/*
 * 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.geopoint.search;

import java.io.IOException;

import org.apache.lucene.index.LeafReader;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.PostingsEnum;
import org.apache.lucene.index.SortedNumericDocValues;
import org.apache.lucene.index.Terms;
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.Scorer;
import org.apache.lucene.search.TwoPhaseIterator;
import org.apache.lucene.search.Weight;
import org.apache.lucene.spatial.geopoint.document.GeoPointField;
import org.apache.lucene.util.BitSet;
import org.apache.lucene.util.DocIdSetBuilder;
import org.apache.lucene.util.FixedBitSet;
import org.apache.lucene.util.SparseFixedBitSet;

/**
 * Custom ConstantScoreWrapper for {@code GeoPointMultiTermQuery} that cuts over to DocValues
 * for post filtering boundary ranges. Multi-valued GeoPoint documents are supported.
 *
 * @lucene.experimental
 */
final class GeoPointTermQueryConstantScoreWrapper <Q extends GeoPointMultiTermQuery> extends Query {
  protected final Q query;

  protected GeoPointTermQueryConstantScoreWrapper(Q query) {
    this.query = query;
  }

  /**
   * Returns the encapsulated query.
   */
  public Q getQuery() {
    return query;
  }

  @Override
  public String toString(String field) {
    return query.toString();
  }

  @Override
  public final boolean equals(final Object other) {
    return sameClassAs(other) &&
           query.equals(((GeoPointTermQueryConstantScoreWrapper<?>) other).query);
  }

  @Override
  public final int hashCode() {
    return 31 * classHash() + query.hashCode();
  }

  @Override
  public Weight createWeight(IndexSearcher searcher, boolean needsScores, float boost) throws IOException {
    return new ConstantScoreWeight(this, boost) {

      @Override
      public Scorer scorer(LeafReaderContext context) throws IOException {
        final Terms terms = context.reader().terms(query.getField());
        if (terms == null) {
          return null;
        }

        final GeoPointTermsEnum termsEnum = (GeoPointTermsEnum)(query.getTermsEnum(terms, null));
        assert termsEnum != null;

        LeafReader reader = context.reader();
        // approximation (postfiltering has not yet been applied)
        DocIdSetBuilder builder = new DocIdSetBuilder(reader.maxDoc(), terms);
        // subset of documents that need no postfiltering, this is purely an optimization
        final BitSet preApproved;
        // dumb heuristic: if the field is really sparse, use a sparse impl
        if (terms.getDocCount() * 100L < reader.maxDoc()) {
          preApproved = new SparseFixedBitSet(reader.maxDoc());
        } else {
          preApproved = new FixedBitSet(reader.maxDoc());
        }
        PostingsEnum docs = null;

        while (termsEnum.next() != null) {
          docs = termsEnum.postings(docs, PostingsEnum.NONE);
          // boundary terms need post filtering
          if (termsEnum.boundaryTerm()) {
            builder.add(docs);
          } else {
            int numDocs = termsEnum.docFreq();
            DocIdSetBuilder.BulkAdder adder = builder.grow(numDocs);
            for (int i = 0; i < numDocs; ++i) {
              int docId = docs.nextDoc();
              adder.add(docId);
              preApproved.set(docId);
            }
          }
        }

        DocIdSet set = builder.build();
        final DocIdSetIterator disi = set.iterator();
        if (disi == null) {
          return null;
        }

        // return two-phase iterator using docvalues to postfilter candidates
        SortedNumericDocValues sdv = reader.getSortedNumericDocValues(query.getField());
        TwoPhaseIterator iterator = new TwoPhaseIterator(disi) {
          @Override
          public boolean matches() throws IOException {
            int docId = disi.docID();
            if (preApproved.get(docId)) {
              return true;
            } else {
              if (docId > sdv.docID()) {
                sdv.advance(docId);
              }
              if (docId == sdv.docID()) {
                int count = sdv.docValueCount();
                for (int i = 0; i < count; i++) {
                  long hash = sdv.nextValue();
                  if (termsEnum.postFilter(GeoPointField.decodeLatitude(hash), GeoPointField.decodeLongitude(hash))) {
                    return true;
                  }
                }
              }
              return false;
            }
          }

          @Override
          public float matchCost() {
            return 20; // TODO: make this fancier
          }
        };
        return new ConstantScoreScorer(this, score(), iterator);
      }
    };
  }
}