package org.nusco.narjillos.shared.utilities;

import java.lang.reflect.Field;
import java.util.Random;
import java.util.concurrent.atomic.AtomicLong;

/**
 * Generates pseudo-random numbers.
 * 
 * A bit like java.math.Random, but strictly deterministic. You must give it a
 * seed during construction, and you cannot call the same instance from multiple
 * threads.
 */
public class RanGen {

	private final TransparentRanGen random = new TransparentRanGen();
	private transient Thread authorizedThread;

	public RanGen(long seed) {
		random.setSeed(seed);
		authorizedThread = Thread.currentThread();
	}

	public double nextDouble() {
		checkThreadIsAuthorized();
		return random.nextDouble();
	}

	public int nextInt() {
		checkThreadIsAuthorized();
		return random.nextInt();
	}

	public int nextByte() {
		return Math.abs(nextInt()) % 255;
	}

	public long getSeed() {
		return random.getSeed();
	}

	private synchronized void checkThreadIsAuthorized() {
		// I apologize for this slightly paranoid defensive code. Bugs with
		// non-deterministic random generators are hard to find, so I have to be
		// extra careful here.

		if (authorizedThread == null) {
			// If the RanGen has been deserialized, the authorized thread
			// could still be null. In this case, the first thread that
			// accesses it wins the role.
			authorizedThread = Thread.currentThread();
			return;
		}

		if (Thread.currentThread() != authorizedThread)
			throw new RuntimeException("RanGen accessed from multiple threads. " + getExplanation());
	}

	private static String getExplanation() {
		return "(Don't do that, or else there is no guarantee that the same " + "seed will generate the same sequence of numbers.)";
	}
}

// A Random that allows you to get/set the current seed.
class TransparentRanGen extends Random {

	private static final long serialVersionUID = 1L;

	public long getSeed() {
		return extractSeed().get();
	}

	public void setSeed(long seed) {
		extractSeed().set(seed);
	}

	private AtomicLong extractSeed() {
		// Put on your gloves - this is going to be dirty.
		try {
			Field seedField = Random.class.getDeclaredField("seed");
			seedField.setAccessible(true);
			return (AtomicLong) seedField.get(this);
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}
}
package org.nusco.narjillos.shared.utilities;

import java.lang.reflect.Field;
import java.util.Random;
import java.util.concurrent.atomic.AtomicLong;

/**
 * Generates pseudo-random numbers.
 * 
 * A bit like java.math.Random, but strictly deterministic. You must give it a
 * seed during construction, and you cannot call the same instance from multiple
 * threads.
 */
public class RanGen {

	private final TransparentRanGen random = new TransparentRanGen();
	private transient Thread authorizedThread;

	public RanGen(long seed) {
		random.setSeed(seed);
		authorizedThread = Thread.currentThread();
	}

	public double nextDouble() {
		checkThreadIsAuthorized();
		return random.nextDouble();
	}

	public int nextInt() {
		checkThreadIsAuthorized();
		return random.nextInt();
	}

	public int nextByte() {
		return Math.abs(nextInt()) % 256;
	}

	public long getSeed() {
		return random.getSeed();
	}

	private synchronized void checkThreadIsAuthorized() {
		// I apologize for this slightly paranoid defensive code. Bugs with
		// non-deterministic random generators are hard to find, so I have to be
		// extra careful here.

		if (authorizedThread == null) {
			// If the RanGen has been deserialized, the authorized thread
			// could still be null. In this case, the first thread that
			// accesses it wins the role.
			authorizedThread = Thread.currentThread();
			return;
		}

		if (Thread.currentThread() != authorizedThread)
			throw new RuntimeException("RanGen accessed from multiple threads. " + getExplanation());
	}

	private static String getExplanation() {
		return "(Don't do that, or else there is no guarantee that the same " + "seed will generate the same sequence of numbers.)";
	}
}

// A Random that allows you to get/set the current seed.
class TransparentRanGen extends Random {

	private static final long serialVersionUID = 1L;

	public long getSeed() {
		return extractSeed().get();
	}

	public void setSeed(long seed) {
		extractSeed().set(seed);
	}

	private AtomicLong extractSeed() {
		// Put on your gloves - this is going to be dirty.
		try {
			Field seedField = Random.class.getDeclaredField("seed");
			seedField.setAccessible(true);
			return (AtomicLong) seedField.get(this);
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}
}
Fix minor bug in random byte generation