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Advanced Spatial Shape Strategies for Apache Lucene
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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.spatial.composite;

import java.io.IOException;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.search.ConstantScoreScorer;
import org.apache.lucene.search.ConstantScoreWeight;
import org.apache.lucene.search.DocIdSet;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.QueryVisitor;
import org.apache.lucene.search.ScoreMode;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.search.TwoPhaseIterator;
import org.apache.lucene.search.Weight;
import org.apache.lucene.spatial.prefix.AbstractVisitingPrefixTreeQuery;
import org.apache.lucene.spatial.prefix.tree.Cell;
import org.apache.lucene.spatial.prefix.tree.SpatialPrefixTree;
import org.apache.lucene.spatial.util.ShapeValuesPredicate;
import org.apache.lucene.util.DocIdSetBuilder;
import org.locationtech.spatial4j.shape.Shape;
import org.locationtech.spatial4j.shape.SpatialRelation;

/**
 * A spatial Intersects predicate that distinguishes an approximated match from an exact match based
 * on which cells are within the query shape. It exposes a {@link TwoPhaseIterator} that will verify
 * a match with a provided predicate in the form of an ShapeValuesPredicate.
 *
 * @lucene.internal
 */
public class IntersectsRPTVerifyQuery extends Query {

  private final IntersectsDifferentiatingQuery intersectsDiffQuery;
  private final ShapeValuesPredicate predicateValueSource;

  public IntersectsRPTVerifyQuery(
      Shape queryShape,
      String fieldName,
      SpatialPrefixTree grid,
      int detailLevel,
      int prefixGridScanLevel,
      ShapeValuesPredicate predicateValueSource) {
    this.predicateValueSource = predicateValueSource;
    this.intersectsDiffQuery =
        new IntersectsDifferentiatingQuery(
            queryShape, fieldName, grid, detailLevel, prefixGridScanLevel);
  }

  @Override
  public String toString(String field) {
    return "IntersectsVerified(fieldName=" + field + ")";
  }

  @Override
  public boolean equals(Object other) {
    return sameClassAs(other) && equalsTo(getClass().cast(other));
  }

  private boolean equalsTo(IntersectsRPTVerifyQuery other) {
    return intersectsDiffQuery.equals(other.intersectsDiffQuery)
        && predicateValueSource.equals(other.predicateValueSource);
  }

  @Override
  public int hashCode() {
    int result = classHash();
    result = 31 * result + intersectsDiffQuery.hashCode();
    result = 31 * result + predicateValueSource.hashCode();
    return result;
  }

  @Override
  public void visit(QueryVisitor visitor) {
    visitor.visitLeaf(this);
  }

  @Override
  public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)
      throws IOException {

    return new ConstantScoreWeight(this, boost) {
      @Override
      public Scorer scorer(LeafReaderContext context) throws IOException {
        // Compute approx & exact
        final IntersectsDifferentiatingQuery.IntersectsDifferentiatingVisitor result =
            intersectsDiffQuery.compute(context);
        if (result.approxDocIdSet == null) {
          return null;
        }
        final DocIdSetIterator approxDISI = result.approxDocIdSet.iterator();
        if (approxDISI == null) {
          return null;
        }
        final DocIdSetIterator exactIterator;
        if (result.exactDocIdSet != null) {
          // If both sets are the same, there's nothing to verify; we needn't return a
          // TwoPhaseIterator
          if (result.approxDocIdSet == result.exactDocIdSet) {
            return new ConstantScoreScorer(this, score(), scoreMode, approxDISI);
          }
          exactIterator = result.exactDocIdSet.iterator();
          assert exactIterator != null;
        } else {
          exactIterator = null;
        }

        final TwoPhaseIterator twoPhaseIterator =
            new TwoPhaseIterator(approxDISI) {

              final TwoPhaseIterator predFuncValues =
                  predicateValueSource.iterator(context, approxDISI);

