https://lucene.apache.org/lucene-parent/lucene-core: Apache Lucene Java Core (The Apache Software Foundation) 
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 * 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.
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package org.apache.lucene.index;

import java.io.IOException;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

import org.apache.lucene.search.FieldComparator;
import org.apache.lucene.search.SortField;
import org.apache.lucene.util.LongValues;
import org.apache.lucene.util.NumericUtils;
import org.apache.lucene.util.packed.PackedInts;

import static org.apache.lucene.search.DocIdSetIterator.NO_MORE_DOCS;


Handles how documents should be sorted in an index, both within a segment and between segments. Implementers must provide the following methods: getDocComparator(LeafReader, int) - an object that determines how documents within a segment are to be sorted getComparableProviders(List<? extends LeafReader>) - an array of objects that return a sortable long value per document and segment getProviderName() - the SPI-registered name of a SortFieldProvider to serialize the sort The companion SortFieldProvider should be registered with SPI via META-INF/services 
/**
 * Handles how documents should be sorted in an index, both within a segment and between
 * segments.
 *
 * Implementers must provide the following methods:
 * {@link #getDocComparator(LeafReader,int)} - an object that determines how documents within a segment are to be sorted
 * {@link #getComparableProviders(List)} - an array of objects that return a sortable long value per document and segment
 * {@link #getProviderName()} - the SPI-registered name of a {@link SortFieldProvider} to serialize the sort
 *
 * The companion {@link SortFieldProvider} should be registered with SPI via {@code META-INF/services}
 */
public interface IndexSorter {

  
Used for sorting documents across segments 
/** Used for sorting documents across segments */
  interface ComparableProvider {
    
Returns a long so that the natural ordering of long values matches the
ordering of doc IDs for the given comparator

/**
     * Returns a long so that the natural ordering of long values matches the
     * ordering of doc IDs for the given comparator
     */
    long getAsComparableLong(int docID) throws IOException;
  }

  
A comparator of doc IDs, used for sorting documents within a segment 
/** A comparator of doc IDs, used for sorting documents within a segment */
  interface DocComparator {
    
Compare docID1 against docID2. The contract for the return value is the same as Comparator.compare(Object, Object). 
/** Compare docID1 against docID2. The contract for the return value is the
     *  same as {@link Comparator#compare(Object, Object)}. */
    int compare(int docID1, int docID2);
  }

  
Get an array of ComparableProvider, one per segment, for merge sorting documents in different segments 
Params:
  • readers – the readers to be merged
/**
   * Get an array of {@link ComparableProvider}, one per segment, for merge sorting documents in different segments
   * @param readers the readers to be merged
   */
  ComparableProvider[] getComparableProviders(List<? extends LeafReader> readers) throws IOException;

  
Get a comparator that determines the sort order of docs within a single Reader. NB We cannot simply use the FieldComparator API because it requires docIDs to be sent in-order. The default implementations allocate array[maxDoc] to hold native values for comparison, but 1) they are transient (only alive while sorting this one segment) and 2) in the typical index sorting case, they are only used to sort newly flushed segments, which will be smaller than merged segments 
Params:
  • reader – the Reader to sort
  • maxDoc – the number of documents in the Reader
/**
   * Get a comparator that determines the sort order of docs within a single Reader.
   *
   * NB We cannot simply use the {@link FieldComparator} API because it requires docIDs to be sent
   * in-order. The default implementations allocate array[maxDoc] to hold native values for comparison,
   * but 1) they are transient (only alive while sorting this one segment) and 2) in the typical
   * index sorting case, they are only used to sort newly flushed segments, which will be smaller
   * than merged segments
   *
   * @param reader the Reader to sort
   * @param maxDoc the number of documents in the Reader
   */
  DocComparator getDocComparator(LeafReader reader, int maxDoc) throws IOException;

  
The SPI-registered name of a SortFieldProvider that will deserialize the parent SortField 
/**
   * The SPI-registered name of a {@link SortFieldProvider} that will deserialize the parent SortField
   */
  String getProviderName();

