/*
 * 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.lucene.search;

import java.io.IOException;
import org.apache.lucene.index.LeafReaderContext;

/**
 * Expert: Collectors are primarily meant to be used to gather raw results from a search, and
 * implement sorting or custom result filtering, collation, etc.
 *
 * <p>Lucene's core collectors are derived from {@link Collector} and {@link SimpleCollector}.
 * Likely your application can use one of these classes, or subclass {@link TopDocsCollector},
 * instead of implementing Collector directly:
 *
 * <ul>
 *   <li>{@link TopDocsCollector} is an abstract base class that assumes you will retrieve the top N
 *       docs, according to some criteria, after collection is done.
 *   <li>{@link TopScoreDocCollector} is a concrete subclass {@link TopDocsCollector} and sorts
 *       according to score + docID. This is used internally by the {@link IndexSearcher} search
 *       methods that do not take an explicit {@link Sort}. It is likely the most frequently used
 *       collector.
 *   <li>{@link TopFieldCollector} subclasses {@link TopDocsCollector} and sorts according to a
 *       specified {@link Sort} object (sort by field). This is used internally by the {@link
 *       IndexSearcher} search methods that take an explicit {@link Sort}.
 *   <li>{@link PositiveScoresOnlyCollector} wraps any other Collector and prevents collection of
 *       hits whose score is &lt;= 0.0
 * </ul>
 *
 * @lucene.experimental
 */
public interface Collector {

  /**
   * Create a new {@link LeafCollector collector} to collect the given context.
   *
   * @param context next atomic reader context
   */
  LeafCollector getLeafCollector(LeafReaderContext context) throws IOException;

  /** Indicates what features are required from the scorer. */
  ScoreMode scoreMode();

  /**
   * Set the {@link Weight} that will be used to produce scorers that will feed {@link
   * LeafCollector}s. This is typically useful to have access to {@link Weight#count} from {@link
   * Collector#getLeafCollector}.
   */
  default void setWeight(Weight weight) {}
}
