/**
    * Logback: the reliable, generic, fast and flexible logging framework.
    * Copyright (C) 1999-2011, QOS.ch. All rights reserved.
    *
    * This program and the accompanying materials are dual-licensed under
    * either the terms of the Eclipse Public License v1.0 as published by
    * the Eclipse Foundation
    *
    *   or (per the licensee's choosing)
   *
   * under the terms of the GNU Lesser General Public License version 2.1
   * as published by the Free Software Foundation.
   */
  package chapters.onJoran.calculator;
  
  import org.xml.sax.Attributes;
  
  import ch.qos.logback.core.joran.action.Action;
  import ch.qos.logback.core.joran.spi.InterpretationContext;
  
  import java.util.EmptyStackException;
  
  /**
   * 
   * This action multiplies the two integers at the top of the stack (they are
   * removed) and pushes the result on top the stack.
   * 
   * @author Ceki Gülcü
   */
  public class MultiplyAction extends Action {
  
    public void begin(InterpretationContext ic, String name, Attributes attributes) {
      int first = fetchInteger(ic);
      int second = fetchInteger(ic);
      ic.pushObject(new Integer(first * second));
    }
  
    /**
     * Pop the Integer object at the top of the stack. This code illustrates usage
     * of Joran's error handling paradigm.
     */
    int fetchInteger(InterpretationContext ic) {
      int result = 0;
  
      try {
        Object o1 = ic.popObject();
  
        if (o1 instanceof Integer) {
          result = ((Integer) o1).intValue();
        } else {
          String errMsg = "Object [" + o1
              + "] currently at the top of the stack is not an integer.";
          ic.addError(errMsg);
          throw new IllegalArgumentException(errMsg);
        }
      } catch (EmptyStackException ese) {
        ic.addError("Expecting an integer on the execution stack.");
        throw ese;
      }
      return result;
    }
  
    public void end(InterpretationContext ic, String name) {
      // Nothing to do here.
    }
  }