM dd HH:mm:ss ", Locale.ENGLISH);
      /**
       * Host name used to identify messages from this appender.
       */
      private final String localHostname = getLocalHostname();
  
  
      protected SyslogLayout(Facility facility, boolean includeNL, Charset c) {
          super(c);
          this.facility = facility;
          this.includeNewLine = includeNL;
      }
  
      /**
       * Formats a {@link org.apache.logging.log4j.core.LogEvent} in conformance with the log4j.dtd.
       *
       * @param event The LogEvent
       * @return the event formatted as a String.
       */
      public String toSerializable(final LogEvent event) {
          StringBuilder buf = new StringBuilder();
  
          buf.append("<");
          buf.append(Priority.getPriority(facility, event.getLevel()));
          buf.append(">");
          addDate(event.getMillis(), buf);
          buf.append(" ");
          buf.append(localHostname);
          buf.append(" ");
          buf.append(event.getMessage().getFormattedMessage());
          if (includeNewLine) {
              buf.append("\n");
          }
          return buf.toString();
      }
  
      /**
       * This method gets the network name of the machine we are running on.
       * Returns "UNKNOWN_LOCALHOST" in the unlikely case where the host name
       * cannot be found.
       *
       * @return String the name of the local host
       */
      private String getLocalHostname() {
          try {
              InetAddress addr = InetAddress.getLocalHost();
              return addr.getHostName();
          } catch (UnknownHostException uhe) {
              LOGGER.error("Could not determine local host name", uhe);
              return "UNKNOWN_LOCALHOST";
          }
      }
  
     private synchronized void addDate(final long timestamp, StringBuilder buf) {
         int index = buf.length() + 4;
         buf.append(dateFormat.format(new Date(timestamp)));
         //  RFC 3164 says leading space, not leading zero on days 1-9
         if (buf.charAt(index) == '0') {
             buf.setCharAt(index, ' ');
         }
     }
 
     /**
      * Create a SyslogLayout.
      * @param facility The Facility is used to try to classify the message.
      * @param includeNL If true a newline will be appended to the result.
      * @param charset The character set.
      * @return A SyslogLayout.
      */
     @PluginFactory
     public static SyslogLayout createLayout(@PluginAttr("facility") String facility,
                                             @PluginAttr("newLine") String includeNL,
                                             @PluginAttr("charset") String charset) {
 
         Charset c = Charset.isSupported("UTF-8") ? Charset.forName("UTF-8") : Charset.defaultCharset();
         if (charset != null) {
             if (Charset.isSupported(charset)) {
                 c = Charset.forName(charset);
             } else {
                 LOGGER.error("Charset " + charset + " is not supported for layout, using " + c.displayName());
             }
         }
         boolean includeNewLine = includeNL == null ? false : Boolean.valueOf(includeNL);
         Facility f = Facility.toFacility(facility, Facility.LOCAL0);
         return new SyslogLayout(f, includeNewLine, c);
     }
 }