package org.apache.maven.index.context;
   
   /*
    * 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.io.IOException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.List;
  
  import org.apache.lucene.index.IndexReader;
  import org.apache.lucene.index.MultiReader;
  import org.apache.lucene.search.IndexSearcher;
  
  public class NexusIndexMultiReader
  {
      private final List<IndexingContext> contexts;
  
      private List<IndexSearcher> searchers;
  
      public NexusIndexMultiReader( final Collection<IndexingContext> contexts )
      {
          this.contexts = Collections.unmodifiableList( new ArrayList<IndexingContext>( contexts ) );
      }
  
      public synchronized IndexReader acquire()
          throws IOException
      {
          if ( searchers != null )
          {
              release();
              throw new IllegalStateException( "acquire() called 2nd time without release() in between!" );
          }
          this.searchers = new ArrayList<IndexSearcher>();
          final ArrayList<IndexReader> contextReaders = new ArrayList<IndexReader>( contexts.size() );
          for ( IndexingContext ctx : contexts )
          {
              final IndexSearcher indexSearcher = ctx.acquireIndexSearcher();
              searchers.add( indexSearcher );
              contextReaders.add( indexSearcher.getIndexReader() );
          }
          return new MultiReader( contextReaders.toArray( new IndexReader[contextReaders.size()] ) );
      }
  
      public synchronized void release()
          throws IOException
      {
          if ( searchers != null )
          {
              final Iterator<IndexingContext> ic = contexts.iterator();
              final Iterator<IndexSearcher> is = searchers.iterator();
  
              while ( ic.hasNext() && is.hasNext() )
              {
                  ic.next().releaseIndexSearcher( is.next() );
              }
  
              if ( ic.hasNext() || is.hasNext() )
              {
                  throw new IllegalStateException( "Context and IndexSearcher mismatch: " + contexts + " vs " + searchers );
              }
          }
  
          searchers = null;
      }
  
      /**
       * Watch out with this method, as it's use depends on (if you control it at all) was {@link #acquire()} method
       * invoked at all or not. Returns {@code null} if not, otherwise the list of acquired searchers. Not thread safe.
       * 
       * @return
       */
      public synchronized List<IndexSearcher> getAcquiredSearchers()
      {
          return searchers;
      }
  }