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Contains common utility code, reusable outside Hudson.
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/*******************************************************************************
 *
 * Copyright (c) 2010-2011 Sonatype, Inc.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors: 
 *
 *   
 *     
 *
 *******************************************************************************/ 

package org.hudsonci.utils.event;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * Support for {@link EventHandler} implementations.
 *
 * @author Jason Dillon
 * @since 2.1.0
 */
public abstract class EventHandlerSupport
    implements EventHandler
{
    protected final Logger log = LoggerFactory.getLogger(getClass());

    private ContextType context;

    private Class eventType;

    public void init(final ContextType context) {
        this.context = checkNotNull( context );
    }

    protected ContextType getContext() {
        return context;
    }

    /**
     * Accepts the event if it is a compatible type; determined by {@link #getEventType}.
     */
    public boolean accept(final Object event) {
        checkNotNull( event );
        return getEventType().isAssignableFrom(event.getClass());
    }

    /**
     * Determines the event type of the handler.
     */
    protected Class getEventType() {
        if (eventType == null) {
            // find public void handle(Object) method
            for (Method method : getClass().getDeclaredMethods()) {
                if (Modifier.isPublic(method.getModifiers()) &&
                    method.getReturnType() == Void.TYPE &&
                    method.getName().equals("handle") &&
                    method.getParameterTypes().length == 1 &&
                    // Ignore methods with Object as param, generics muck puts this in here and matches when we want the specific typed method
                    method.getParameterTypes()[0] != Object.class)
                {
                    eventType = method.getParameterTypes()[0];
                    log.debug("Determined type: {}, from method: {}", eventType.getName(), method);
                    break;
                }
            }

            if (eventType == null) {
                throw new Error(getClass().getName() + " missing 'public void handle()' method");
            }
        }

        return eventType;
    }
}