package org.apache.maven.model.building;
   
   /*
    * 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.nio.file.Path;
  import java.util.Map;
  import java.util.Objects;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.function.Supplier;
  
  import org.apache.maven.model.Model;
  
  /**
   *
   * @author Robert Scholte
   * @since 4.0.0
   */
  class DefaultTransformerContext implements TransformerContext
  {
      final Map<String, String> userProperties = new ConcurrentHashMap<>();
  
      final Map<Path, Holder> modelByPath = new ConcurrentHashMap<>();
  
      final Map<GAKey, Holder> modelByGA = new ConcurrentHashMap<>();
  
      public static class Holder
      {
          private volatile boolean set;
          private volatile Model model;
  
          Holder()
          {
          }
  
          public static Model deref( Holder holder )
          {
              return holder != null ? holder.get() : null;
          }
  
          public Model get()
          {
              if ( !set )
              {
                  synchronized ( this )
                  {
                      if ( !set )
                      {
                          try
                          {
                              this.wait();
                          }
                          catch ( InterruptedException e )
                          {
                              // Ignore
                          }
                      }
                  }
              }
              return model;
          }
  
          public Model computeIfAbsent( Supplier<Model> supplier )
          {
              if ( !set )
              {
                  synchronized ( this )
                  {
                      if ( !set )
                      {
                          this.set = true;
                          this.model = supplier.get();
                          this.notifyAll();
                      }
                  }
              }
              return model;
          }
  
      }
  
      @Override
      public String getUserProperty( String key )
     {
         return userProperties.get( key );
     }
 
     @Override
     public Model getRawModel( Path p )
     {
         return Holder.deref( modelByPath.get( p ) );
     }
 
     @Override
     public Model getRawModel( String groupId, String artifactId )
     {
         return Holder.deref( modelByGA.get( new GAKey( groupId, artifactId ) ) );
     }
 
     static class GAKey
     {
         private final String groupId;
         private final String artifactId;
         private final int hashCode;
 
         GAKey( String groupId, String artifactId )
         {
             this.groupId = groupId;
             this.artifactId = artifactId;
             this.hashCode = Objects.hash( groupId, artifactId );
         }
 
         @Override
         public int hashCode()
         {
             return hashCode;
         }
 
         @Override
         public boolean equals( Object obj )
         {
             if ( this == obj )
             {
                 return true;
             }
             if ( !( obj instanceof GAKey ) )
             {
                 return false;
             }
 
             GAKey other = (GAKey) obj;
             return Objects.equals( artifactId, other.artifactId ) && Objects.equals( groupId, other.groupId );
         }
     }
 }