/**
 * 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 java.util.EmptyStackException;

import org.xml.sax.Attributes;

import ch.qos.logback.core.joran.action.Action;
import ch.qos.logback.core.joran.spi.InterpretationContext;


/**
 * This action adds the two integers at the top of the stack (they are removed)
 * and pushes the result to the top the stack.  
 * 
 * @author Ceki G&uuml;lc&uuml;
 */
public class AddAction extends Action {
  
  public void begin(InterpretationContext ic, String name, Attributes attributes) {
    int first = fetchInteger(ic);
    int second = fetchInteger(ic);
    // Push the result of the addition for the following actions.
    ic.pushObject(new Integer(first + second));
  }

  /**
   * Pop the Integer object at the top of the stack.
   * This code also  illustrates usage of Joran's error handling paradigm. 
   */
  int fetchInteger(InterpretationContext ic) {
    int result = 0;

    try {
      // Pop the object at the top of the interpretation context's stack.
      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.
  }
}
