/*******************************************************************************
 * Copyright (c) 2004-2008 Andras Schmidt, Andras Balogh, Istvan Rath and Daniel Varro
 * 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:
 *    Andras Schmidt, Andras Balogh, Istvan Rath - initial API and implementation
 *******************************************************************************/

package org.eclipse.viatra2.core.simple.tempdata;

/**
 * Temporary data is valid as long as the state counter of the model
 * (incremented at all model changes) is equal to the state when this temporary
 * data was created. In other words, temporary data is a dependent information
 * on the VPM model.
 * 
 * @author Andras Schmidt
 * 
 */
public class TemporaryData<E> {
	/**
	 * The state when this data is valid.
	 */
	int createdAtState;

	/**
	 * The data stored in this container.
	 */
	E o;

	/**
	 * Instantiate a container
	 * 
	 * @param state
	 *            The state when this data is valid.
	 * @param o
	 *            The data stored in this container.
	 */
	TemporaryData(int state, E o) {
		createdAtState = state;
		this.o = o;
	}

	/**
	 * Instantiate a container with data never valid
	 */
	TemporaryData() {
		createdAtState = -1;
		o = null;
	}

	/**
	 * Check whether the data is valid at curren state.
	 * 
	 * @param currentState
	 *            the state of the VPM model
	 * @return true is data is still valid
	 */
	public boolean isValid(int currentState) {
		if (currentState == createdAtState)
			return o != null;
		else {
			o = null;
			return false;
		}
	}

	/**
	 * The data stored in this container
	 * 
	 * @param currentState
	 *            the state of VPM model
	 * @return The data stored in this container or null if data is not valid
	 */
	public E getObject(int currentState) {
		if (isValid(currentState))
			return o;
		else {
			o = null;
			return null;
		}
	}

	/**
	 * Set the new value of the data
	 * 
	 * @param state
	 *            The state when this data is valid.
	 * @param o
	 *            The data stored in this container.
	 */
	public void setObject(int currentState, E o) {
		//this.discard(); // experimental
		createdAtState = currentState;
		this.o = o;
	}

	/**
	 * Clear this tempdata object
	 * 
	 * @return 1 if this container stored a value. 0 if not.
	 */
	public int discard() {
		Object oldo = o;
		o = null;
		if (oldo != null)
			return 1;
		else
			return 0;
	}
}