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The Adobe Experience Manager SDK
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package org.apache.lucene.search.suggest;

/*
 * 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.
 */
import java.io.IOException;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Set;

import org.apache.lucene.document.Document;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexableField;
import org.apache.lucene.index.MultiDocValues;
import org.apache.lucene.index.MultiFields;
import org.apache.lucene.index.NumericDocValues;
import org.apache.lucene.search.spell.Dictionary;
import org.apache.lucene.util.Bits;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefIterator;

/**
 * 
 * Dictionary with terms, weights and optionally payload information 
 * taken from stored/indexed fields in a Lucene index.
 * 
 * NOTE: 
 *  
 *    
 *      The term and (optionally) payload fields have to be
 *      stored
 *    
 *    
 *      The weight field can be stored or can be a {@link NumericDocValues}.
 *      If the weight field is not defined, the value of the weight is 0
 *    
 *    
 *      if any of the term or (optionally) payload fields supplied
 *      do not have a value for a document, then the document is 
 *      skipped by the dictionary
 *    
 *  
 */
public class DocumentDictionary implements Dictionary {
  
  /** {@link IndexReader} to load documents from */
  protected final IndexReader reader;

  /** Field to read payload from */
  protected final String payloadField;
  private final String field;
  private final String weightField;
  
  /**
   * Creates a new dictionary with the contents of the fields named field
   * for the terms and weightField for the weights that will be used for
   * the corresponding terms.
   */
  public DocumentDictionary(IndexReader reader, String field, String weightField) {
    this(reader, field, weightField, null);
  }
  
  /**
   * Creates a new dictionary with the contents of the fields named field
   * for the terms, weightField for the weights that will be used for the 
   * the corresponding terms and payloadField for the corresponding payloads
   * for the entry.
   */
  public DocumentDictionary(IndexReader reader, String field, String weightField, String payloadField) {
    this.reader = reader;
    this.field = field;
    this.weightField = weightField;
    this.payloadField = payloadField;
  }
  
  @Override
  public InputIterator getEntryIterator() throws IOException {
    return new DocumentInputIterator(payloadField!=null);
  }

  /** Implements {@link InputIterator} from stored fields. */
  protected class DocumentInputIterator implements InputIterator {

    private final int docCount;
    private final Set relevantFields;
    private final boolean hasPayloads;
    private final Bits liveDocs;
    private int currentDocId = -1;
    private long currentWeight;
    private BytesRef currentPayload;
    private final NumericDocValues weightValues;
    
    
    /**
     * Creates an iterator over term, weight and payload fields from the lucene
     * index. setting withPayload to false, implies an iterator
     * over only term and weight.
     */
    public DocumentInputIterator(boolean hasPayloads) throws IOException {
      this.hasPayloads = hasPayloads;
      docCount = reader.maxDoc() - 1;
      weightValues = (weightField != null) ? MultiDocValues.getNumericValues(reader, weightField) : null;
      liveDocs = (reader.leaves().size() > 0) ? MultiFields.getLiveDocs(reader) : null;
      relevantFields = getRelevantFields(new String [] {field, weightField, payloadField});
    }

    @Override
    public long weight() {
      return currentWeight;
    }

    @Override
    public Comparator getComparator() {
      return null;
    }

    @Override
    public BytesRef next() throws IOException {
      while (currentDocId < docCount) {
        currentDocId++;
        if (liveDocs != null && !liveDocs.get(currentDocId)) { 
          continue;
        }

        Document doc = reader.document(currentDocId, relevantFields);
        
        BytesRef tempPayload = null;
        BytesRef tempTerm = null;
        
        if (hasPayloads) {
          IndexableField payload = doc.getField(payloadField);
          if (payload == null || (payload.binaryValue() == null && payload.stringValue() == null)) {
            continue;
          }
          tempPayload = (payload.binaryValue() != null) ? payload.binaryValue() : new BytesRef(payload.stringValue());
        }
        
        IndexableField fieldVal = doc.getField(field);
        if (fieldVal == null || (fieldVal.binaryValue() == null && fieldVal.stringValue() == null)) {
          continue;
        }
        tempTerm = (fieldVal.stringValue() != null) ? new BytesRef(fieldVal.stringValue()) : fieldVal.binaryValue();
        
        currentPayload = tempPayload;
        currentWeight = getWeight(doc, currentDocId);
        
        return tempTerm;
      }
      return null;
    }

    @Override
    public BytesRef payload() {
      return currentPayload;
    }

    @Override
    public boolean hasPayloads() {
      return hasPayloads;
    }
    
    /** 
     * Returns the value of the weightField for the current document.
     * Retrieves the value for the weightField if its stored (using doc)
     * or if its indexed as {@link NumericDocValues} (using docId) for the document.
     * If no value is found, then the weight is 0.
     */
    protected long getWeight(Document doc, int docId) {
      IndexableField weight = doc.getField(weightField);
      if (weight != null) { // found weight as stored
        return (weight.numericValue() != null) ? weight.numericValue().longValue() : 0;
      } else if (weightValues != null) {  // found weight as NumericDocValue
        return weightValues.get(docId);
      } else { // fall back
        return 0;
      }
    }
    
    private Set getRelevantFields(String... fields) {
      Set relevantFields = new HashSet();
      for (String relevantField : fields) {
        if (relevantField != null) {
          relevantFields.add(relevantField);
        }
      }
      return relevantFields;
    }
  }
}