/*****************************************************************
 * Bag class implemented with a linked list - data are generic
 * Roughly based on bag in text by Michael Main but simplified
 * @author Beth Katz
 * @version March 2008
 *****************************************************************/

public class BagLL<E> implements Cloneable {
	// class invariant
	// - there are two instance variables: head and itemCount
	// - head is head reference to a linked list containing
	//      String data; null if there are no items
	// - itemCount is how many items are in the list
	
	private Node<E> head;
	private int itemCount; // text calls this manyNodes
	
	/**
	 * Constructs an empty bag
	 */
	public BagLL( ) {
		head = null;
		itemCount = 0;
	}
	
	/** 
	 * Add item to bag
	 * @param item
	 *    item to be added
	 */
	public void add(E item) {
		head = new Node<E>(item, head);
		itemCount++;
	}
	
	/**
	 * Removes target from the bag returning whether it was successful
	 * @param target
	 *    the item to be removed
	 * @return
	 *    whether or not removal was successful
	 */
	public boolean remove(E target) {
		Node<E> cursor = head;
		while (cursor != null && !(cursor.getData( )).equals(target)) { 
			cursor = cursor.getLink( );			
		}
		if (cursor == null) { // not found
			return false; 
		} else { // move value from head here and chop off head
			     // know there is head because target was found
			cursor.setData(head.getData( ));
			head = head.getLink( );
			itemCount--;
			return true;
		}
	}

	/**
	 * Returns a separate copy of this BagLLstring that will appear
	 * to be indistinguishable from the original but separate
	 * Follows pattern on p. 83 of text
	 * @postcondition
	 *   The returned BagLLstring is a separate copy of this BagLLstring
	 */
	public BagLL<E> clone( ) {	
		BagLL<E> answer;
		try {
			answer = (BagLL<E>) super.clone( );  // unavoidable warning - ignore
			
			// make a separate copy
			Node<E> cursor, answerCursor;
			if (head != null) { // have something to copy
				// make front of answer list
				answer.head = new Node<E>(head.getData( ), null);
				answerCursor = answer.head;
				
				cursor = head.getLink( ); // move to next node
				
				while (cursor != null) {
					answerCursor.setLink(new Node<E>(cursor.getData( ), null));
					answerCursor = answerCursor.getLink( );
					cursor = cursor.getLink( );
				}
			}
		}
		catch (CloneNotSupportedException e) {
			throw new RuntimeException("This class does not implement Cloneable.");
		}
		return answer;
	}
		
	/**
	 * Returns a neat horizontal string representation of the 
	 * bag's contents
	 * @return
	 *    string of bag contents
	 */
	public String toString( ) {
		Node<E> cursor;
		String answer = "#Items=" + itemCount + " Contents: ";

		for (cursor = head; cursor != null; cursor = cursor.getLink( )) {
		    answer += cursor.getData( ) + " ";
		}
		return answer;
	}
	
}