package de.thpeetz.tools;

import java.util.Vector;
import java.util.logging.Level;
import java.util.logging.Logger;

import de.thpeetz.network.osi.transport.RFC1006Service;

/**
 * @author Thomas Peetz
 *
 * @param <T> type of objects in ObjectPool
 */
public class ObjectPool<T> {
    /**
     * Vector of unused object references.
     */
    private final Vector<T> freeStack;

    Logger logger;

    /**
     * Construct an object pool for a specific class type.
     *
     * @param clazz
     *            Class type of object pool
     * @throws IllegalAccessException
     * @throws InstantiationException
     */
    public ObjectPool(final Class<T> clazz) {
        this.freeStack = new Vector<T>();
        init(clazz);
        logger = Logger.getLogger(ObjectPool.class.getName());

    }

    /**************************************************************************
     * Construct an object pool for a specific class type. Initialize object
     * pool with given number of objects.
     *
     * @param clazz
     *            Class type of object pool
     * @param size
     *            Initial number of objects in pool
     * @throws IllegalAccessException
     * @throws InstantiationException
     ***************************************************************************/
    public ObjectPool(final Class<T> clazz, final int size) {
        this.freeStack = new Vector<T>(size);
        init(clazz);
    }

    /**************************************************************************
     * Construct an object pool for a specific class type. Initialize object
     * pool with number of objects equal to stack size.
     *
     * @param clazz
     *            Class type of object pool
     ***************************************************************************/
    private void init(final Class<T> clazz) {
        for (int i = 0; i < freeStack.capacity(); i++) {
            try {
                freeStack.add(i, clazz.newInstance());
            } catch (InstantiationException e) {
                logger.log(Level.FINE, e.getMessage());
            } catch (IllegalAccessException e) {
                logger.log(Level.FINE, e.getMessage());
            }
        }
    }

    /**
     * Get instance from object pool.
     *
     * @return Reference of object
     */
    public final synchronized T getInstance() {
        // Check if the pool is empty.
        if (this.freeStack.isEmpty()) {
            return null;
        }
        // Remove object from end of free pool.
        T result = this.freeStack.lastElement();
        this.freeStack.setSize(this.freeStack.size() - 1);
        return result;
    }

    /**************************************************************************
     * Return object to object pool.
     *
     * @param obj
     *            Reference of unsed object
     ***************************************************************************/
    public final synchronized void freeInstance(final T obj) {
        this.freeStack.addElement(obj);
    }
}