  
Provide a NumericDocValues instance for a LeafReader

/**
   * Provide a NumericDocValues instance for a LeafReader
   */
  interface NumericDocValuesProvider {
    
Returns the NumericDocValues instance for this LeafReader

/**
     * Returns the NumericDocValues instance for this LeafReader
     */
    NumericDocValues get(LeafReader reader) throws IOException;
  }

  
Provide a SortedDocValues instance for a LeafReader

/**
   * Provide a SortedDocValues instance for a LeafReader
   */
  interface SortedDocValuesProvider {
    
Returns the SortedDocValues instance for this LeafReader

/**
     * Returns the SortedDocValues instance for this LeafReader
     */
    SortedDocValues get(LeafReader reader) throws IOException;
  }

  
Sorts documents based on integer values from a NumericDocValues instance

/**
   * Sorts documents based on integer values from a NumericDocValues instance
   */
  final class IntSorter implements IndexSorter {

    private final Integer missingValue;
    private final int reverseMul;
    private final NumericDocValuesProvider valuesProvider;
    private final String providerName;

    
Creates a new IntSorter

/**
     * Creates a new IntSorter
     */
    public IntSorter(String providerName, Integer missingValue, boolean reverse, NumericDocValuesProvider valuesProvider) {
      this.missingValue = missingValue;
      this.reverseMul = reverse ? -1 : 1;
      this.valuesProvider = valuesProvider;
      this.providerName = providerName;
    }

    @Override
    public ComparableProvider[] getComparableProviders(List<? extends LeafReader> readers) throws IOException {
      ComparableProvider[] providers = new ComparableProvider[readers.size()];
      final long missingValue;
      if (this.missingValue != null) {
        missingValue = this.missingValue;
      } else {
        missingValue = 0L;
      }

      for(int readerIndex=0;readerIndex<readers.size();readerIndex++) {
        final NumericDocValues values = valuesProvider.get(readers.get(readerIndex));

        providers[readerIndex] = docID -> {
          if (values.advanceExact(docID)) {
            return values.longValue();
          } else {
            return missingValue;
          }
        };
      }
      return providers;
    }

    @Override
    public DocComparator getDocComparator(LeafReader reader, int maxDoc) throws IOException {
      final NumericDocValues dvs = valuesProvider.get(reader);
      int[] values = new int[maxDoc];
      if (this.missingValue != null) {
        Arrays.fill(values, this.missingValue);
      }
      while (true) {
        int docID = dvs.nextDoc();
        if (docID == NO_MORE_DOCS) {
          break;
        }
        values[docID] = (int) dvs.longValue();
      }

      return (docID1, docID2) -> reverseMul * Integer.compare(values[docID1], values[docID2]);
    }

    @Override
    public String getProviderName() {
      return providerName;
    }
  }

  
Sorts documents based on long values from a NumericDocValues instance

/**
   * Sorts documents based on long values from a NumericDocValues instance
   */
  final class LongSorter implements IndexSorter {

    private final String providerName;
    private final Long missingValue;
    private final int reverseMul;
    private final NumericDocValuesProvider valuesProvider;

    
Creates a new LongSorter 
/** Creates a new LongSorter */
    public LongSorter(String providerName, Long missingValue, boolean reverse, NumericDocValuesProvider valuesProvider) {
      this.providerName = providerName;
      this.missingValue = missingValue;
      this.reverseMul = reverse ? -1 : 1;
      this.valuesProvider = valuesProvider;
    }

    @Override
    public ComparableProvider[] getComparableProviders(List<? extends LeafReader> readers) throws IOException {
      ComparableProvider[] providers = new ComparableProvider[readers.size()];
      final long missingValue;
      if (this.missingValue != null) {
        missingValue = this.missingValue;
      } else {
        missingValue = 0L;
      }

      for(int readerIndex=0;readerIndex<readers.size();readerIndex++) {
        final NumericDocValues values = valuesProvider.get(readers.get(readerIndex));

        providers[readerIndex] = docID -> {
          if (values.advanceExact(docID)) {
            return values.longValue();
          } else {
            return missingValue;
          }
        };
      }
      return providers;
    }

