/*
 * 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.util.Bits;

/**
 * This class is used to score a range of documents at once, and is returned by {@link
 * Weight#bulkScorer}. Only queries that have a more optimized means of scoring across a range of
 * documents need to override this. Otherwise, a default implementation is wrapped around the {@link
 * Scorer} returned by {@link Weight#scorer}.
 */
public abstract class BulkScorer {

  /**
   * Scores and collects all matching documents.
   *
   * @param collector The collector to which all matching documents are passed.
   * @param acceptDocs {@link Bits} that represents the allowed documents to match, or {@code null}
   *     if they are all allowed to match.
   */
  public void score(LeafCollector collector, Bits acceptDocs) throws IOException {
    final int next = score(collector, acceptDocs, 0, DocIdSetIterator.NO_MORE_DOCS);
    assert next == DocIdSetIterator.NO_MORE_DOCS;
  }

  /**
   * Collects matching documents in a range and return an estimation of the next matching document
   * which is on or after {@code max}.
   *
   * <p>The return value must be:
   *
   * <ul>
   *   <li>&gt;= {@code max},
   *   <li>{@link DocIdSetIterator#NO_MORE_DOCS} if there are no more matches,
   *   <li>&lt;= the first matching document that is &gt;= {@code max} otherwise.
   * </ul>
   *
   * <p>{@code min} is the minimum document to be considered for matching. All documents strictly
   * before this value must be ignored.
   *
   * <p>Although {@code max} would be a legal return value for this method, higher values might help
   * callers skip more efficiently over non-matching portions of the docID space.
   *
   * <p>For instance, a {@link Scorer}-based implementation could look like below:
   *
   * <pre class="prettyprint">
   * private final Scorer scorer; // set via constructor
   *
   * public int score(LeafCollector collector, Bits acceptDocs, int min, int max) throws IOException {
   *   collector.setScorer(scorer);
   *   int doc = scorer.docID();
   *   if (doc &lt; min) {
   *     doc = scorer.advance(min);
   *   }
   *   while (doc &lt; max) {
   *     if (acceptDocs == null || acceptDocs.get(doc)) {
   *       collector.collect(doc);
   *     }
   *     doc = scorer.nextDoc();
   *   }
   *   return doc;
   * }
   * </pre>
   *
   * @param collector The collector to which all matching documents are passed.
   * @param acceptDocs {@link Bits} that represents the allowed documents to match, or {@code null}
   *     if they are all allowed to match.
   * @param min Score starting at, including, this document
   * @param max Score up to, but not including, this doc
   * @return an under-estimation of the next matching doc after max
   */
  public abstract int score(LeafCollector collector, Bits acceptDocs, int min, int max)
      throws IOException;

  /** Same as {@link DocIdSetIterator#cost()} for bulk scorers. */
  public abstract long cost();
}
