package org.apache.maven.session.scope.internal;
   
   /*
    * 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.Collections;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.Map;
  
  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;
  
  /**
   * SessionScope
   */
  public class SessionScope
      implements Scope
  {
      /**
       * @since 3.3.0
       */
      public static class Memento
      {
          final Map<Key<?>, Provider<?>> seeded;
  
          Memento( final Map<Key<?>, Provider<?>> seeded )
          {
              this.seeded = Collections.unmodifiableMap( new HashMap<>( seeded ) );
          }
      }
  
      private static final Provider<Object> SEEDED_KEY_PROVIDER = new Provider<Object>()
      {
          public Object get()
          {
              throw new IllegalStateException();
          }
      };
  
      /**
       * ScopeState
       */
      private static final class ScopeState
      {
          private final Map<Key<?>, Provider<?>> seeded = new HashMap<>();
  
          private final Map<Key<?>, Object> provided = new HashMap<>();
      }
  
      private final ThreadLocal<LinkedList<ScopeState>> values = new ThreadLocal<>();
  
      public void enter()
      {
          LinkedList<ScopeState> stack = values.get();
          if ( stack == null )
          {
              stack = new LinkedList<>();
              values.set( stack );
          }
          stack.addFirst( new ScopeState() );
      }
  
      /**
       * @since 3.3.0
       */
      public void enter( Memento memento )
      {
          enter();
          getScopeState().seeded.putAll( memento.seeded );
      }
  
      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();
         }
     }
 
     /**
      * @since 3.3.0
      */
     public Memento memento()
     {
         LinkedList<ScopeState> stack = values.get();
         return new Memento( stack != null ? stack.getFirst().seeded : Collections.<Key<?>, Provider<?>>emptyMap() );
     }
 
     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;
     }
 }