lucene/facet/src/java/org/apache/lucene/facet/sortedset/SortedSetDocValuesReaderState.java

/*
 * 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.facet.sortedset;

import java.io.IOException;
import java.util.Map;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.SortedSetDocValues;
import org.apache.lucene.util.Accountable;

/** Wraps a {@link IndexReader} and resolves ords
 *  using existing {@link SortedSetDocValues} APIs without a
 *  separate taxonomy index.  This only supports flat facets
 *  (dimension + label), and it makes faceting a bit
 *  slower, adds some cost at reopen time, but avoids
 *  managing the separate taxonomy index.  It also requires
 *  less RAM than the taxonomy index, as it manages the flat
 *  (2-level) hierarchy more efficiently.  In addition, the
 *  tie-break during faceting is now meaningful (in label
 *  sorted order).
 *
 *  <p><b>NOTE</b>: creating an instance of this class is
 *  somewhat costly, as it computes per-segment ordinal maps,
 *  so you should create it once and re-use that one instance
 *  for a given {@link IndexReader}. */

public abstract class SortedSetDocValuesReaderState implements Accountable {

  /** Holds start/end range of ords, which maps to one
   *  dimension (someday we may generalize it to map to
   *  hierarchies within one dimension). */
  public static final class OrdRange {
    /** Start of range, inclusive: */
    public final int start;
    /** End of range, inclusive: */
    public final int end;

    /** Start and end are inclusive. */
    public OrdRange(int start, int end) {
      this.start = start;
      this.end = end;
    }
  }

  /** Sole constructor. */
  protected SortedSetDocValuesReaderState() {
  }
  
  /** Return top-level doc values. */
  public abstract SortedSetDocValues getDocValues() throws IOException;
  
  /** Indexed field we are reading. */
  public abstract String getField();
  
  /** Returns the {@link OrdRange} for this dimension. */
  public abstract OrdRange getOrdRange(String dim);
  
  /** Returns mapping from prefix to {@link OrdRange}. */
  public abstract Map<String,OrdRange> getPrefixToOrdRange();

  /** Returns top-level index reader. */
  public abstract IndexReader getReader();
  
  /** Number of unique labels. */
  public abstract int getSize();
}