package org.apache.maven;
   
   /*
    * 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 java.util.LinkedList;
  import java.util.Map;
  
  import com.google.common.collect.Maps;
  import com.google.inject.Key;
  import com.google.inject.OutOfScopeException;
  import com.google.inject.Provider;
  import com.google.inject.Scope;
  import com.google.inject.util.Providers;
  
  public class SessionScope
      implements Scope
  {    
      private static final Provider<Object> SEEDED_KEY_PROVIDER = new Provider<Object>()
      {
          public Object get()
          {
              throw new IllegalStateException();
          }
      };
  
      private static final class ScopeState
      {
          public final Map<Key<?>, Provider<?>> seeded = Maps.newHashMap();
  
          public final Map<Key<?>, Object> provided = Maps.newHashMap();
      }
  
      private final ThreadLocal<LinkedList<ScopeState>> values = new ThreadLocal<LinkedList<ScopeState>>();
  
      public void enter()
      {
          LinkedList<ScopeState> stack = values.get();
          if ( stack == null )
          {
              stack = new LinkedList<ScopeState>();
              values.set( stack );
          }
          stack.addFirst( new ScopeState() );
      }
  
      private ScopeState getScopeState()
      {
          LinkedList<ScopeState> stack = values.get();
          if ( stack == null || stack.isEmpty() )
          {
              throw new IllegalStateException();
          }
          return stack.getFirst();
      }
  
      public void exit()
      {
          final LinkedList<ScopeState> stack = values.get();
          if ( stack == null || stack.isEmpty() )
          {
              throw new IllegalStateException();
          }
          stack.removeFirst();
          if ( stack.isEmpty() )
          {
              values.remove();
          }
      }
  
      public <T> void seed( Class<T> clazz, Provider<T> value )
      {
          getScopeState().seeded.put( Key.get( clazz ), value );
      }
  
      public <T> void seed( Class<T> clazz, final T value )
      {
          getScopeState().seeded.put( Key.get( clazz ), Providers.of( value ) );
      }
  
      public <T> Provider<T> scope( final Key<T> key, final Provider<T> unscoped )
      {
          return new Provider<T>()
         {
             @SuppressWarnings( "unchecked" )
             public T get()
             {
                 LinkedList<ScopeState> stack = values.get();
                 if ( stack == null || stack.isEmpty() )
                 {
                     throw new OutOfScopeException( "Cannot access " + key + " outside of a scoping block" );
                 }
 
                 ScopeState state = stack.getFirst();
 
                 Provider<?> seeded = state.seeded.get( key );
 
                 if ( seeded != null )
                 {
                     return (T) seeded.get();
                 }
 
                 T provided = (T) state.provided.get( key );
                 if ( provided == null && unscoped != null )
                 {
                     provided = unscoped.get();
                     state.provided.put( key, provided );
                 }
 
                 return provided;
             }
         };
     }
 
     @SuppressWarnings( { "unchecked" } )
     public static <T> Provider<T> seededKeyProvider()
     {
         return (Provider<T>) SEEDED_KEY_PROVIDER;
     }
 }