/*
 * 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.geode.cache.lucene.internal.distributed;

import java.util.Collection;

import org.apache.geode.cache.lucene.internal.repository.IndexRepository;
import org.apache.geode.cache.lucene.internal.repository.IndexResultCollector;

/**
 * {@link CollectorManager}s create instances of {@link IndexResultCollector} and utility methods to
 * aggregate results collected by individual collectors. The collectors created by this class are
 * primarily used for collecting results from {@link IndexRepository}s. The collectors can also be
 * used for aggregating results of other collectors of same type. Typically search result
 * aggregation is completed in two phases. First at a member level for merging results from local
 * buckets. And then at search coordinator level for merging results from members. Use of same
 * collector in both phases is expected to produce deterministic merge result irrespective of the
 * way buckets are distributed.
 * 
 * @param <C> Type of IndexResultCollector created by this manager
 */
public interface CollectorManager<C extends IndexResultCollector> {
  /**
   * Creates a new collector to store the results of a Lucene query.
   *
   * @param name Name/Identifier for this collector. For e.g. region name/bucketId.
   * @return a new {@link IndexResultCollector}. This must return a different instance on each call.
   *         A new collector would be created for each bucket on a member node.
   */
  C newCollector(String name);

  /**
   * Reduce the results of individual collectors into a meaningful result. This method must be
   * called after collection is finished on all provided collectors.
   *
   * @param results - Collection of the results of a Lucene query execution.
   * @return IndexResultCollector containing a reduced set of the results of the Lucene query.
   * 
   */
  C reduce(Collection<C> results);
}
