package org.apache.lucene.misc;

/**
  * Copyright 2004 The Apache Software Foundation
  *
  * Licensed 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 org.apache.lucene.index.Term;
import org.apache.lucene.index.TermEnum;
import org.apache.lucene.util.PriorityQueue;

/**
 * <code>HighFreqTerms</code> class extracts terms and their frequencies out
 * of an existing Lucene index.
 *
 * @version $Id: HighFreqTerms.java 376393 2006-02-09 19:17:14Z otis $
 */
public class HighFreqTerms {
  
  // The top numTerms will be displayed
  public static final int numTerms = 100;

  public static void main(String[] args) throws Exception {
    IndexReader reader = null;
    String field = null;
    if (args.length == 1) {
      reader = IndexReader.open(args[0]);
    } else if (args.length == 2) {
      reader = IndexReader.open(args[0]);
      field = args[1];
    } else {
      usage();
      System.exit(1);
    }

    TermInfoQueue tiq = new TermInfoQueue(numTerms);
    TermEnum terms = reader.terms();

    if (field != null) { 
      while (terms.next()) {
        if (terms.term().field().equals(field)) {
          tiq.insert(new TermInfo(terms.term(), terms.docFreq()));
        }
      }
    }
    else {
      while (terms.next()) {
        tiq.insert(new TermInfo(terms.term(), terms.docFreq()));
      }
    }
    while (tiq.size() != 0) {
      TermInfo termInfo = (TermInfo) tiq.pop();
      System.out.println(termInfo.term + " " + termInfo.docFreq);
    }

    reader.close();
  }

  private static void usage() {
    System.out.println(
         "\n\n"
         + "java org.apache.lucene.misc.HighFreqTerms <index dir> [field]\n\n");
  }
}

final class TermInfo {
  TermInfo(Term t, int df) {
    term = t;
    docFreq = df;
  }
  int docFreq;
  Term term;
}

final class TermInfoQueue extends PriorityQueue {
  TermInfoQueue(int size) {
    initialize(size);
  }
  protected final boolean lessThan(Object a, Object b) {
    TermInfo termInfoA = (TermInfo) a;
    TermInfo termInfoB = (TermInfo) b;
    return termInfoA.docFreq < termInfoB.docFreq;
  }
}