org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/text/LineBreakingReader.java

/*******************************************************************************
 * Copyright (c) 2000, 2006 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jdt.internal.ui.text;


import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;

import com.ibm.icu.text.BreakIterator;
import org.eclipse.swt.graphics.GC;

/*
 * Not a real reader. Could change if requested
 */
public class LineBreakingReader {

	private BufferedReader fReader;
	private GC fGC;
	private int fMaxWidth;

	private String fLine;
	private int fOffset;

	private BreakIterator fLineBreakIterator;
	private boolean fBreakWords;

	/**
	 * Creates a reader that breaks an input text to fit in a given width.
	 * 
	 * @param reader Reader of the input text
	 * @param gc The graphic context that defines the currently used font sizes
	 * @param maxLineWidth The max width (pixels) where the text has to fit in
	 */
	public LineBreakingReader(Reader reader, GC gc, int maxLineWidth) {
		fReader= new BufferedReader(reader);
		fGC= gc;
		fMaxWidth= maxLineWidth;
		fOffset= 0;
		fLine= null;
		fLineBreakIterator= BreakIterator.getLineInstance();
		fBreakWords= true;
	}

	public boolean isFormattedLine() {
		return fLine != null;
	}

	/**
	 * Reads the next line. The lengths of the line will not exceed the given maximum
	 * width.
	 * 
	 * @return the next line 
	 * @throws IOException 
	 */
	public String readLine() throws IOException {
		if (fLine == null) {
			String line= fReader.readLine();
			if (line == null)
				return null;

			int lineLen= fGC.textExtent(line).x;
			if (lineLen < fMaxWidth) {
				return line;
			}
			fLine= line;
			fLineBreakIterator.setText(line);
			fOffset= 0;
		}
		int breakOffset= findNextBreakOffset(fOffset);
		String res;
		if (breakOffset != BreakIterator.DONE) {
			res= fLine.substring(fOffset, breakOffset);
			fOffset= findWordBegin(breakOffset);
			if (fOffset == fLine.length()) {
				fLine= null;
			}
		} else {
			res= fLine.substring(fOffset);
			fLine= null;
		}
		return res;
	}

	private int findNextBreakOffset(int currOffset) {
		int currWidth= 0;
		int nextOffset= fLineBreakIterator.following(currOffset);
		while (nextOffset != BreakIterator.DONE) {
			String word= fLine.substring(currOffset, nextOffset);
			int wordWidth= fGC.textExtent(word).x;
			int nextWidth= wordWidth + currWidth;
			if (nextWidth > fMaxWidth) {
				if (currWidth > 0)
					return currOffset;

				if (!fBreakWords)
					return nextOffset;

				// need to fit into fMaxWidth
				int length= word.length();
				while (length >= 0) {
					length--;
					word= word.substring(0, length);
					wordWidth= fGC.textExtent(word).x;
					if (wordWidth + currWidth < fMaxWidth)
						return currOffset + length;
				}
				return nextOffset;
			}
			currWidth= nextWidth;
			currOffset= nextOffset;
			nextOffset= fLineBreakIterator.next();
		}
		return nextOffset;
	}

	private int findWordBegin(int idx) {
		while (idx < fLine.length() && Character.isWhitespace(fLine.charAt(idx))) {
			idx++;
		}
		return idx;
	}
}