/*
 * 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 org.apache.lucene.util.PriorityQueue;

Represents hits returned by IndexSearcher.search(Query, int). /** Represents hits returned by {@link
 * IndexSearcher#search(Query,int)}. */
public class TopDocs {

  
The total number of hits for the query. /** The total number of hits for the query. */
  public TotalHits totalHits;

  
The top hits for the query. /** The top hits for the query. */
  public ScoreDoc[] scoreDocs;

  
Constructs a TopDocs. /** Constructs a TopDocs. */
  public TopDocs(TotalHits totalHits, ScoreDoc[] scoreDocs) {
    this.totalHits = totalHits;
    this.scoreDocs = scoreDocs;
  }

  // Refers to one hit:
  private final static class ShardRef {
    // Which shard (index into shardHits[]):
    final int shardIndex;

    // True if we should use the incoming ScoreDoc.shardIndex for sort order
    final boolean useScoreDocIndex;

    // Which hit within the shard:
    int hitIndex;

    ShardRef(int shardIndex, boolean useScoreDocIndex) {
      this.shardIndex = shardIndex;
      this.useScoreDocIndex = useScoreDocIndex;
    }

    @Override
    public String toString() {
      return "ShardRef(shardIndex=" + shardIndex + " hitIndex=" + hitIndex + ")";
    }

    int getShardIndex(ScoreDoc scoreDoc) {
      if (useScoreDocIndex) {
        if (scoreDoc.shardIndex == -1) {
          throw new IllegalArgumentException("setShardIndex is false but TopDocs[" + shardIndex + "].scoreDocs[" + hitIndex + "] is not set");
        }
        return scoreDoc.shardIndex;
      } else {
        // NOTE: we don't assert that shardIndex is -1 here, because caller could in fact have set it but asked us to ignore it now
        return shardIndex;
      }
    }
  }

  
if we need to tie-break since score / sort value are the same we first compare shard index (lower shard wins)
and then iff shard index is the same we use the hit index.
/**
   * if we need to tie-break since score / sort value are the same we first compare shard index (lower shard wins)
   * and then iff shard index is the same we use the hit index.
   */
  static boolean tieBreakLessThan(ShardRef first, ScoreDoc firstDoc, ShardRef second, ScoreDoc secondDoc) {
    final int firstShardIndex = first.getShardIndex(firstDoc);
    final int secondShardIndex = second.getShardIndex(secondDoc);
    // Tie break: earlier shard wins
    if (firstShardIndex< secondShardIndex) {
      return true;
    } else if (firstShardIndex > secondShardIndex) {
      return false;
    } else {
      // Tie break in same shard: resolve however the
      // shard had resolved it:
      assert first.hitIndex != second.hitIndex;
      return first.hitIndex < second.hitIndex;
    }
  }

  // Specialized MergeSortQueue that just merges by
  // relevance score, descending:
  private static class ScoreMergeSortQueue extends PriorityQueue<ShardRef> {
    final ScoreDoc[][] shardHits;

    public ScoreMergeSortQueue(TopDocs[] shardHits) {
      super(shardHits.length);
      this.shardHits = new ScoreDoc[shardHits.length][];
      for(int shardIDX=0;shardIDX<shardHits.length;shardIDX++) {
        this.shardHits[shardIDX] = shardHits[shardIDX].scoreDocs;
      }
    }

    // Returns true if first is < second
    @Override
    public boolean lessThan(ShardRef first, ShardRef second) {
      assert first != second;
      ScoreDoc firstScoreDoc = shardHits[first.shardIndex][first.hitIndex];
      ScoreDoc secondScoreDoc = shardHits[second.shardIndex][second.hitIndex];
      if (firstScoreDoc.score < secondScoreDoc.score) {
        return false;
      } else if (firstScoreDoc.score > secondScoreDoc.score) {
        return true;
      } else {
        return tieBreakLessThan(first, firstScoreDoc, second, secondScoreDoc);
      }
    }
  }

  @SuppressWarnings({"rawtypes","unchecked"})
  private static class MergeSortQueue extends PriorityQueue<ShardRef> {
    // These are really FieldDoc instances:
    final ScoreDoc[][] shardHits;
    final FieldComparator<?>[] comparators;
    final int[] reverseMul;