    @Override
    public DocComparator getDocComparator(LeafReader reader, int maxDoc) throws IOException {
      final NumericDocValues dvs = valuesProvider.get(reader);
      long[] values = new long[maxDoc];
      if (this.missingValue != null) {
        Arrays.fill(values, this.missingValue);
      }
      while (true) {
        int docID = dvs.nextDoc();
        if (docID == NO_MORE_DOCS) {
          break;
        }
        values[docID] = dvs.longValue();
      }

      return (docID1, docID2) -> reverseMul * Long.compare(values[docID1], values[docID2]);
    }

    @Override
    public String getProviderName() {
      return providerName;
    }
  }

  
Sorts documents based on float values from a NumericDocValues instance

/**
   * Sorts documents based on float values from a NumericDocValues instance
   */
  final class FloatSorter implements IndexSorter {

    private final String providerName;
    private final Float missingValue;
    private final int reverseMul;
    private final NumericDocValuesProvider valuesProvider;

    
Creates a new FloatSorter 
/** Creates a new FloatSorter */
    public FloatSorter(String providerName, Float missingValue, boolean reverse, NumericDocValuesProvider valuesProvider) {
      this.providerName = providerName;
      this.missingValue = missingValue;
      this.reverseMul = reverse ? -1 : 1;
      this.valuesProvider = valuesProvider;
    }

    @Override
    public ComparableProvider[] getComparableProviders(List<? extends LeafReader> readers) throws IOException {
      ComparableProvider[] providers = new ComparableProvider[readers.size()];
      final float missingValue;
      if (this.missingValue != null) {
        missingValue = this.missingValue;
      } else {
        missingValue = 0.0f;
      }

      for(int readerIndex=0;readerIndex<readers.size();readerIndex++) {
        final NumericDocValues values = valuesProvider.get(readers.get(readerIndex));

        providers[readerIndex] = docID -> {
          float value = missingValue;
          if (values.advanceExact(docID)) {
            value = Float.intBitsToFloat((int) values.longValue());
          }
          return NumericUtils.floatToSortableInt(value);
        };
      }
      return providers;
    }

    @Override
    public DocComparator getDocComparator(LeafReader reader, int maxDoc) throws IOException {
      final NumericDocValues dvs = valuesProvider.get(reader);
      float[] values = new float[maxDoc];
      if (this.missingValue != null) {
        Arrays.fill(values, this.missingValue);
      }
      while (true) {
        int docID = dvs.nextDoc();
        if (docID == NO_MORE_DOCS) {
          break;
        }
        values[docID] = Float.intBitsToFloat((int) dvs.longValue());
      }

      return (docID1, docID2) -> reverseMul * Float.compare(values[docID1], values[docID2]);
    }

    @Override
    public String getProviderName() {
      return providerName;
    }
  }

  
Sorts documents based on double values from a NumericDocValues instance

/**
   * Sorts documents based on double values from a NumericDocValues instance
   */
  final class DoubleSorter implements IndexSorter {

    private final String providerName;
    private final Double missingValue;
    private final int reverseMul;
    private final NumericDocValuesProvider valuesProvider;

    
Creates a new DoubleSorter 
/** Creates a new DoubleSorter */
    public DoubleSorter(String providerName, Double missingValue, boolean reverse, NumericDocValuesProvider valuesProvider) {
      this.providerName = providerName;
      this.missingValue = missingValue;
      this.reverseMul = reverse ? -1 : 1;
      this.valuesProvider = valuesProvider;
    }

