/*******************************************************************************
 * Copyright (c) 2000, 2004 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 net.sourceforge.phpdt.internal.ui.text;

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

/**
 * A buffered document scanner. The buffer always contains a section of a fixed
 * size of the document to be scanned.
 */

public final class BufferedDocumentScanner implements ICharacterScanner {

	/** The document being scanned. */
	private IDocument fDocument;

	/** The offset of the document range to scan. */
	private int fRangeOffset;

	/** The length of the document range to scan. */
	private int fRangeLength;

	/** The delimiters of the document. */
	private char[][] fDelimiters;

	/** The buffer. */
	private final char[] fBuffer;

	/** The offset of the buffer within the document. */
	private int fBufferOffset;

	/** The valid length of the buffer for access. */
	private int fBufferLength;

	/** The offset of the scanner within the buffer. */
	private int fOffset;

	/**
	 * Creates a new buffered document scanner. The buffer size is set to the
	 * given number of characters.
	 * 
	 * @param size
	 *            the buffer size
	 */
	public BufferedDocumentScanner(int size) {
		Assert.isTrue(size >= 1);
		fBuffer = new char[size];
	}

	/**
	 * Fills the buffer with the contens of the document starting at the given
	 * offset.
	 * 
	 * @param offset
	 *            the document offset at which the buffer starts
	 */
	private final void updateBuffer(int offset) {

		fBufferOffset = offset;

		if (fBufferOffset + fBuffer.length > fRangeOffset + fRangeLength)
			fBufferLength = fRangeLength - (fBufferOffset - fRangeOffset);
		else
			fBufferLength = fBuffer.length;

		try {
			final String content = fDocument.get(fBufferOffset, fBufferLength);
			if (content != null) {
				content.getChars(0, fBufferLength, fBuffer, 0);
			}
		} catch (BadLocationException e) {
		}
	}

	/**
	 * Configures the scanner by providing access to the document range over
	 * which to scan.
	 * 
	 * @param document
	 *            the document to scan
	 * @param offset
	 *            the offset of the document range to scan
	 * @param length
	 *            the length of the document range to scan
	 */
	public final void setRange(IDocument document, int offset, int length) {

		fDocument = document;
		fRangeOffset = offset;
		fRangeLength = length;

		String[] delimiters = document.getLegalLineDelimiters();
		fDelimiters = new char[delimiters.length][];
		for (int i = 0; i < delimiters.length; i++)
			fDelimiters[i] = delimiters[i].toCharArray();

		updateBuffer(offset);
		fOffset = 0;
	}

	/*
	 * @see ICharacterScanner#read()
	 */
	public final int read() {

		if (fOffset == fBufferLength) {
			if (fBufferOffset + fBufferLength == fDocument.getLength())
				return EOF;
			else {
				updateBuffer(fBufferOffset + fBufferLength);
				fOffset = 0;
			}
		}
		try {
			return fBuffer[fOffset++];
		} catch (ArrayIndexOutOfBoundsException e) {
			System.out.println("Offset:" + fOffset);
			System.out.println("Buffer:" + fBuffer.toString());
			throw e;
		}
	}

	/*
	 * @see ICharacterScanner#unread
	 */
	public final void unread() {

		if (fOffset == 0) {
			if (fBufferOffset == fRangeOffset) {
				// error: BOF
			} else {
				updateBuffer(fBufferOffset - fBuffer.length);
				fOffset = fBuffer.length - 1;
			}
		} else {
			--fOffset;
		}
	}

	/*
	 * @see ICharacterScanner#getColumn()
	 */
	public final int getColumn() {

		try {
			final int offset = fBufferOffset + fOffset;
			final int line = fDocument.getLineOfOffset(offset);
			final int start = fDocument.getLineOffset(line);
			return offset - start;
		} catch (BadLocationException e) {
		}

		return -1;
	}

	/*
	 * @see ICharacterScanner#getLegalLineDelimiters()
	 */
	public final char[][] getLegalLineDelimiters() {
		return fDelimiters;
	}
}
