/**
 *
 */
package de.fhswf.in.inf.upnfx.util;


/**
 * A class that calculates in UPN.
 *
 * @author $Author: $
 * @version $Revision: $, $Date: $ UTC
 */
public class UPN
{

   private ObservableDoubleStack upnStack = new ObservableDoubleStack();

   private Double lastX;

   /**
    * Empty constructor.
    *
    */
   public UPN()
   {
   }

   /**
    * Reads a string and puts it on the UPN upnStack.
    *
    * @param upnString
    *           A space delimited string in UPN notation.
    */
   public final void calculate(Operator operator)
   {
      if (operator == null)
      {
         throw new IllegalArgumentException("Operator can't be null.");
      }
      
      System.out.println(operator);
      
      lastX = upnStack.peek();

      operator.eval(upnStack);

   }
   
   public final void addDouble(Double newVal)
   {
      if (newVal == null)
      {
         throw new IllegalArgumentException("newVal can't be null.");
      }
      upnStack.push(newVal);
   }

   /**
    * Get the result of a calculation done before.
    *
    * @return The top most value on the UPN stack.
    */
   public final double getResult()
   {
      if (upnStack.isEmpty())
      {
         throw new IllegalArgumentException("UPN stack is empty.");
      }
      return upnStack.peek();
   }

   /**
    * Return the ObservableDoubleStack to tie it to the view.
    *
    * @return The ObservableDoubleStack with the operands.
    */
   public final ObservableDoubleStack getStack()
   {
      return upnStack;
   }

   /**
    * Pushes the previous x onto the stack.
    *
    */
   public final void setLastX()
   {
      if(lastX != null)
      {
         upnStack.push(lastX);
      }
   }

   /**
    * Swap x and y on the stack.
    *
    */
   public final void swapXY()
   {
      if(upnStack.size() > 1)
      {
         double f1 = upnStack.pop();
         double f2 = upnStack.pop();

         upnStack.push(f1);
         upnStack.push(f2);
      }
   }

}