              @Override
              public boolean matches() throws IOException {
                final int doc = approxDISI.docID();
                if (exactIterator != null) {
                  if (exactIterator.docID() < doc) {
                    exactIterator.advance(doc);
                  }
                  if (exactIterator.docID() == doc) {
                    return true;
                  }
                }
                return predFuncValues.matches();
              }

              @Override
              public float matchCost() {
                return 100; // TODO: use cost of exactIterator.advance() and predFuncValues.cost()
              }
            };

        return new ConstantScoreScorer(this, score(), scoreMode, twoPhaseIterator);
      }

      @Override
      public boolean isCacheable(LeafReaderContext ctx) {
        return predicateValueSource.isCacheable(ctx);
      }
    };
  }

  // This may be a "Query" but we don't use it as-such; the caller calls the constructor and then
  // compute() and examines
  // the results which consists of two parts -- the approximated results, and a subset of exact
  // matches. The
  // difference needs to be verified.
  // TODO refactor AVPTQ to not be a Query?
  private static class IntersectsDifferentiatingQuery extends AbstractVisitingPrefixTreeQuery {

    public IntersectsDifferentiatingQuery(
        Shape queryShape,
        String fieldName,
        SpatialPrefixTree grid,
        int detailLevel,
        int prefixGridScanLevel) {
      super(queryShape, fieldName, grid, detailLevel, prefixGridScanLevel);
    }

    IntersectsDifferentiatingQuery.IntersectsDifferentiatingVisitor compute(
        LeafReaderContext context) throws IOException {
      final IntersectsDifferentiatingQuery.IntersectsDifferentiatingVisitor result =
          new IntersectsDifferentiatingQuery.IntersectsDifferentiatingVisitor(context);
      result.getDocIdSet(); // computes
      return result;
    }

    // TODO consider if IntersectsPrefixTreeQuery should simply do this and provide both sets

    class IntersectsDifferentiatingVisitor extends VisitorTemplate {
      DocIdSetBuilder approxBuilder;
      DocIdSetBuilder exactBuilder;
      boolean approxIsEmpty = true;
      boolean exactIsEmpty = true;
      DocIdSet exactDocIdSet;
      DocIdSet approxDocIdSet;

      public IntersectsDifferentiatingVisitor(LeafReaderContext context) throws IOException {
        super(context);
      }

      @Override
      protected void start() throws IOException {
        approxBuilder = new DocIdSetBuilder(maxDoc, terms);
        exactBuilder = new DocIdSetBuilder(maxDoc, terms);
      }

      @Override
      protected DocIdSet finish() throws IOException {
        if (exactIsEmpty) {
          exactDocIdSet = null;
        } else {
          exactDocIdSet = exactBuilder.build();
        }
        if (approxIsEmpty) {
          approxDocIdSet = exactDocIdSet; // optimization
        } else {
          if (exactDocIdSet != null) {
            approxBuilder.add(exactDocIdSet.iterator());
          }
          approxDocIdSet = approxBuilder.build();
        }
        return null; // unused in this weird re-use of AVPTQ
      }

      @Override
      protected boolean visitPrefix(Cell cell) throws IOException {
        if (cell.getShapeRel() == SpatialRelation.WITHIN) {
          exactIsEmpty = false;
          collectDocs(exactBuilder); // note: we'll add exact to approx on finish()
          return false;
        } else if (cell.getLevel() == detailLevel) {
          approxIsEmpty = false;
          collectDocs(approxBuilder);
          return false;
        }
        return true;
      }

      @Override
      protected void visitLeaf(Cell cell) throws IOException {
        if (cell.getShapeRel() == SpatialRelation.WITHIN) {
          exactIsEmpty = false;
          collectDocs(exactBuilder); // note: we'll add exact to approx on finish()
        } else {
          approxIsEmpty = false;
          collectDocs(approxBuilder);
        }
      }
    }

    @Override
    public DocIdSet getDocIdSet(LeafReaderContext context) throws IOException {
      throw new IllegalStateException();
    }

    @Override
    public String toString(String field) {
      throw new IllegalStateException();
    }
  }
}