package brs.visitor;

import brs.*;
import ordering.*;

/**
* Inserts an IOrdered into the host maintaining the host's binary search tree
* property.
* Duplication is not allowed: replaces old data object with the new one.

Suppose we have a set of objects that can be compared for equality with
"equal to"
and "totally ordered" with an order relation called "less or equal to" .
Define "less than" to mean "less or equal to" AND "not equal to".
Let T be a BiTree structure that stores such totally ordered objects.
Definition:
T is said to satisfy the binary search tree property (BSTP) if
  T is empty, or
  when T is not empty, the left and right subtrees of T both satisfy BSTP, and
  all elements in the left subtree of T are less than the root of T, and
  the root of T is less than all elements in the right subtree of T.


* @author Dung X. Nguyen - Copyright 2001 - All rights reserved.
*/
public class BSTInserter implements IVisitor {
    private AOrder _order;

    public  BSTInserter (AOrder order) {
        _order = order;
    }

    /**
    * Returns the host tree where the input is inserted as the root.
    * @param host an empty binary tree, which obviously satisfies BSTP.
    * @param input new data to be inserted.
    * @return host (which is no longer empty).
    */
    public Object emptyCase(BiTree host, Object input) {
        host.insertRoot (input);
        return host;
    }

    /**
    * If order.eq (input, host.getRootDat) then the old root data is replaced
    * by input.
    * @param host non-empty and satisfies BSTP.
    * @param input new data to be inserted.
    * @return the tree where input is inserted as the root.
    */
    public Object nonEmptyCase(BiTree host, Object input) {
        Object root = host.getRootDat();
        if (_order.lt(input, root)) {
            return host.getLeftSubTree().execute(this, input);
        }
        if (_order.eq (input, root)) {
            host.setRootDat(input);
            return host;
        }
        return host.getRightSubTree().execute(this, input);
    }
}