/*
 * 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.taxonomy;

import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.util.IntsRef;

import java.io.IOException;

import static org.apache.lucene.facet.taxonomy.TaxonomyReader.INVALID_ORDINAL;
import static org.apache.lucene.facet.taxonomy.TaxonomyReader.ROOT_ORDINAL;

Utility class to easily retrieve previously indexed facet labels, allowing you to skip also adding stored fields for these values,
reducing your index size.
@lucene.experimental
/**
 * Utility class to easily retrieve previously indexed facet labels, allowing you to skip also adding stored fields for these values,
 * reducing your index size.
 *
 * @lucene.experimental
 **/
public class TaxonomyFacetLabels {

  
Index field name provided to the constructor
/**
   * Index field name provided to the constructor
   */
  private final String indexFieldName;

  
TaxonomyReader provided to the constructor /**
   * {@code TaxonomyReader} provided to the constructor
   */
  private final TaxonomyReader taxoReader;


  
OrdinalsReader to decode ordinals previously indexed into the BinaryDocValues facet field /**
   * {@code OrdinalsReader} to decode ordinals previously indexed into the {@code BinaryDocValues} facet field
   */
  private final OrdinalsReader ordsReader;

  
Sole constructor. Do not close the provided TaxonomyReader while still using this instance! /**
   * Sole constructor.  Do not close the provided {@link TaxonomyReader} while still using this instance!
   */
  public TaxonomyFacetLabels(TaxonomyReader taxoReader, String indexFieldName) throws IOException {
    this.taxoReader = taxoReader;
    this.indexFieldName = indexFieldName;
    this.ordsReader = new DocValuesOrdinalsReader(indexFieldName);
  }

  
Create and return an instance of FacetLabelReader to retrieve facet labels for multiple documents and (optionally) for a specific dimension. You must create this per-segment, and then step through all hits, in order, for that segment. 
NOTE: This class is not thread-safe, so you must use a new instance of this
class for each thread.
Params:
readerContext – LeafReaderContext used to access the BinaryDocValues facet field
Throws:
IOException – when a low-level IO issue occurs
Returns:
an instance of FacetLabelReader/**
   * Create and return an instance of {@link FacetLabelReader} to retrieve facet labels for
   * multiple documents and (optionally) for a specific dimension.  You must create this per-segment,
   * and then step through all hits, in order, for that segment.
   *
   * <p><b>NOTE</b>: This class is not thread-safe, so you must use a new instance of this
   * class for each thread.</p>
   *
   * @param readerContext LeafReaderContext used to access the {@code BinaryDocValues} facet field
   * @return an instance of {@link FacetLabelReader}
   * @throws IOException when a low-level IO issue occurs
   */
  public FacetLabelReader getFacetLabelReader(LeafReaderContext readerContext) throws IOException {
    return new FacetLabelReader(ordsReader, readerContext);
  }

  
Utility class to retrieve facet labels for multiple documents.
@lucene.experimental
/**
   * Utility class to retrieve facet labels for multiple documents.
   *
   * @lucene.experimental
   */
  public class FacetLabelReader {
    private final OrdinalsReader.OrdinalsSegmentReader ordinalsSegmentReader;
    private final IntsRef decodedOrds = new IntsRef();
    private int currentDocId = -1;
    private int currentPos = -1;

    // Lazily set when nextFacetLabel(int docId, String facetDimension) is first called
    private int[] parents;

    
Sole constructor.
/**
     * Sole constructor.
     */
    public FacetLabelReader(OrdinalsReader ordsReader, LeafReaderContext readerContext) throws IOException {
      ordinalsSegmentReader = ordsReader.getReader(readerContext);
    }

    
Retrieves the next FacetLabel for the specified docId, or null if there are no more. This method has state: if the provided docId is the same as the previous invocation, it returns the next FacetLabel for that document. Otherwise, it advances to the new docId and provides the first FacetLabel for that document, or null if that document has no indexed facets. Each new docId must be in strictly monotonic (increasing) order. 
NOTE: The returned FacetLabels may not be in the same order in which they were indexed
Params:
docId – input docId provided in monotonic (non-decreasing) order
Throws:
IOException – when a low-level IO issue occurs
IllegalArgumentException – if docId provided is less than docId supplied in an earlier invocation
Returns:
the first or next FacetLabel, or null if there are no more/**
     * Retrieves the next {@link FacetLabel} for the specified {@code docId}, or {@code null} if there are no more.
     * This method has state: if the provided {@code docId} is the same as the previous invocation, it returns the
     * next {@link FacetLabel} for that document.  Otherwise, it advances to the new {@code docId} and provides the
     * first {@link FacetLabel} for that document, or {@code null} if that document has no indexed facets.  Each
     * new {@code docId} must be in strictly monotonic (increasing) order.
     *
     * <p><b>NOTE</b>: The returned FacetLabels may not be in the same order in which they were indexed</p>
     *
     * @param docId input docId provided in monotonic (non-decreasing) order
     * @return the first or next {@link FacetLabel}, or {@code null} if there are no more
     * @throws IOException when a low-level IO issue occurs
     * @throws IllegalArgumentException if docId provided is less than docId supplied in an earlier invocation
     */
    public FacetLabel nextFacetLabel(int docId) throws IOException {
      if (currentDocId != docId) {
        if (docId < currentDocId) {
          throw new IllegalArgumentException("docs out of order: previous docId=" + currentDocId
              + " current docId=" + docId);
        }
        ordinalsSegmentReader.get(docId, decodedOrds);
        currentDocId = docId;
        currentPos = decodedOrds.offset;
      }