    public MergeSortQueue(Sort sort, TopDocs[] shardHits) {
      super(shardHits.length);
      this.shardHits = new ScoreDoc[shardHits.length][];
      for(int shardIDX=0;shardIDX<shardHits.length;shardIDX++) {
        final ScoreDoc[] shard = shardHits[shardIDX].scoreDocs;
        //System.out.println("  init shardIdx=" + shardIDX + " hits=" + shard);
        if (shard != null) {
          this.shardHits[shardIDX] = shard;
          // Fail gracefully if API is misused:
          for(int hitIDX=0;hitIDX<shard.length;hitIDX++) {
            final ScoreDoc sd = shard[hitIDX];
            if (!(sd instanceof FieldDoc)) {
              throw new IllegalArgumentException("shard " + shardIDX + " was not sorted by the provided Sort (expected FieldDoc but got ScoreDoc)");
            }
            final FieldDoc fd = (FieldDoc) sd;
            if (fd.fields == null) {
              throw new IllegalArgumentException("shard " + shardIDX + " did not set sort field values (FieldDoc.fields is null)");
            }
          }
        }
      }

      final SortField[] sortFields = sort.getSort();
      comparators = new FieldComparator[sortFields.length];
      reverseMul = new int[sortFields.length];
      for(int compIDX=0;compIDX<sortFields.length;compIDX++) {
        final SortField sortField = sortFields[compIDX];
        comparators[compIDX] = sortField.getComparator(1, compIDX);
        reverseMul[compIDX] = sortField.getReverse() ? -1 : 1;
      }
    }

    // Returns true if first is < second
    @Override
    public boolean lessThan(ShardRef first, ShardRef second) {
      assert first != second;
      final FieldDoc firstFD = (FieldDoc) shardHits[first.shardIndex][first.hitIndex];
      final FieldDoc secondFD = (FieldDoc) shardHits[second.shardIndex][second.hitIndex];
      //System.out.println("  lessThan:\n     first=" + first + " doc=" + firstFD.doc + " score=" + firstFD.score + "\n    second=" + second + " doc=" + secondFD.doc + " score=" + secondFD.score);

      for(int compIDX=0;compIDX<comparators.length;compIDX++) {
        final FieldComparator comp = comparators[compIDX];
        //System.out.println("    cmp idx=" + compIDX + " cmp1=" + firstFD.fields[compIDX] + " cmp2=" + secondFD.fields[compIDX] + " reverse=" + reverseMul[compIDX]);

        final int cmp = reverseMul[compIDX] * comp.compareValues(firstFD.fields[compIDX], secondFD.fields[compIDX]);
        
        if (cmp != 0) {
          //System.out.println("    return " + (cmp < 0));
          return cmp < 0;
        }
      }
      return tieBreakLessThan(first, firstFD, second, secondFD);
    }
  }

  
Returns a new TopDocs, containing topN results across the provided TopDocs, sorting by score. Each TopDocs instance must be sorted. @see #merge(int, int, TopDocs[], boolean) @lucene.experimental /** Returns a new TopDocs, containing topN results across
   *  the provided TopDocs, sorting by score. Each {@link TopDocs}
   *  instance must be sorted.
   *
   *  @see #merge(int, int, TopDocs[], boolean)
   *  @lucene.experimental */
  public static TopDocs merge(int topN, TopDocs[] shardHits) {
    return merge(0, topN, shardHits, true);
  }

  
Same as merge(int, TopDocs[]) but also ignores the top start top docs. This is typically useful for pagination. Note: If setShardIndex is true, this method will assume the incoming order of shardHits reflects each shard's index and will fill the ScoreDoc.shardIndex, otherwise it must already be set for all incoming ScoreDocs, which can be useful when doing multiple reductions (merges) of TopDocs. 
@lucene.experimental
/**
   * Same as {@link #merge(int, TopDocs[])} but also ignores the top
   * {@code start} top docs. This is typically useful for pagination.
   *
   * Note: If {@code setShardIndex} is true, this method will assume the incoming order of {@code shardHits} reflects
   * each shard's index and will fill the {@link ScoreDoc#shardIndex}, otherwise
   * it must already be set for all incoming {@code ScoreDoc}s, which can be useful when doing multiple reductions
   * (merges) of TopDocs.
   *
   * @lucene.experimental
   */
  public static TopDocs merge(int start, int topN, TopDocs[] shardHits, boolean setShardIndex) {
    return mergeAux(null, start, topN, shardHits, setShardIndex);
  }

  
Returns a new TopFieldDocs, containing topN results across the provided TopFieldDocs, sorting by the specified Sort. Each of the TopDocs must have been sorted by the same Sort, and sort field values must have been filled (ie, fillFields=true must be passed to TopFieldCollector.create). @see #merge(Sort, int, int, TopFieldDocs[], boolean) 
@lucene.experimental
/** Returns a new TopFieldDocs, containing topN results across
   *  the provided TopFieldDocs, sorting by the specified {@link
   *  Sort}.  Each of the TopDocs must have been sorted by
   *  the same Sort, and sort field values must have been
   *  filled (ie, <code>fillFields=true</code> must be
   *  passed to {@link TopFieldCollector#create}).
   *  @see #merge(Sort, int, int, TopFieldDocs[], boolean)
   * @lucene.experimental */
  public static TopFieldDocs merge(Sort sort, int topN, TopFieldDocs[] shardHits) {
    return merge(sort, 0, topN, shardHits, true);
  }

