/*
 *  gnu/regexp/REMatchEnumeration.java
 *  Copyright (C) 1998-2001 Wes Biggs
 *
 *  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 program; if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
package gnu.regexp;
import java.io.Serializable;
import java.util.Enumeration;
import java.util.NoSuchElementException;

/**
 * An REMatchEnumeration enumerates regular expression matches over a
 * given input text.  You obtain a reference to an enumeration using
 * the <code>getMatchEnumeration()</code> methods on an instance of
 * RE. 
 *
 * <P>
 *
 * REMatchEnumeration does lazy computation; that is, it will not
 * search for a match until it needs to.  If you'd rather just get all
 * the matches at once in a big array, use the
 * <code>getAllMatches()</code> methods on RE.  However, using an
 * enumeration can help speed performance when the entire text does
 * not need to be searched immediately.
 *
 * <P>
 * 
 * The enumerated type is especially useful when searching on a Reader
 * or InputStream, because the InputStream read position cannot be
 * guaranteed after calling <code>getMatch()</code> (see the
 * description of that method for an explanation of why).  Enumeration
 * also saves a lot of overhead required when calling
 * <code>getMatch()</code> multiple times.
 * 
 * @author <A HREF="mailto:wes@cacas.org">Wes Biggs</A> 
 */
public class REMatchEnumeration implements Enumeration, Serializable {
  private static final int YES = 1;
  private static final int MAYBE = 0;
  private static final int NO = -1;
  
  private int more;
  private REMatch match;
  private RE expr;
  private CharIndexed input;
  private int eflags;
    private int index;

  // Package scope constructor is used by RE.getMatchEnumeration()
  REMatchEnumeration(RE expr, CharIndexed input, int index, int eflags) {
    more = MAYBE;
    this.expr = expr;
    this.input = input;
    this.index = index;
    this.eflags = eflags;
  }

  /** Returns true if there are more matches in the input text. */
  public boolean hasMoreElements() {
    return hasMoreMatches(null);
  }

  /** Returns true if there are more matches in the input text. */
  public boolean hasMoreMatches() {
    return hasMoreMatches(null);
  }

  /** Returns true if there are more matches in the input text.
   * Saves the text leading up to the match (or to the end of the input)
   * in the specified buffer.
   */
  public boolean hasMoreMatches(StringBuffer buffer) {
    if (more == MAYBE) {
	match = expr.getMatchImpl(input,index,eflags,buffer);
	if (match != null) {
	    input.move((match.end[0] > 0) ? match.end[0] : 1);
	    
	    index = (match.end[0] > 0) ? match.end[0] + match.offset : index + 1;
	    more = YES;
	} else more = NO;
    }
    return (more == YES);
  }

  /** Returns the next match in the input text. */
  public Object nextElement() throws NoSuchElementException {
    return nextMatch();
  }

  /** 
   * Returns the next match in the input text. This method is provided
   * for convenience to avoid having to explicitly cast the return value
   * to class REMatch.
   */
  public REMatch nextMatch() throws NoSuchElementException {
    if (hasMoreElements()) {
	more = (input.isValid()) ? MAYBE : NO;
	return match;
    }
    throw new NoSuchElementException();
  }
}