/*
 * 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.test.jndi;

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

import javax.naming.InitialContext;
import javax.naming.NamingException;

/**
 * Proxy factory that can provide contextual references to objects retrieved
 * from JNDI.
 * 
 * NOTE: This class is probably better suited as a production class, not a test support class. 
 * It needs to find a new home in a Java EE production utilities library. 
 * 
 * @param T
 *            Interface to proxy.
 * @author Erik Brakkee
 * 
 */
public class JndiProxyFactory<T> {
    /**
     * Exception thrown in case an object cannot be retrieved from JNDI. 
     * 
     * @author Erik Brakkee
     */
    public static class JndiWiringException extends RuntimeException {
        public JndiWiringException(String aMsg, Throwable aCause) {
            super(aMsg, aCause);
        }

        public JndiWiringException(String aMsg) {
            super(aMsg);
        }
    }

    /**
     * Invocation handler that does a lookup in JNDI and invokes the method on the 
     * object it found. 
     * 
     * @author Erik Brakkee
     */
    private class JndiInvocationHandler implements InvocationHandler {

        @Override
        /**
         * @throws JndiWiringException in case the object could not be retrieved from JNDI. 
         */
        public Object invoke(Object aProxy, Method aMethod, Object[] aArgs)
            throws Throwable {
            Object svcObj = null;
            try {
                InitialContext ctx = new InitialContext();
                svcObj = ctx.lookup(jndi);
            } catch (NamingException e) {
                throw new JndiWiringException(
                    "Error looking up object in JNDI at '" + jndi + "'", e);
            }
            if (svcObj == null) {
                throw new JndiWiringException("Object at '" + jndi +
                    "' is null");
            }
            if (!clazz.isInstance(svcObj)) {
                throw new JndiWiringException("Object in JNDI tree at '" +
                    jndi + "' not of type " + clazz.getName() +
                    " but of type " + svcObj.getClass().getName());
            }
            T svc = (T) svcObj;
            try {
                return aMethod.invoke(svc, aArgs);
            } catch (InvocationTargetException e) {
                throw e.getCause();
            }
        }
    }

    private String jndi;
    private Class clazz;

    /**
     * Constructs the factory.
     * 
     * @param aClass
     *            Interface class of the service to proxy.
     * @param aJndi JNDI name of the object to lookup. 
     * 
     */
    public JndiProxyFactory(Class<T> aClass, String aJndi) {
        if (!aClass.isInterface()) {
            throw new IllegalArgumentException("Class " + aClass.getName() +
                " is not an interface");
        }
        clazz = aClass;
        jndi = aJndi; 
    }

    /**
     * Gets the proxy that delegates to the thread-specific instance set by
     * {@link #set(Object)}
     * 
     * When at runtime the proxy cannot find lookup the object in JNDI, it 
     * throws {@link JndiWiringException}. 
     * 
     * @return Proxy.
     */
    public T getProxy() {
        InvocationHandler handler = new JndiInvocationHandler();
        Class proxyClass = Proxy.getProxyClass(clazz.getClassLoader(),
            new Class[] { clazz });
        T proxy;
        try {
            proxy = (T) proxyClass.getConstructor(
                new Class[] { InvocationHandler.class }).newInstance(
                new Object[] { handler });
            return proxy;
        } catch (Exception e) {
            throw new RuntimeException("Could not create proxy for " +
                clazz.getName(), e);
        }
    }
}