Item.java

package models;

import java.util.Date;

/**
 * A item owned by a {@link User}.
 * 
 * @author Simon Marti
 * @author Mirco Kocher
 * 
 */
public abstract class Item {

	/** This item's owner (or <code>null</code>). */
	private User owner;

	/** The date this item was created. */
	private Date timestamp;

	/** This item's ID. */
	private final int id;

	/** An auto-incrementing counter for producing unique values as IDs. */
	private static int auto_increment = 0;

	/**
	 * Since there's no ideal place for using an IDTable, we just count through
	 * all items, assigning them an auto-incremented value as ID.
	 * 
	 * @return the next ID value
	 */
	private synchronized int autoIncrementID() {
		return auto_increment++;
	}

	/**
	 * Create an <code>Item</code>, noting the current time and giving it a
	 * unique (auto-incremented) ID. Also, if the item has an owner, this owner
	 * is informed about the creation of the new item.
	 * 
	 * @param owner
	 *            the {@link User} who owns the <code>Item</code>
	 */
	public Item(User owner) {
		this.owner = owner;
		this.timestamp = SysInfo.now();
		this.id = this.autoIncrementID();
		if (owner != null) {
			owner.registerItem(this);
		}
	}

	/**
	 * Get the owner of an <code>Item</code> (legacy-style).
	 * 
	 * @return the owner
	 */
	public User owner() {
		return this.owner;
	}

	/**
	 * Get the time the <code>Item</code> was created (legacy-style).
	 * 
	 * @return the creation date as a UNIX timestamp
	 */
	public Date timestamp() {
		return this.timestamp;
	}

	/**
	 * Sets the timestamp of this <code>Item</code> (for importers only).
	 * 
	 * @param timestamp
	 *            the new timestamp
	 */
	public void setTimestamp(Date timestamp) {
		this.timestamp = timestamp;
	}

	/**
	 * Gets this notification's ID value (legacy-style).
	 * 
	 * @return this item's ID
	 */
	public int id() {
		return this.id;
	}

	/**
	 * Drops all the references this <code>Item</code> has, so that they can be
	 * garbage collected.
	 */
	public void delete() {
		this.unregisterUser();
	}

	/**
	 * Unregisters this <code>Item</code>'s owner so that this item becomes
	 * unowned and informs the owner that this item is no longer his/hers.
	 */
	protected void unregisterUser() {
		if (this.owner != null) {
			this.owner.cleanUp(this);
		}
		this.owner = null;
	}
}