package org.slf4j.helpers;
   
   import java.util.ArrayDeque;
   import java.util.Deque;
   import java.util.HashMap;
   import java.util.Map;
   
   
   /**
   * A simple implementation of ThreadLocal backed Map containing values of type 
   * Deque<String>.
   * 
   * @author Ceki Guuml;c&uuml;
   * @since 2.0.0
   */
  public class ThreadLocalMapOfStacks {
  
      final ThreadLocal<Map<String, Deque<String>>> tlMapOfStacks = new ThreadLocal<>();
  
      public void pushByKey(String key, String value) {
          if (key == null)
              return;
  
          Map<String, Deque<String>> map = tlMapOfStacks.get();
  
          if (map == null) {
              map = new HashMap<>();
              tlMapOfStacks.set(map);
          }
  
          Deque<String> deque = map.get(key);
          if (deque == null) {
              deque = new ArrayDeque<>();
          }
          deque.push(value);
          map.put(key, deque);
      }
  
      public String popByKey(String key) {
          if (key == null)
              return null;
  
          Map<String, Deque<String>> map = tlMapOfStacks.get();
          if (map == null)
              return null;
          Deque<String> deque = map.get(key);
          if (deque == null)
              return null;
          return deque.pop();
      }
  
      public Deque<String> getCopyOfDequeByKey(String key) {
          if (key == null)
              return null;
  
          Map<String, Deque<String>> map = tlMapOfStacks.get();
          if (map == null)
              return null;
          Deque<String> deque = map.get(key);
          if (deque == null)
              return null;
  
          return new ArrayDeque<String>(deque);
      }
      
      /**
       * Clear the deque(stack) referenced by 'key'. 
       * 
       * @param key identifies the  stack
       * 
       * @since 2.0.0
       */
      public void clearDequeByKey(String key) {
          if (key == null)
              return;
  
          Map<String, Deque<String>> map = tlMapOfStacks.get();
          if (map == null)
              return;
          Deque<String> deque = map.get(key);
          if (deque == null)
              return;
          deque.clear();
      }
  
  }