/*
 * Copyright 2005-2010 the original author or authors.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.wamblee.general;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;

/**
 * <p>
 * Serializable proxy factory that allows to create serializable proxies to
 * objects that are themselves not serializable.
 * </p>
 * 
 * <p>
 * This class does not do any cleanup so it is recommended to only use this in
 * test utilities.
 * </p>
 * 
 * 
 * @author Erik Brakkee
 * 
 * @param <T>
 */
public class SerializableProxyFactory<T> {

    private T svc;
    private Class clazz;
    private T proxy;

    /**
     * Constructs the factory.
     * 
     * @param aClass
     *            Interface class of the service to proxy.
     */
    public SerializableProxyFactory(Class<T> aClass) {
        this(aClass, null);
    }

    /**
     * Constructs the factory with a callback to create thread-specific objects
     * automatically.
     * 
     * @param aClass
     *            Interface class of the service to proxy.
     * @param aCallback
     *            Callback to create the object if it does not exist. When null,
     *            then no initialization is done.
     */
    public SerializableProxyFactory(Class<T> aClass, T aSvc) {
        if (!aClass.isInterface()) {
            throw new IllegalArgumentException("Class " + aClass.getName() +
                " is not an interface");
        }
        if (!aClass.isInstance(aSvc)) {
            throw new IllegalArgumentException("Object " + aSvc +
                " cannot be cast to " + aSvc.getClass());
        }
        svc = aSvc;
        clazz = aClass;
        proxy = createProxy();

    }

    /**
     * Gets the underlying service.
     * 
     * @return Service.
     */
    public T get() {
        return svc;
    }

    /**
     * Gets the proxy that delegates to the thread-specific instance set by
     * {@link #set(Object)}
     * 
     * @return Proxy.
     */
    public T getProxy() {
        return proxy;
    }

    private T createProxy() {
        InvocationHandler handler = new SerializableInvocationHandler(svc,
            clazz);
        Class proxyClass = Proxy.getProxyClass(clazz.getClassLoader(),
            new Class[] { clazz });
        T proxyObj;
        try {
            proxyObj = (T) proxyClass.getConstructor(
                new Class[] { InvocationHandler.class }).newInstance(
                new Object[] { handler });
            return proxyObj;
        } catch (Exception e) {
            throw new RuntimeException("Could not create proxy for " +
                clazz.getName(), e);
        }
    }
}