/*
 * 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 java.util.ArrayList;
import java.util.Collection;

/** A Scorer for queries with a required part and an optional part.
 * Delays skipTo() on the optional part until a score() is needed.
 */
class ReqOptSumScorer extends Scorer {
  /** The scorers passed from the constructor.
   * These are set to null as soon as their next() or skipTo() returns false.
   */
  protected final Scorer reqScorer;
  protected final Scorer optScorer;
  protected final DocIdSetIterator optIterator;

  /** Construct a <code>ReqOptScorer</code>.
   * @param reqScorer The required scorer. This must match.
   * @param optScorer The optional scorer. This is used for scoring only.
   */
  public ReqOptSumScorer(
      Scorer reqScorer,
      Scorer optScorer)
  {
    super(reqScorer.weight);
    assert reqScorer != null;
    assert optScorer != null;
    this.reqScorer = reqScorer;
    this.optScorer = optScorer;
    this.optIterator = optScorer.iterator();
  }

  @Override
  public TwoPhaseIterator twoPhaseIterator() {
    return reqScorer.twoPhaseIterator();
  }

  @Override
  public DocIdSetIterator iterator() {
    return reqScorer.iterator();
  }

  @Override
  public int docID() {
    return reqScorer.docID();
  }

  /** Returns the score of the current document matching the query.
   * Initially invalid, until the {@link #iterator()} is advanced the first time.
   * @return The score of the required scorer, eventually increased by the score
   * of the optional scorer when it also matches the current document.
   */
  @Override
  public float score() throws IOException {
    // TODO: sum into a double and cast to float if we ever send required clauses to BS1
    int curDoc = reqScorer.docID();
    float score = reqScorer.score();

    int optScorerDoc = optIterator.docID();
    if (optScorerDoc < curDoc) {
      optScorerDoc = optIterator.advance(curDoc);
    }
    
    if (optScorerDoc == curDoc) {
      score += optScorer.score();
    }
    
    return score;
  }

  @Override
  public int freq() throws IOException {
    // we might have deferred advance()
    score();
    return optIterator.docID() == reqScorer.docID() ? 2 : 1;
  }

  @Override
  public Collection<ChildScorer> getChildren() {
    ArrayList<ChildScorer> children = new ArrayList<>(2);
    children.add(new ChildScorer(reqScorer, "MUST"));
    children.add(new ChildScorer(optScorer, "SHOULD"));
    return children;
  }

}