package ie.dcu.swt;

import java.io.Serializable;
import java.lang.reflect.*;
import java.util.logging.*;

import org.eclipse.swt.widgets.*;

/**
 * Dispatch simple method calls by reflection.
 * 
 * @author Kevin McGuinness
 */
public class Dispatcher implements Serializable, Listener {
	
	/**
	 * Serialization UID
	 */
	private static final long serialVersionUID = -8518627659417915880L;
	
	/**
	 * Logger used to report errors.
	 */
	private static final Logger logger = Logger.getLogger("Dispatcher");
	
	/**
	 * The target object.
	 */
	public final Object object;
	
	/**
	 * The target method.
	 */
	public final Method method;

	/**
	 * Create a dispatcher that calls the given method on the given object. The
	 * method should have no parameters. If a SecurityException or a
	 * NoSuchMethodException occurs when getting the Method object, then it is
	 * logged and wrapped in a RuntimeException and re-thrown.
	 * 
	 * @param object
	 *            The target object.
	 * @param method
	 *            The method name.
	 * @throws RuntimeException
	 *             If a SecurityException or NoSuchMethodException occurs.
	 */
	public Dispatcher(Object object, String method) 
		throws RuntimeException 
	{
		try {
			this.object = object;
			this.method = object.getClass().getMethod(method);
		} catch (SecurityException e) {
			logger.log(Level.SEVERE, "Cannot get method by reflection", e);
			throw new RuntimeException(e);
		} catch (NoSuchMethodException e) {
			logger.log(Level.SEVERE, "Method not found: " + method, e);
			throw new RuntimeException(e);
		}
	}

	/**
	 * Invoke the method on the object by reflection. If any exception occurs in
	 * the invocation, it is logged, then wrapped in a RuntimeException and
	 * re-thrown.
	 * 
	 * @return The result of the method invocation, or null if the method is
	 *         void.
	 * 
	 * @throws RuntimeException
	 *             If any exception occurs in the invocation, it is wrapped in a
	 *             RuntimeException and re-thrown.
	 */
	public Object invoke() {
		try {
			return method.invoke(object);
		} catch (IllegalArgumentException e) {
			logger.log(Level.SEVERE, "Error invoking method", e);
			throw new RuntimeException(e);
		} catch (IllegalAccessException e) {
			logger.log(Level.SEVERE, "Error invoking method", e);
			throw new RuntimeException(e);
		} catch (InvocationTargetException e) {
			logger.log(Level.WARNING, "Invocation target error", e);
			throw new RuntimeException(e);
		}
	}

	/**
	 * Allows the dispatcher to be used as an SWT listener. The event and
	 * return value are ignored.
	 */
	public void handleEvent(Event event) {
		invoke();
	}
}