/*
    * 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.
   */
  package org.apache.maven.index.context;
  
  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<>(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<>();
          final ArrayList<IndexReader> contextReaders = new ArrayList<>(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;
      }
  }