ColourManager.java

package net.sourceforge.pmd.eclipse.util;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import net.sourceforge.pmd.util.StringUtil;

import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.graphics.RGB;
import org.eclipse.swt.widgets.Display;

/**
 * A singleton that manages colour resources.
 * 
 * @author Brian Remedios
 */
public class ColourManager {

	private final Display display;
	
	private final Map<RGB, Color> coloursByRGB = new HashMap<RGB, Color>();
	
	private static ColourManager instance;

	private ColourManager(Display theDisplay) {
		display = theDisplay;
	}

	public static ColourManager managerFor(Display display) {
	    
	    if (instance == null) instance = new ColourManager(display);
	    return instance;
	}

	public Color colourFor(RGB colourFractions) {
	    
	    Color colour = coloursByRGB.get(colourFractions);
        if (colour != null) return colour;
        
        colour = new Color(display, colourFractions.red, colourFractions.green, colourFractions.blue);
        coloursByRGB.put(colourFractions, colour);
        return colour;
	}
	
	/**
	 * Derive a colour from the input text after slicing it into three
	 * sections and taking the log of their hashes and smushing them
	 * into RGB values
	 * 
	 * @param text
	 * @return Color
	 */
	public Color colourFor(String text) {
		
		if (StringUtil.isEmpty(text)) return display.getSystemColor(SWT.COLOR_WHITE);
		
		text = text.trim();
		int length = text.length();
		
		if (length < 3) return  display.getSystemColor(SWT.COLOR_WHITE);
		
		int posA = length / 3;
		int posB = posA * 2;
				
		int rHash = text.subSequence(0, posA).hashCode();
		int gHash = text.subSequence(posA, posB).hashCode();
		int bHash = text.subSequence(posB, length).hashCode();
		
		RGB colourFractions = new RGB(
			(int)(Math.log10(rHash) % 1 * 255),
			(int)(Math.log10(gHash) % 1 * 255),
			(int)(Math.log10(bHash) % 1 * 255)
			);
		
		return colourFor(colourFractions);
	}
	
	public void dispose() {
		
		Iterator<Color> iter = coloursByRGB.values().iterator();
		while (iter.hasNext()) iter.next().dispose();
	}
}