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/**
 * ModuleManager
 * Copyright (C) 2016  ThorstenMarx ([email protected])
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 com.thorstenmarx.modules.api;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.CopyOnWriteArrayList;

/**
 *
 * @author thmarx
 */
public final class ServiceRegistry {

	private final JdkCopyOnWriteArrayListMultiMap services = new JdkCopyOnWriteArrayListMultiMap<>();

	protected ServiceRegistry() {
	}

	/**
	 * Registers a new sevice implementation.
	 *
	 * @param  The service type.
	 * @param clazz The service interface.
	 * @param object The service implementation.
	 */
	public  void register(Class clazz, T object) {
		services.put(clazz.getCanonicalName(), object);
	}

	/**
	 * Removes a service implementation.
	 *
	 * @param  The service type.
	 * @param clazz The service class.
	 * @param object The service.
	 */
	public  void unregister(Class clazz, T object) {
		services.remove(clazz.getCanonicalName(), object);
	}
	/**
	 * Check if a service for the interface is registered.
	 * 
	 * @param clazz The desired service interface.
	 * @return 
	 */
	public boolean exits(Class clazz) {
		return services.exists(clazz.getCanonicalName());
	}

	/**
	 * Returns the first registered service instance of null.
	 * 
	 * @param  The service type
	 * @param clazz the service interface
	 * @return the first registered implementation or null.
	 */
	public  Optional single(Class clazz) {

		T service = null;
		if (services.exists(clazz.getCanonicalName())) {
			List value = services.get(clazz.getCanonicalName());
			ServiceInvocationHandler handler = new ServiceInvocationHandler(value.get(0));
			Object serviceInstance = Proxy.newProxyInstance(clazz.getClassLoader(), new Class[]{clazz}, handler);
			service = (T) serviceInstance;
		}

		return Optional.ofNullable(service);
	}

	/**
	 * Returns all implementations of the desired service.
	 * @param  The service type.
	 * @param clazz The service interface
	 * @return A list with all service implementations. If no implementation is registered, an empty list is returned.
	 */
	public  List get(Class clazz) {

		List result = new ArrayList<>();
		if (services.exists(clazz.getCanonicalName())) {
			for (Object value : services.get(clazz.getCanonicalName())) {
				ServiceInvocationHandler handler = new ServiceInvocationHandler(value);
				Object serviceInstance = Proxy.newProxyInstance(clazz.getClassLoader(), new Class[]{clazz}, handler);
				result.add((T) serviceInstance);
			}
		}

		return result;
	}

	private static class ServiceInvocationHandler implements InvocationHandler {

		final Object service;

		public ServiceInvocationHandler(final Object service) {
			this.service = service;
		}

		@Override
		public Object invoke(Object o, Method method, Object[] os) throws Throwable {

			Method m = service.getClass().getMethod(method.getName(), method.getParameterTypes());
			return m.invoke(service, os);
		}

	}

	private class JdkCopyOnWriteArrayListMultiMap {

		private final ConcurrentMap> cache = new ConcurrentHashMap<>();

		public boolean exists(K k) {
			return cache.containsKey(k);
		}

		public List get(K k) {
			return cache.get(k);
		}

		public List remove(K k) {
			return cache.remove(k);
		}

		public void put(K k, V v) {
			List list = cache.get(k);
			if (list == null) {
				list = new CopyOnWriteArrayList<>();
				List oldList = cache.putIfAbsent(k, list);
				if (oldList != null) {
					list = oldList;
				}
			}
			list.add(v);
		}

		public boolean remove(K k, V v) {
			List list = cache.get(k);
			if (list == null) {
				return false;
			}
			if (list.isEmpty()) {
				cache.remove(k);
				return false;
			}
			boolean removed = list.remove(v);
			if (removed && list.isEmpty()) {
				cache.remove(k);
			}
			return removed;
		}
	}
}
    

    

    
            
    
            







    
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