import java.util.Enumeration;
import java.util.Hashtable;

public class ShoppingBasketImpl implements ShoppingBasket {
    private Hashtable           m_basket;
    private ItemFactory         m_itemFactory;

    public ShoppingBasketImpl(ItemFactory itemFactory) {
	Util.assert(itemFactory != null, "Null Item Factory is not allowed");

	m_basket      = new Hashtable();
	m_itemFactory = itemFactory;
	
    }

    public void addItem(Item newItem) {
	Util.assert(newItem != null, "Invalid newItem to add to Basket");

	int  newQuantity = 0;
	Item oldItem     = (Item) m_basket.remove(newItem.getItemId());
	
	/* If newItem is not in the shopping basket (ie. oldItem==null) then 
	 * we add it.
	 * Otherwise, we add a BRAND NEW item
	 * whose quantity is newItem.quantity + oldItem.quantity
	 */
	if (oldItem == null) {
	    m_basket.put(newItem.getItemId(), newItem);
	} 
	else {
	    /* Notice that oldItem.equals(newItem) is true which
	     * means that unit price, id, name are the same for both
	     * oldItem and newItem.
	     *
	     * We remove the old item and add in a new one. Why don't
	     * we just get the old one and modify it?  Because someone 
	     * could modify ItemImpl.hashCode() so that it depends
	     * on quantity.
	     */
	    newQuantity = oldItem.getQuantity() + newItem.getQuantity();

	    Item item = 
		m_itemFactory.createItem(
		     oldItem.getItemId(),     // same as newItem.getItemId()
		     oldItem.getItemName(),   // same as newItem.getItemName()
		     newQuantity,
		     oldItem.getUnitPrice()); // same as newItem.getUnitPrice()

	    m_basket.put(item.getItemId(), item);
	}
    } //end addItem

    public void removeItem(Item deletedItem) {
	/* We remove the item and add it back in if necessary because
	 * the hashCode might change.
	 */

	int  newQuantity = 0;
	Item removedItem = (Item) m_basket.remove(deletedItem.getItemId());

	Util.assert(removedItem != null, 
		    "Tried to remove an item that is not in the basket");

	newQuantity = removedItem.getQuantity() - deletedItem.getQuantity();

	Util.assert(newQuantity >= 0,
		    "Tried to remove more " + removedItem.getItemName() + "s" +
		    " then actually exist in the basket");

	if (newQuantity > 0) {
	    Item item = m_itemFactory.createItem(removedItem.getItemId(),
						 removedItem.getItemName(),
						 newQuantity,
						 removedItem.getUnitPrice());

	    m_basket.put(item.getItemId(), item);
	}
    } //end removeItem


    public Enumeration elements() {
	return m_basket.elements();
    }


    public String toString() {
	float total = 0.0F;
	Enumeration e = m_basket. elements ();
	String r = "";
	Item anItem;
	while (e. hasMoreElements ())
	{
	    anItem = (Item) e. nextElement ();
	    total = total + anItem. getTotalPrice ();
	    r = r + anItem. toString () + "\n";
	}
	r = r + "TOTAL: $" + total;
	return r;
    }

}