/*******************************************************************************
 * Copyright (c) 2000, 2003 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/

package org.eclipse.jface.text.rules;

import org.eclipse.jface.text.Assert;


/**
 * An implementation of <code>IRule</code> capable of detecting a numerical value.
 */
public class NumberRule implements IRule {
	
	/** Internal setting for the uninitialized column constraint */
	protected static final int UNDEFINED= -1;
	/** The token to be returned when this rule is successful */
	protected IToken fToken;
	/** The column constraint */
	protected int fColumn= UNDEFINED;

	/**
	 * Creates a rule which will return the specified
	 * token when a numerical sequence is detected.
	 *
	 * @param token the token to be returned
	 */
	public NumberRule(IToken token) {
		Assert.isNotNull(token);
		fToken= token;
	}

	/**
	 * Sets a column constraint for this rule. If set, the rule's token
	 * will only be returned if the pattern is detected starting at the 
	 * specified column. If the column is smaller then 0, the column
	 * constraint is considered removed.
	 *
	 * @param column the column in which the pattern starts
	 */
	public void setColumnConstraint(int column) {
		if (column < 0)
			column= UNDEFINED;
		fColumn= column;
	}

	/*
	 * @see IRule#evaluate(ICharacterScanner)
	 */
	public IToken evaluate(ICharacterScanner scanner) {
		int c= scanner.read();
		if (Character.isDigit((char)c)) {
			if (fColumn == UNDEFINED || (fColumn == scanner.getColumn() - 1)) {
				do {
					c= scanner.read();
				} while (Character.isDigit((char) c));
				scanner.unread();
				return fToken;
			}
		}
		
		scanner.unread();
		return Token.UNDEFINED;
	}
}