org.eclipse.jface.text/src/org/eclipse/jface/text/rules/BufferedRuleBasedScanner.java

/**********************************************************************
Copyright (c) 2000, 2002 IBM Corp. 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 implementation
**********************************************************************/

package org.eclipse.jface.text.rules;

import org.eclipse.jface.text.Assert;
import org.eclipse.jface.text.BadLocationException;
import org.eclipse.jface.text.IDocument;

/**
 * A buffered rule based scanner. The buffer always contains a section 
 * of a fixed size of the document to be scanned.
 */
public class BufferedRuleBasedScanner extends RuleBasedScanner {
	
	private final static int DEFAULT_BUFFER_SIZE= 500;
	
	private int fBufferSize= DEFAULT_BUFFER_SIZE;
	private char[] fBuffer= new char[DEFAULT_BUFFER_SIZE];
	
	private int fStart;
	private int fEnd;
	private int fDocumentLength;
	
	
	/**
	 * Creates a new buffered rule based scanner which does 
	 * not have any rule and a default buffer size of 500 characters.
	 */
	protected BufferedRuleBasedScanner() {
		super();
	}
	
	/**
	 * Creates a new buffered rule based scanner which does 
	 * not have any rule. The buffer size is set to the given
	 * number of characters.
	 *
	 * @param size the buffer size
	 */
	public BufferedRuleBasedScanner(int size) {
		super();
		setBufferSize(size);
	}
	
	/**
	 * Sets the buffer to the given number of characters.
	 *
	 * @param size the buffer size
	 */
	protected void setBufferSize(int size) {
		Assert.isTrue(size > 0);
		fBufferSize= size;
		fBuffer= new char[size];
	}
	
	/**
	 * Shifts the buffer so that the buffer starts at the 
	 * given document offset.
	 *
	 * @param offset the document offset at which the buffer starts
	 */
	private void shiftBuffer(int offset) {
				
		fStart= offset;
		fEnd= fStart + fBufferSize;
		if (fEnd > fDocumentLength)
			fEnd= fDocumentLength;
			
		try {
			
			String content= fDocument.get(fStart, fEnd - fStart);
			content.getChars(0, fEnd - fStart, fBuffer, 0);
			
		} catch (BadLocationException x) {
		}
	}
	
	/*
	 * @see RuleBasedScanner#setRange
	 */
	public void setRange(IDocument document, int offset, int length) {
		
		super.setRange(document, offset, length);
		
		fDocumentLength= document.getLength();
		shiftBuffer(offset);
	}
	
	/*
	 * @see RuleBasedScanner#read
	 */
	public int read() {
		
		if (fOffset >= fRangeEnd) {
			++ fOffset;
			return EOF;
		}
				
		if (fOffset == fEnd)
			shiftBuffer(fEnd);
		else if (fOffset < fStart || fEnd < fOffset)
			shiftBuffer(fOffset);
			
		return fBuffer[fOffset++ - fStart];			
	}
	
	/*
	 * @see RuleBasedScanner#unread
	 */
	public void unread() {
		
		if (fOffset == fStart)
			shiftBuffer(Math.max(0, fStart - (fBufferSize / 2)));
			
		-- fOffset;
	}
}