  
Same as merge(Sort, int, TopFieldDocs[]) but also ignores the top start top docs. This is typically useful for pagination. Note: If setShardIndex is true, this method will assume the incoming order of shardHits reflects each shard's index and will fill the ScoreDoc.shardIndex, otherwise it must already be set for all incoming ScoreDocs, which can be useful when doing multiple reductions (merges) of TopDocs. 
@lucene.experimental
/**
   * Same as {@link #merge(Sort, int, TopFieldDocs[])} but also ignores the top
   * {@code start} top docs. This is typically useful for pagination.
   *
   * Note: If {@code setShardIndex} is true, this method will assume the incoming order of {@code shardHits} reflects
   * each shard's index and will fill the {@link ScoreDoc#shardIndex}, otherwise
   * it must already be set for all incoming {@code ScoreDoc}s, which can be useful when doing multiple reductions
   * (merges) of TopDocs.
   *
   * @lucene.experimental
   */
  public static TopFieldDocs merge(Sort sort, int start, int topN, TopFieldDocs[] shardHits, boolean setShardIndex) {
    if (sort == null) {
      throw new IllegalArgumentException("sort must be non-null when merging field-docs");
    }
    return (TopFieldDocs) mergeAux(sort, start, topN, shardHits, setShardIndex);
  }

  
Auxiliary method used by the merge impls. A sort value of null is used to indicate that docs should be sorted by score. /** Auxiliary method used by the {@link #merge} impls. A sort value of null
   *  is used to indicate that docs should be sorted by score. */
  private static TopDocs mergeAux(Sort sort, int start, int size, TopDocs[] shardHits, boolean setShardIndex) {

    final PriorityQueue<ShardRef> queue;
    if (sort == null) {
      queue = new ScoreMergeSortQueue(shardHits);
    } else {
      queue = new MergeSortQueue(sort, shardHits);
    }

    long totalHitCount = 0;
    TotalHits.Relation totalHitsRelation = TotalHits.Relation.EQUAL_TO;
    int availHitCount = 0;
    for(int shardIDX=0;shardIDX<shardHits.length;shardIDX++) {
      final TopDocs shard = shardHits[shardIDX];
      // totalHits can be non-zero even if no hits were
      // collected, when searchAfter was used:
      totalHitCount += shard.totalHits.value;
      // If any hit count is a lower bound then the merged
      // total hit count is a lower bound as well
      if (shard.totalHits.relation == TotalHits.Relation.GREATER_THAN_OR_EQUAL_TO) {
        totalHitsRelation = TotalHits.Relation.GREATER_THAN_OR_EQUAL_TO;
      }
      if (shard.scoreDocs != null && shard.scoreDocs.length > 0) {
        availHitCount += shard.scoreDocs.length;
        queue.add(new ShardRef(shardIDX, setShardIndex == false));
      }
    }

    final ScoreDoc[] hits;
    if (availHitCount <= start) {
      hits = new ScoreDoc[0];
    } else {
      hits = new ScoreDoc[Math.min(size, availHitCount - start)];
      int requestedResultWindow = start + size;
      int numIterOnHits = Math.min(availHitCount, requestedResultWindow);
      int hitUpto = 0;
      while (hitUpto < numIterOnHits) {
        assert queue.size() > 0;
        ShardRef ref = queue.top();
        final ScoreDoc hit = shardHits[ref.shardIndex].scoreDocs[ref.hitIndex++];
        if (setShardIndex) {
          // caller asked us to record shardIndex (index of the TopDocs array) this hit is coming from:
          hit.shardIndex = ref.shardIndex;
        } else if (hit.shardIndex == -1) {
          throw new IllegalArgumentException("setShardIndex is false but TopDocs[" + ref.shardIndex + "].scoreDocs[" + (ref.hitIndex-1) + "] is not set");
        }
          
        if (hitUpto >= start) {
          hits[hitUpto - start] = hit;
        }

        hitUpto++;

        if (ref.hitIndex < shardHits[ref.shardIndex].scoreDocs.length) {
          // Not done with this these TopDocs yet:
          queue.updateTop();
        } else {
          queue.pop();
        }
      }
    }

    TotalHits totalHits = new TotalHits(totalHitCount, totalHitsRelation);
    if (sort == null) {
      return new TopDocs(totalHits, hits);
    } else {
      return new TopFieldDocs(totalHits, hits, sort.getSort());
    }
  }
}