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/*
 * 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.util.concurrent.atomic.AtomicLong;

/**
 * Used for defining custom algorithms to allow searches to early terminate
 */
abstract class HitsThresholdChecker {
  /**
   * Implementation of HitsThresholdChecker which allows global hit counting
   */
  private static class GlobalHitsThresholdChecker extends HitsThresholdChecker {
    private final int totalHitsThreshold;
    private final AtomicLong globalHitCount;

    public GlobalHitsThresholdChecker(int totalHitsThreshold) {

      if (totalHitsThreshold < 0) {
        throw new IllegalArgumentException("totalHitsThreshold must be >= 0, got " + totalHitsThreshold);
      }

      this.totalHitsThreshold = totalHitsThreshold;
      this.globalHitCount = new AtomicLong();
    }

    @Override
    public void incrementHitCount() {
      globalHitCount.incrementAndGet();
    }

    @Override
    public boolean isThresholdReached(){
      return globalHitCount.get() > totalHitsThreshold;
    }

    @Override
    public ScoreMode scoreMode() {
      return totalHitsThreshold == Integer.MAX_VALUE ? ScoreMode.COMPLETE : ScoreMode.TOP_SCORES;
    }

    @Override
    public int getHitsThreshold() {
      return totalHitsThreshold;
    }
  }

  /**
   * Default implementation of HitsThresholdChecker to be used for single threaded execution
   */
  private static class LocalHitsThresholdChecker extends HitsThresholdChecker {
    private final int totalHitsThreshold;
    private int hitCount;

    public LocalHitsThresholdChecker(int totalHitsThreshold) {

      if (totalHitsThreshold < 0) {
        throw new IllegalArgumentException("totalHitsThreshold must be >= 0, got " + totalHitsThreshold);
      }

      this.totalHitsThreshold = totalHitsThreshold;
    }

    @Override
    public void incrementHitCount() {
      ++hitCount;
    }

    @Override
    public boolean isThresholdReached() {
      return hitCount > totalHitsThreshold;
    }

    @Override
    public ScoreMode scoreMode() {
      return totalHitsThreshold == Integer.MAX_VALUE ? ScoreMode.COMPLETE : ScoreMode.TOP_SCORES;
    }

    @Override
    public int getHitsThreshold() {
      return totalHitsThreshold;
    }
  }

  /*
   * Returns a threshold checker that is useful for single threaded searches
   */
  public static HitsThresholdChecker create(final int totalHitsThreshold) {
    return new LocalHitsThresholdChecker(totalHitsThreshold);
  }

  /*
   * Returns a threshold checker that is based on a shared counter
   */
  public static HitsThresholdChecker createShared(final int totalHitsThreshold) {
    return new GlobalHitsThresholdChecker(totalHitsThreshold);
  }

  public abstract void incrementHitCount();
  public abstract ScoreMode scoreMode();
  public abstract int getHitsThreshold();
  public abstract boolean isThresholdReached();
}