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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.search.join;

import org.apache.lucene.index.NumericDocValues;
import org.apache.lucene.index.SortedDocValues;
import org.apache.lucene.index.SortedNumericDocValues;
import org.apache.lucene.index.SortedSetDocValues;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.SortField;
import org.apache.lucene.search.SortedNumericSelector;
import org.apache.lucene.search.SortedSetSelector;
import org.apache.lucene.util.BitSet;
import org.apache.lucene.util.BitSetIterator;
import org.apache.lucene.util.Bits;

/**
 * Select a value from a block of documents.
 *
 * @lucene.internal
 */
public class BlockJoinSelector {

  private BlockJoinSelector() {}

  /**
   * Type of selection to perform. If none of the documents in the block have a value then no value
   * will be selected.
   */
  public enum Type {
    /** Only consider the minimum value from the block when sorting. */
    MIN,
    /** Only consider the maximum value from the block when sorting. */
    MAX;
  }

  /**
   * Return a {@link Bits} instance that returns true if, and only if, any of the children of the
   * given parent document has a value.
   */
  public static Bits wrap(final Bits docsWithValue, BitSet parents, BitSet children) {
    return new Bits() {

      @Override
      public boolean get(int docID) {
        assert parents.get(docID) : "this selector may only be used on parent documents";

        if (docID == 0) {
          // no children
          return false;
        }

        final int firstPotentialChild = parents.prevSetBit(docID - 1) + 1;
        assert firstPotentialChild <= docID;
        if (firstPotentialChild == docID) {
          // no children
          return false;
        }
        for (int child = children.nextSetBit(firstPotentialChild, docID);
            child != DocIdSetIterator.NO_MORE_DOCS;
            child = children.nextSetBit(child + 1, docID)) {
          if (docsWithValue.get(child)) {
            return true;
          }
        }

        return false;
      }

      @Override
      public int length() {
        return docsWithValue.length();
      }
    };
  }

  /**
   * Wraps the provided {@link SortedSetDocValues} in order to only select one value per parent
   * among its {@code children} using the configured {@code selection} type.
   */
  public static SortedDocValues wrap(
      SortedSetDocValues sortedSet, Type selection, BitSet parents, DocIdSetIterator children) {
    SortedDocValues values;
    switch (selection) {
      case MIN:
        values = SortedSetSelector.wrap(sortedSet, SortedSetSelector.Type.MIN);
        break;
      case MAX:
        values = SortedSetSelector.wrap(sortedSet, SortedSetSelector.Type.MAX);
        break;
      default:
        throw new AssertionError();
    }
    return wrap(values, selection, parents, children);
  }

  /**
   * Wraps the provided {@link SortedDocValues} in order to only select one value per parent among
   * its {@code children} using the configured {@code selection} type.
   */
  public static SortedDocValues wrap(
      final SortedDocValues values, Type selection, BitSet parents, DocIdSetIterator children) {
    if (values.docID() != -1) {
      throw new IllegalArgumentException(
          "values iterator was already consumed: values.docID=" + values.docID());
    }
    return ToParentDocValues.wrap(values, selection, parents, children);
  }

  /** creates an iterator for the given bitset */
  protected static BitSetIterator toIter(BitSet children) {
    return new BitSetIterator(children, 0);
  }

  /**
   * Wraps the provided {@link SortedNumericDocValues} in order to only select one value per parent
   * among its {@code children} using the configured {@code selection} type.
   */
  public static NumericDocValues wrap(
      SortedNumericDocValues sortedNumerics,
      Type selection,
      BitSet parents,
      DocIdSetIterator children) {
    NumericDocValues values;
    switch (selection) {
      case MIN:
        values =
            SortedNumericSelector.wrap(
                sortedNumerics, SortedNumericSelector.Type.MIN, SortField.Type.LONG);
        break;
      case MAX:
        values =
            SortedNumericSelector.wrap(
                sortedNumerics, SortedNumericSelector.Type.MAX, SortField.Type.LONG);
        break;
      default:
        throw new AssertionError();
    }
    return wrap(values, selection, parents, children);
  }

  /**
   * Wraps the provided {@link NumericDocValues}, iterating over only child documents, in order to
   * only select one value per parent among its {@code children} using the configured {@code
   * selection} type.
   */
  public static NumericDocValues wrap(
      final NumericDocValues values, Type selection, BitSet parents, DocIdSetIterator children) {
    if (values.docID() != -1) {
      throw new IllegalArgumentException(
          "values iterator was already consumed: values.docID=" + values.docID());
    }
    return ToParentDocValues.wrap(values, selection, parents, children);
  }
}