    @Override
    public ComparableProvider[] getComparableProviders(List<? extends LeafReader> readers) throws IOException {
      ComparableProvider[] providers = new ComparableProvider[readers.size()];
      final double missingValue;
      if (this.missingValue != null) {
        missingValue = this.missingValue;
      } else {
        missingValue = 0.0f;
      }

      for(int readerIndex=0;readerIndex<readers.size();readerIndex++) {
        final NumericDocValues values = valuesProvider.get(readers.get(readerIndex));

        providers[readerIndex] = docID -> {
          double value = missingValue;
          if (values.advanceExact(docID)) {
            value = Double.longBitsToDouble(values.longValue());
          }
          return NumericUtils.doubleToSortableLong(value);
        };
      }
      return providers;
    }

    @Override
    public DocComparator getDocComparator(LeafReader reader, int maxDoc) throws IOException {
      final NumericDocValues dvs = valuesProvider.get(reader);
      double[] values = new double[maxDoc];
      if (missingValue != null) {
        Arrays.fill(values, missingValue);
      }
      while (true) {
        int docID = dvs.nextDoc();
        if (docID == NO_MORE_DOCS) {
          break;
        }
        values[docID] = Double.longBitsToDouble(dvs.longValue());
      }

      return (docID1, docID2) -> reverseMul * Double.compare(values[docID1], values[docID2]);
    }

    @Override
    public String getProviderName() {
      return providerName;
    }
  }

  
Sorts documents based on terms from a SortedDocValues instance

/**
   * Sorts documents based on terms from a SortedDocValues instance
   */
  final class StringSorter implements IndexSorter {

    private final String providerName;
    private final Object missingValue;
    private final int reverseMul;
    private final SortedDocValuesProvider valuesProvider;

    
Creates a new StringSorter 
/** Creates a new StringSorter */
    public StringSorter(String providerName, Object missingValue, boolean reverse, SortedDocValuesProvider valuesProvider) {
      this.providerName = providerName;
      this.missingValue = missingValue;
      this.reverseMul = reverse ? -1 : 1;
      this.valuesProvider = valuesProvider;
    }

    @Override
    public ComparableProvider[] getComparableProviders(List<? extends LeafReader> readers) throws IOException {
      final ComparableProvider[] providers = new ComparableProvider[readers.size()];
      final SortedDocValues[] values = new SortedDocValues[readers.size()];
      for(int i=0;i<readers.size();i++) {
        final SortedDocValues sorted = valuesProvider.get(readers.get(i));
        values[i] = sorted;
      }
      OrdinalMap ordinalMap = OrdinalMap.build(null, values, PackedInts.DEFAULT);
      final int missingOrd;
      if (missingValue == SortField.STRING_LAST) {
        missingOrd = Integer.MAX_VALUE;
      } else {
        missingOrd = Integer.MIN_VALUE;
      }

      for(int readerIndex=0;readerIndex<readers.size();readerIndex++) {
        final SortedDocValues readerValues = values[readerIndex];
        final LongValues globalOrds = ordinalMap.getGlobalOrds(readerIndex);
        providers[readerIndex] = docID -> {
          if (readerValues.advanceExact(docID)) {
            // translate segment's ord to global ord space:
            return globalOrds.get(readerValues.ordValue());
          } else {
            return missingOrd;
          }
        };
      }
      return providers;
    }

    @Override
    public DocComparator getDocComparator(LeafReader reader, int maxDoc) throws IOException {
      final SortedDocValues sorted = valuesProvider.get(reader);
      final int missingOrd;
      if (missingValue == SortField.STRING_LAST) {
        missingOrd = Integer.MAX_VALUE;
      } else {
        missingOrd = Integer.MIN_VALUE;
      }

      final int[] ords = new int[maxDoc];
      Arrays.fill(ords, missingOrd);
      int docID;
      while ((docID = sorted.nextDoc()) != NO_MORE_DOCS) {
        ords[docID] = sorted.ordValue();
      }

      return (docID1, docID2) -> reverseMul * Integer.compare(ords[docID1], ords[docID2]);
    }

    @Override
    public String getProviderName() {
      return providerName;
    }
  }

}