      int endPos = decodedOrds.offset + decodedOrds.length;
      assert currentPos <= endPos;

      if (currentPos == endPos) {
        // no more FacetLabels
        return null;
      }

      int ord = decodedOrds.ints[currentPos++];
      return taxoReader.getPath(ord);
    }

    private boolean isDescendant(int ord, int ancestorOrd) {
      while (ord != INVALID_ORDINAL && ord != ROOT_ORDINAL) {
        if (parents[ord] == ancestorOrd) {
          return true;
        }
        ord = parents[ord];
      }
      return false;
    }

    
Retrieves the next FacetLabel for the specified docId under the requested facetDimension, or null if there are no more. This method has state: if the provided docId is the same as the previous invocation, it returns the next FacetLabel for that document. Otherwise, it advances to the new docId and provides the first FacetLabel for that document, or null if that document has no indexed facets. Each new docId must be in strictly monotonic (increasing) order. 
NOTE: This method loads the int[] parents array from the taxonomy index. The returned FacetLabels may not be in the same order in which they were indexed.
Params:
docId – input docId provided in non-decreasing order
Throws:
IOException – if TaxonomyReader has problems getting path for an ordinal
IllegalArgumentException – if docId provided is less than docId supplied in an earlier invocation
IllegalArgumentException – if facetDimension is null
Returns:
the first or next FacetLabel, or null if there are no more/**
     * Retrieves the next {@link FacetLabel} for the specified {@code docId} under the requested {@code facetDimension},
     * or {@code null} if there are no more. This method has state: if the provided {@code docId} is the same as the
     * previous invocation, it returns the next {@link FacetLabel} for that document.  Otherwise, it advances to
     * the new {@code docId} and provides the first {@link FacetLabel} for that document, or {@code null} if that document
     * has no indexed facets.  Each new {@code docId} must be in strictly monotonic (increasing) order.
     *
     * <p><b>NOTE</b>: This method loads the {@code int[] parents} array from the taxonomy index.
     * The returned FacetLabels may not be in the same order in which they were indexed.</p>
     *
     * @param docId input docId provided in non-decreasing order
     * @return the first or next {@link FacetLabel}, or {@code null} if there are no more
     * @throws IOException if {@link TaxonomyReader} has problems getting path for an ordinal
     * @throws IllegalArgumentException if docId provided is less than docId supplied in an earlier invocation
     * @throws IllegalArgumentException if facetDimension is null
     */
    public FacetLabel nextFacetLabel(int docId, String facetDimension) throws IOException {
      if (facetDimension == null) {
        throw new IllegalArgumentException("Input facet dimension cannot be null");
      }
      final int parentOrd = taxoReader.getOrdinal(new FacetLabel(facetDimension));
      if (parentOrd == INVALID_ORDINAL) {
        throw new IllegalArgumentException("Category ordinal not found for facet dimension: " + facetDimension);
      }

      if (currentDocId != docId) {
        if (docId < currentDocId) {
          throw new IllegalArgumentException("docs out of order: previous docId=" + currentDocId
              + " current docId=" + docId);
        }
        ordinalsSegmentReader.get(docId, decodedOrds);
        currentPos = decodedOrds.offset;
        currentDocId = docId;
      }

      if (parents == null) {
        parents = taxoReader.getParallelTaxonomyArrays().parents();
      }

      int endPos = decodedOrds.offset + decodedOrds.length;
      assert currentPos <= endPos;

      for (; currentPos < endPos; ) {
        int ord = decodedOrds.ints[currentPos++];
        if (isDescendant(ord, parentOrd) == true) {
          return taxoReader.getPath(ord);
        }
      }
      return null;
    }
  }
}