package lrs;

/**
 * Represents the abstract list state.
 * @author Dung X. Nguyen  Copyright 2000 - All rights reserved.
 * @author Alan L. Cox
 * @since 02/13/01
 */
abstract class ANode
{
    /**
     * Converts the LRStruct to a String.
     *
     * @param owner the LRStruct referencing this ANode.
     * @return the String describing this ANode.
     */
    String toString(LRStruct owner)
    {
	return (String)owner.execute(
	    new IAlgo()
	    {
		public Object emptyCase(LRStruct host, Object input)
		{
		    return "()";
		}

		public Object nonEmptyCase(LRStruct host, Object input)
		{
		    return "(" + host.getFirst() + host.getRest().execute(
			new IAlgo()
			{
			    public Object emptyCase(LRStruct h, Object inp)
			    {
				return ")";
			    }

			    public Object nonEmptyCase(LRStruct h, Object inp)
			    {
				return " " + h.getFirst() +
				    h.getRest().execute(this, null);
			    }
			}, null);
		}
	    }, null);
    }

    /**
     * Returns the first data object of the referencing LRStruct.
     *
     * @param owner the LRStruct referencing this ANode.
     * @return the tail LRStruct of owner.
     * @throw java.util.NoSuchElementException if empty.
     */
    abstract Object getFirst(LRStruct owner);

    /**
     * Sets a new first data object for the referencing LRStruct.
     *
     * @param data the new data object for this ANode.
     * @param owner the LRS referencing this ANode.
     * @throw java.util.NoSuchElementException if empty.
     */
    abstract void setFirst(Object data, LRStruct owner);

    /**
     * Returns the tail LRStruct of the referencing LRStruct.
     *
     * @param owner the LRStruct referencing this ANode.
     * @return the tail LRStruct of owner.
     * @throw java.util.NoSuchElementException if empty.
     */
    abstract LRStruct getRest(LRStruct owner);

    /**
     * Sets a new tail for the referencing LRStruct.
     *
     * @param tail the new tail for the owner LRStruct.
     * @param owner the LRS referencing this ANode.
     * @throw java.util.NoSuchElementException if empty.
     */
    abstract void setRest(LRStruct tail, LRStruct owner);

    /**
     * Inserts a data object at the front of the LRStruct owner.
     *
     * @param data the object to be inserted at the front.
     * @param owner the LRS referencing this ANode.
     */
    abstract void insertFront(Object data, LRStruct owner);

    /**
     * Removes and returns the first data object for the referencing LRStruct.
     *
     * @param owner the LRS referencing this ANode.
     * @return the front data of the LRStruct owner.
     * @throw java.util.NoSuchElementException if empty.
     */
    abstract Object removeFront(LRStruct owner);

    /**
     * Executes an algorithm and returns the output.
     *
     * @param visitor the algorithm to be executed.
     * @param input the input needed by the algorithm.
     * @param owner the LRStruct referencing this ANode.
     */
    abstract Object execute(IAlgo visitor, Object input, LRStruct owner);
}