package poly.visitor;

import poly.*;

/**
* Adds host polynomial to input polynomial.  Returns the resulting sum polynomial.
 <pre>
 * Copyright 2000, by Dung X. Nguyen, All rights reserved.
 </pre>
 * @author Dung X. Nguyen
 * @since 10/19/2000
*/
public class Add implements IVisitor
{
   public static final Add Singleton = new Add ();

	private Add ()
	{
	}
	/**
    * Uses the helper visitor AddConst to add a constant to the input APolynomial.
	 * @param poly a Constant polynomial
	 * @param rhs the polynomial to be added to poly
	 * @return a APolynomial representing the sum of poly and rhs.
	 */
	public Object forConst (ConstPoly poly, Object rhs)
	{
      return ((APolynomial)rhs).execute (new AddConst (poly.getLeadCoef()), null);
	}

	/**
	 * @param poly a non-constant APolynomial
	 * @param rhs the polynomial to be added to poly
	 * @return a APolynomial representing the sum of poly and rhs.
	 */
	public Object forNonConst(NonConstPoly poly, Object rhs)
	{
      APolynomial p = (APolynomial)rhs;
      double pCoef = p.getLeadCoef();
      int pDegree = p.getDegree();
      double polyCoef = poly.getLeadCoef();
      int polyDegree = poly.getDegree();
      if (pDegree < polyDegree)
      {
         return new NonConstPoly (polyCoef, polyDegree, (APolynomial)poly.getLowerPoly().execute (this, p));
      }
      else if (pDegree == polyDegree)
      {
         double coef = polyCoef + pCoef;
         APolynomial lowerSum = (APolynomial)poly.getLowerPoly().execute(this, p.getLowerPoly());
         return 0.0 == coef? // IMPORTANT!
                  lowerSum:
                  new NonConstPoly (coef, polyDegree, lowerSum);
      }
      else
      {
         return new NonConstPoly (pCoef, pDegree, (APolynomial)poly.execute(this, p.getLowerPoly()));
      }
	}
}