package funpoly;

import funpoly.visitor.IVisitor;

/**
 *
 * Serves as a factory for manufacturing Polynomial objects.
 * @author Dung X. Nguyen
 * @since December 28, 1999
  */
public class PolyFactory
{
   /** @SBGen Variable (,Zero Polynomial,,64)   */
	public final static APolynomial ZeroPoly = new ConstPoly (0);
   /**
   * Creates a constant Polynomial.  Uses the flyweight pattern for the zero polynomial.
   * @return a constant Polynomial.
   */
   public static APolynomial MakeConstPoly (int coef)
   {
      return 0 == coef? ZeroPoly: new ConstPoly (coef);
   }

   /**
   * Creates a non-constant Polynomial with a given leading coefficient, a given degree,
   * and a given lower order polynomial.  Checks for legal input parameters.
   * Will ignore zero leading coefficient.
   * @param coef the leading coefficient.
   * @param degree the degree, >= 0.
   * @param lowPoly != null, the lower ordered polynomial with degree < degree.
   * @return a non-constant Polynomial.
   * @exception throws IllegalArgumentException if conditions on degree and lowerPoly are violated.
   */
   public static APolynomial MakePoly (int coef, int degree, APolynomial lowerPoly)
   {
      if (degree <= 0)
      {
         throw new IllegalArgumentException ("Degree must be positive!");
      }
      if (null == lowerPoly)
      {
         throw new IllegalArgumentException ("lowerPoly must be non-null!");
      }
      if (0 == coef)
      {
         return lowerPoly;
      }
      if (degree <= lowerPoly.getDegree())
      {
         throw new IllegalArgumentException ("lowPoly is not a lower order term!");
      }
      return new NonConstPoly (coef, degree, lowerPoly);
   }

   /**
   * A few simple test cases.
   */
   public static void main (String[] args)
   {
      APolynomial pc0 = ZeroPoly;
      APolynomial pc1 = MakeConstPoly (-1);
      APolynomial p1 = MakePoly (-5, 3, pc0);
      APolynomial p2 = MakePoly (2, 5, p1);
      APolynomial p3 = MakePoly (-4, 6, p2);
      APolynomial p4 = MakePoly (3, 2, pc1);
      System.out.println ("0  = " + pc0);
      System.out.println ("-1 = " + pc1);
      System.out.println ("3x^2 - 1  = " + p4);
      System.out.println ("-5x^3 + 0 = " + p1);
      System.out.println ("2x^5 - 5x^3 + 0          = " + p2);
      System.out.println ("-4x^6 + 2x^5 - 5x^3 + 0  = " + p3);
   }
}