ltk/org.eclipse.statet.ltk.core/src/org/eclipse/statet/ecommons/text/core/rules/BufferedDocumentScanner.java

/*=============================================================================#
 # Copyright (c) 2000, 2020 IBM Corporation and others.
 # 
 # This program and the accompanying materials are made available under the
 # terms of the Eclipse Public License 2.0 which is available at
 # https://www.eclipse.org/legal/epl-2.0.
 # 
 # SPDX-License-Identifier: EPL-2.0
 # 
 # Contributors:
 #     IBM Corporation - org.eclipse.jdt: initial API and implementation
 #     Stephan Wahlbrink <sw@wahlbrink.eu> - initial API and implementation
 #=============================================================================*/

package org.eclipse.statet.ecommons.text.core.rules;

import org.eclipse.core.runtime.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(final int size) {
		Assert.isTrue(size >= 1);
		this.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(final int offset) {
		this.fBufferOffset= offset;
		
		if (this.fBufferOffset + this.fBuffer.length > this.fRangeOffset + this.fRangeLength) {
			this.fBufferLength= this.fRangeLength - (this.fBufferOffset - this.fRangeOffset);
		} else {
			this.fBufferLength= this.fBuffer.length;
		}
		
		try {
			final String content= this.fDocument.get(this.fBufferOffset, this.fBufferLength);
			content.getChars(0, this.fBufferLength, this.fBuffer, 0);
		} catch (final 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(final IDocument document, final int offset, final int length) {
		this.fDocument= document;
		this.fRangeOffset= offset;
		this.fRangeLength= length;
		
		final String[] delimiters= document.getLegalLineDelimiters();
		this.fDelimiters= new char[delimiters.length][];
		for (int i= 0; i < delimiters.length; i++) {
			this.fDelimiters[i]= delimiters[i].toCharArray();
		}
		
		updateBuffer(offset);
		this.fOffset= 0;
	}
	
	@Override
	public final int read() {
		if (this.fOffset >= this.fBufferLength) {
			if (this.fBufferOffset + this.fBufferLength >= this.fRangeOffset + this.fRangeLength) {
				return EOF;
			} else {
				updateBuffer(this.fBufferOffset + this.fBufferLength);
				this.fOffset= 0;
			}
		}
		return this.fBuffer[this.fOffset++];
	}
	
	@Override
	public final void unread() {
		if (this.fOffset <= 0) {
			if (this.fBufferOffset <= this.fRangeOffset) {
				// error: BOF
			} else {
				updateBuffer(this.fBufferOffset - this.fBuffer.length);
				this.fOffset= this.fBuffer.length - 1;
			}
		} else {
			--this.fOffset;
		}
	}
	
	@Override
	public final int getColumn() {
		try {
			final int offset= this.fBufferOffset + this.fOffset;
			final int line= this.fDocument.getLineOfOffset(offset);
			final int start= this.fDocument.getLineOffset(line);
			return offset - start;
		} catch (final BadLocationException e) {
		}
		
		return -1;
	}
	
	@Override
	public final char[][] getLegalLineDelimiters() {
		return this.fDelimiters;
	}
	
}