/*
 Copyright (C) 2008 Richard Gomes

 This source code is release under the BSD License.

 This file is part of JQuantLib, a free-software/open-source library
 for financial quantitative analysts and developers - http://jquantlib.org/

 JQuantLib is free software: you can redistribute it and/or modify it
 under the terms of the JQuantLib license.  You should have received a
 copy of the license along with this program; if not, please email
 . The license is also available online at
 .

 This program is distributed in the hope that it will be useful, but WITHOUT
 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 FOR A PARTICULAR PURPOSE.  See the license for more details.

 JQuantLib is based on QuantLib. http://quantlib.org/
 When applicable, the original copyright notice follows this notice.
 */



package org.jquantlib.math.randomnumbers;




/**
 * Random seed generator
 * 

 * Random number generator used for automatic generation of initialization seeds.
 *
 * @author Dominik Holenstein
 *
 **/
//TEST: write test cases
public class SeedGenerator {

	//
	// private static fields
	//

    /**
     * @see The "Double-Checked Locking is Broken" Declaration 
     */
	private static volatile SeedGenerator instance;


	//
	// private fields
	//

	private MersenneTwisterUniformRng rng;


	//
	// private constructor
	//

	private SeedGenerator() {
        if (System.getProperty("EXPERIMENTAL")==null) {
            throw new UnsupportedOperationException("Work in progress");
        }
		this.rng = new MersenneTwisterUniformRng(42);
		initialize();
	}


	//
	// private methods
	//

	private void initialize() {

		// firstSeed is chosen based on Date and used for the first rng
		final long firstSeed = System.currentTimeMillis();
		final MersenneTwisterUniformRng first = new MersenneTwisterUniformRng(firstSeed);

		// secondSeed is as random as it could be
		// feel free to suggest improvements
	 	final long secondSeed = first.nextInt32();
		final MersenneTwisterUniformRng second = new MersenneTwisterUniformRng(secondSeed);

		// use the second rng to initialize the final one
		final long skip = second.nextInt32() % 1000;
		final int init[] = new int[4];
		init[0] = (int) second.nextInt32();
		init[1] = (int) second.nextInt32();
		init[2] = (int) second.nextInt32();
		init[3] = (int) second.nextInt32();

		this.rng = new MersenneTwisterUniformRng(init);

		for (long i=0; i