content: /**
   * 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.spell;
  
  import java.io.IOException;
  import java.util.Iterator;
  
  import org.apache.lucene.index.IndexReader;
  import org.apache.lucene.index.Term;
  import org.apache.lucene.index.TermEnum;
  import org.apache.lucene.search.spell.Dictionary;
  import org.apache.lucene.util.StringHelper;
  
  /**
   * HighFrequencyDictionary: terms taken from the given field
   * of a Lucene index, which appear in a number of documents
   * above a given threshold.
   *
   * When using IndexReader.terms(Term) the code must not call next() on TermEnum
   * as the first call to TermEnum, see: http://issues.apache.org/jira/browse/LUCENE-6
   *
   * Threshold is a value in [0..1] representing the minimum
   * number of documents (of the total) where a term should appear.
   * 
   * Based on LuceneDictionary.
   */
  public class HighFrequencyDictionary implements Dictionary {
    private IndexReader reader;
    private String field;
    private float thresh;
  
    public HighFrequencyDictionary(IndexReader reader, String field, float thresh) {
      this.reader = reader;
      this.field = StringHelper.intern(field);
      this.thresh = thresh;
    }
  
    public final Iterator<String> getWordsIterator() {
      return new HighFrequencyIterator();
    }
  
    final class HighFrequencyIterator implements TermFreqIterator {
      private TermEnum termEnum;
      private Term actualTerm;
      private int actualFreq;
      private boolean hasNextCalled;
      private int minNumDocs;
  
      HighFrequencyIterator() {
        try {
          termEnum = reader.terms(new Term(field, ""));
          minNumDocs = (int)(thresh * (float)reader.numDocs());
        } catch (IOException e) {
          throw new RuntimeException(e);
        }
      }
  
      private boolean isFrequent(Term term) {
        try {
          return reader.docFreq(term) >= minNumDocs;
        } catch (IOException e) {
          throw new RuntimeException(e);
        }
      }
  
      public String next() {
        if (!hasNextCalled) {
          hasNext();
        }
        hasNextCalled = false;
  
        try {
          termEnum.next();
        } catch (IOException e) {
          throw new RuntimeException(e);
        }
  
        return (actualTerm != null) ? actualTerm.text() : null;
      }
  
      public float freq() {
        return actualFreq;
      }
  
  
      public boolean hasNext() {
        if (hasNextCalled) {
          return actualTerm != null;
        }
        hasNextCalled = true;
  
        do {
          actualTerm = termEnum.term();
          actualFreq = termEnum.docFreq();
  
          // if there are no words return false
          if (actualTerm == null) {
            return false;
          }
  
          String currentField = actualTerm.field();
  
          // if the next word doesn't have the same field return false
          if (currentField != field) {   // intern'd comparison
            actualTerm = null;
            return false;
          }
  
          // got a valid term, does it pass the threshold?
          if (isFrequent(actualTerm)) {
            return true;
          }
  
          // term not up to threshold
          try {
            termEnum.next();
          } catch (IOException e) {
            throw new RuntimeException(e);
          }
  
        } while (true);
      }
  
      public void remove() {
        throw new UnsupportedOperationException();
      }
    }
  }
  