package org.apache.lucene.search.spell;

/**
 * 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 org.apache.lucene.index.IndexReader;

import java.util.Iterator;

import org.apache.lucene.index.TermEnum;
import org.apache.lucene.index.Term;

import java.io.*;

/**
 * Lucene Dictionary: terms taken from the given field
 * of a Lucene index.
 *
 * 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
 *
 * @author Nicolas Maisonneuve
 * @author Christian Mallwitz
 */
public class LuceneDictionary implements Dictionary {
  private IndexReader reader;
  private String field;

  public LuceneDictionary(IndexReader reader, String field) {
    this.reader = reader;
    this.field = field.intern();
  }

  public final Iterator getWordsIterator() {
    return new LuceneIterator();
  }


  final class LuceneIterator implements Iterator {
    private TermEnum termEnum;
    private Term actualTerm;
    private boolean hasNextCalled;

    LuceneIterator() {
      try {
        termEnum = reader.terms(new Term(field, ""));
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }

    public Object next() {
      if (!hasNextCalled) {
        hasNext();
      }
      hasNextCalled = false;

      try {
        termEnum.next();
      } catch (IOException e) {
        throw new RuntimeException(e);
      }

      return (actualTerm != null) ? actualTerm.text() : null;
    }

    public boolean hasNext() {
      if (hasNextCalled) {
        return actualTerm != null;
      }
      hasNextCalled = true;

      actualTerm = termEnum.term();

      // 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) {
        actualTerm = null;
        return false;
      }

      return true;
    }

    public void remove() {
      throw new UnsupportedOperationException();
    }
  }
}