package brs;

/**
 * Represents the empty state of a BiTree.  Uses the singleton pattern to model
 * the uniqueness of "emptiness".
 * @author Dung X. Nguyen - Copyright 2001 - All rights reserved.
 * @since 11/04/01
 */
class EmptyNode extends ANode {
    /**
    * Singleton pattern.
    * @SBGen Variable (singleton,,,0)
    */
    final static EmptyNode Singleton = new EmptyNode ();

    private EmptyNode (){
    }

    /**
    * Throws java.util.NoSuchElementException.
    * @param owner the BiTree holding this EmptyNode.
    */
    Object getRootDat (BiTree owner) {
        throw new java.util.NoSuchElementException ("EmptyNode.getRootDat ()");
    }

    /**
    * Throws java.util.NoSuchElementException.
    * @param dat a data Object.
    * @param owner the BiTree holding this EmptyNode.
    */
    void setRootDat (Object dat, BiTree owner) {
        throw new java.util.NoSuchElementException ("EmptyNode.setRootDat ()");
    }

    /**
    * Throws java.util.NoSuchElementException.
    * @param owner the BiTree holding this EmptyNode.
    */
    BiTree getLeftSubTree (BiTree owner) {
        throw new java.util.NoSuchElementException ("EmptyNode.getLeftSubTree ()");
    }

    /**
    * Throws java.util.NoSuchElementException.
    * @param owner the BiTree holding this EmptyNode.
    */
    BiTree getRightSubTree(BiTree owner) {
        throw new java.util.NoSuchElementException ("EmptyNode.getRightSubTree ()");
    }

    /**
    * Throws java.util.NoSuchElementException.
    * @param biTree a given BiTree.
    * @param owner the BiTree holding this EmptyNode.
    */
    void setLeftSubTree(BiTree biTree, BiTree owner) {
        throw new java.util.NoSuchElementException ("EmptyNode.setLeftSubTree ()");
    }

    /**
    * Throws java.util.NoSuchElementException.
    * @param biTree a given BiTree.
    * @param owner the BiTree holding this EmptyNode.
    */
    void setRightSubTree(BiTree biTree, BiTree owner) {
        throw new java.util.NoSuchElementException ("EmptyNode.setRightSubTree ()");
    }

    /**
    * Asks the owner tree to set the root node to a new DatNode containing dat,
    * resulting in a state change from empty to non-empty.
    * @param dat a given data Object.
    * @param owner the context of this state.
    */
    void insertRoot(Object dat, BiTree owner) {
        owner.setRootNode(new DatNode(dat));
    }

    /**
    * Throws java.util.NoSuchElementException.
    * @param owner the BiTree holding this EmptyNode.
    */
    Object remRoot (BiTree owner) {
        throw new java.util.NoSuchElementException ("EmptyNode.remRoot ()");
    }

    /**
    * Asks oSib to help remove the root node of the parent of owner.
    * Because this node is the EmptyNode, it's up to the sibling of the owner
    * tree to decide whether or not it can help remove the root node of the
    * owner's parent.
    * @param oSib the sibling BiTree owner.
    * @param oDad the parent tree of owner.
    * @param owner the BiTree holding this EmptyNode.
    */
    Object remParent(BiTree oSib, BiTree oDad, BiTree owner) {
        return oSib.remParentNode (oDad);
    }

    /**
    * Removes and returns the root element of the grandparent of this node:
    * because this method is called by an <I>empty</I> sibling of owner, we
    * know at this point that the parent of owner has two empty subtrees.
    * @param owner the BiTree holding this EmptyNode.
    */
    Object remParentNode (BiTree ownerDad, BiTree owner) {
        Object dat = ownerDad.getRootDat();
        ownerDad.setRootNode (EmptyNode.Singleton);
        return dat;
    }

    /**
    * Calls algo's emptyCase () method to execute the algorithm algo.
    * @param algo the visiting algorithm
    * @param inp the input algo needs.
    * @param owner the BiTree holding this EmptyNode.
    * @return the output for the emptyCase() of algo.
    */
    Object execute(IVisitor algo, Object inp, BiTree owner) {
        return algo.emptyCase(owner, inp);
    }
}