/**
    * Logback: the reliable, generic, fast and flexible logging framework.
    * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
    *
    * This program and the accompanying materials are dual-licensed under
    * either the terms of the Eclipse Public License v1.0 as published by
    * the Eclipse Foundation
    *
    *   or (per the licensee's choosing)
   *
   * under the terms of the GNU Lesser General Public License version 2.1
   * as published by the Free Software Foundation.
   */
  package ch.qos.logback.classic.pattern;
  
  import ch.qos.logback.classic.spi.ILoggingEvent;
  
  import java.util.Map;
  
  import static ch.qos.logback.core.util.OptionHelper.extractDefaultReplacement;
  
  public class MDCConverter extends ClassicConverter {
  
      private String key;
      private String defaultValue = "";
  
      @Override
      public void start() {
          String[] keyInfo = extractDefaultReplacement(getFirstOption());
          key = keyInfo[0];
          if (keyInfo[1] != null) {
              defaultValue = keyInfo[1];
          }
          super.start();
      }
  
      @Override
      public void stop() {
          key = null;
          super.stop();
      }
  
      @Override
      public String convert(ILoggingEvent event) {
          Map<String, String> mdcPropertyMap = event.getMDCPropertyMap();
  
          if (mdcPropertyMap == null) {
              return defaultValue;
          }
  
          if (key == null) {
              return outputMDCForAllKeys(mdcPropertyMap);
          } else {
  
              String value = mdcPropertyMap.get(key);
              if (value != null) {
                  return value;
              } else {
                  return defaultValue;
              }
          }
      }
  
      /**
       * if no key is specified, return all the values present in the MDC, in the
       * format "k1=v1, k2=v2, ..."
       */
      private String outputMDCForAllKeys(Map<String, String> mdcPropertyMap) {
          StringBuilder buf = new StringBuilder();
          boolean first = true;
          for (Map.Entry<String, String> entry : mdcPropertyMap.entrySet()) {
              if (first) {
                  first = false;
              } else {
                  buf.append(", ");
              }
              // format: key0=value0, key1=value1
              buf.append(entry.getKey()).append('=').append(entry.getValue());
          }
          return buf.toString();
      }
  
      /**
       * PrefixCompositeConverter needs the key
       * 
       * @return
       */
      public String getKey() {
          return key;
      }
  
  }