/*

         StatCvs - CVS statistics generation 

         Copyright (C) 2002  Lukasz Pekacki <lukasz@pekacki.de>

         http://statcvs.sf.net/

         This library is free software; you can redistribute it and/or

         modify it under the terms of the GNU Lesser General Public

         License as published by the Free Software Foundation; either

         version 2.1 of the License, or (at your option) any later version.

         This library is distributed in the hope that it will be useful,

         but WITHOUT ANY WARRANTY; without even the implied warranty of

         MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

         Lesser General Public License for more details.

         You should have received a copy of the GNU Lesser General Public

         License along with this library; if not, write to the Free Software

         Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

         $RCSfile: LookaheadReader.java,v $

         $Date: 2008/04/02 11:22:15 $

 */

 package net.sf.statcvs.util;

 import java.io.BufferedReader;

 import java.io.IOException;

 import java.io.Reader;

 import java.util.NoSuchElementException;

 /**

  * <p>Wraps a {@link java.io.Reader} for line-by-line access.

  * This works like {@link java.util.Iterator}: {@link #hasNextLine}

  * returns true if another line can be read; {@link #nextLine} reads

  * the next line and returns it. Additionally, {@link #getCurrentLine}

  * can be used to access multiple times the line returned by

  * <tt>nextLine()</tt>.</p>

  * 

  * <p>At construction time, <tt>getCurrentLine()</tt> is undefined.

  * <tt>nextLine()</tt> must be called once to read the first line.</p>

  * 

  * @author Richard Cyganiak (richard@cyganiak.de)

  * @version $Id: LookaheadReader.java,v 1.4 2008/04/02 11:22:15 benoitx Exp $

  */

 public class LookaheadReader {

     private final BufferedReader reader;

     private String currentLine = null;

     private String nextLine = null;

     private boolean afterEnd = false;

     private int lineNumber = 0;

     /**

      * Creates a LookaheadReader from a source reader.

      * @param reader a reader whose contents will be returned by the

      *                         LookaheadReader

      */

     public LookaheadReader(final Reader reader) {

         this.reader = new BufferedReader(reader);

     }

     /**

      * Returns the current line without reading a line from the source

      * reader. Will throw an exception if {@link #nextLine} was not

      * called before.

      * @return The line returned by the previous call to {@link #nextLine()}

      * @throws NoSuchElementException if {@link #nextLine} was not yet called

      */

     public String getCurrentLine() {

         if (this.currentLine == null) {

             throw new NoSuchElementException("Call to getCurrentLine() before nextLine() was called");

         }

         return this.currentLine;

     }

     /**

      * Reads and returns a line from the source reader. The result of

      * this call will be the new current line. Will throw an exception

      * if trying to read from after the end of the source reader.

      * @return The next line of the source reader

      * @throws IOException on error while reading the source reader

      * @throws NoSuchElementException if {@link #hasNextLine} is false 

      */

     public String nextLine() throws IOException {

         if (!hasNextLine()) {

             throw new NoSuchElementException("Call to nextLine() when hasNextLine() is false");

         }

         this.currentLine = this.nextLine;

         this.nextLine = null;

         this.lineNumber++;

         return this.currentLine;

     }

     /**

      * Checks if more lines are available for reading.

      * @return <tt>true</tt> if at least one more line can be read

      * @throws IOException on error while reading the source reader

      */

     public boolean hasNextLine() throws IOException {

         if (this.afterEnd) {

             return false;

         }

         if (this.nextLine != null) {

             return true;

         }

         this.nextLine = this.reader.readLine();

         if (this.nextLine != null) {

             return true;

         }

         this.afterEnd = true;

         return false;

     }

     /**

      * Returns the number of the line that would be returned by

      * {@link #getCurrentLine}, or 0 before the first

      * call to {@link #nextLine}. The first line has line number 1.

      * @return the current line number

      */

     public int getLineNumber() {

         return this.lineNumber;

     }

 }