/*
 * Copyright (c) 2009-2012 jMonkeyEngine
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * * Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * * Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 *
 * * Neither the name of 'jMonkeyEngine' nor the names of its contributors
 *   may be used to endorse or promote products derived from this software
 *   without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.jme3.math;

/**
 * Temporary variables assigned to each thread. Engine classes may access these
 * temp variables with TempVars.get(), all retrieved TempVars instances must be
 * returned via TempVars.release(). This returns an available instance of the
 * TempVar class ensuring this particular instance is never used elsewhere in
 * the mean time.
 */
public class TempVars {

	/**
	 * Allow X instances of TempVars in a single thread.
	 */
	private static final int STACK_SIZE = 5;

	/**
	 * <code>TempVarsStack</code> contains a stack of TempVars. Every time
	 * TempVars.get() is called, a new entry is added to the stack, and the
	 * index incremented. When TempVars.release() is called, the entry is
	 * checked against the current instance and then the index is decremented.
	 */
	private static class TempVarsStack {

		int index = 0;
		TempVars[] tempVars = new TempVars[STACK_SIZE];
	}

	/**
	 * ThreadLocal to store a TempVarsStack for each thread. This ensures each
	 * thread has a single TempVarsStack that is used only in method calls in
	 * that thread.
	 */
	private static final ThreadLocal<TempVarsStack> varsLocal = new ThreadLocal<TempVarsStack>() {

		@Override
		public TempVarsStack initialValue() {
			return new TempVarsStack();
		}
	};
	/**
	 * This instance of TempVars has been retrieved but not released yet.
	 */
	private boolean isUsed = false;

	private TempVars() {
	}

	/**
	 * Acquire an instance of the TempVar class. You have to release the
	 * instance after use by calling the release() method. If more than
	 * STACK_SIZE (currently 5) instances are requested in a single thread then
	 * an ArrayIndexOutOfBoundsException will be thrown.
	 * 
	 * @return A TempVar instance
	 */
	public static TempVars get() {
		TempVarsStack stack = varsLocal.get();

		TempVars instance = stack.tempVars[stack.index];

		if (instance == null) {
			// Create new
			instance = new TempVars();

			// Put it in there
			stack.tempVars[stack.index] = instance;
		}

		stack.index++;

		instance.isUsed = true;

		return instance;
	}

	/**
	 * Releases this instance of TempVars. Once released, the contents of the
	 * TempVars are undefined. The TempVars must be released in the opposite
	 * order that they are retrieved, e.g. Acquiring vars1, then acquiring
	 * vars2, vars2 MUST be released first otherwise an exception will be
	 * thrown.
	 */
	public void release() {
		if (!isUsed) {
			throw new IllegalStateException("This instance of TempVars was already released!");
		}

		isUsed = false;

		TempVarsStack stack = varsLocal.get();

		// Return it to the stack
		stack.index--;

		// Check if it is actually there
		if (stack.tempVars[stack.index] != this) {
			throw new IllegalStateException(
				"An instance of TempVars has not been released in a called method!"
			);
		}
	}

	/**
	 * General vectors.
	 */
	public final Vector3f vect1 = new Vector3f();
	public final Vector3f vect2 = new Vector3f();
	public final Vector3f vect3 = new Vector3f();
	/**
	 * General matrices.
	 */
	public final Matrix4f tempMat4 = new Matrix4f();

	public final float[] matrixWrite = new float[16];
}