package org.eclipse.aether;
   
   /*
    * 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.
   */
  
  import static java.util.Objects.requireNonNull;
  
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import java.util.function.Supplier;
  
  /**
   * A simple session data storage backed by a thread-safe map.
   */
  public final class DefaultSessionData
      implements SessionData
  {
  
      private final ConcurrentMap<Object, Object> data;
  
      public DefaultSessionData()
      {
          data = new ConcurrentHashMap<>();
      }
  
      public void set( Object key, Object value )
      {
          requireNonNull( key, "key cannot be null" );
  
          if ( value != null )
          {
              data.put( key, value );
          }
          else
          {
              data.remove( key );
          }
      }
  
      public boolean set( Object key, Object oldValue, Object newValue )
      {
          requireNonNull( key, "key cannot be null" );
  
          if ( newValue != null )
          {
              if ( oldValue == null )
              {
                  return data.putIfAbsent( key, newValue ) == null;
              }
              return data.replace( key, oldValue, newValue );
          }
          else
          {
              if ( oldValue == null )
              {
                  return !data.containsKey( key );
              }
              return data.remove( key, oldValue );
          }
      }
  
      public Object get( Object key )
      {
          requireNonNull( key, "key cannot be null" );
  
          return data.get( key );
      }
  
      public Object computeIfAbsent( Object key, Supplier<Object> supplier )
      {
          return data.computeIfAbsent( key, k -> supplier.get() );
      }
  }