/*
 * Copyright 2002-2014 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.springframework.orm.jpa;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Query;
import javax.persistence.TransactionRequiredException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.util.ClassUtils;
import org.springframework.util.CollectionUtils;

/**
 * Delegate for creating a shareable JPA {@link javax.persistence.EntityManager}
 * reference for a given {@link javax.persistence.EntityManagerFactory}.
 *
 * <p>A shared EntityManager will behave just like an EntityManager fetched from
 * an application server's JNDI environment, as defined by the JPA specification.
 * It will delegate all calls to the current transactional EntityManager, if any;
 * otherwise it will fall back to a newly created EntityManager per operation.
 *
 * <p>For a behavioral definition of such a shared transactional EntityManager,
 * see {@link javax.persistence.PersistenceContextType#TRANSACTION} and its
 * discussion in the JPA spec document. This is also the default being used
 * for the annotation-based {@link javax.persistence.PersistenceContext#type()}.
 *
 * @author Juergen Hoeller
 * @author Rod Johnson
 * @author Oliver Gierke
 * @since 2.0
 * @see javax.persistence.PersistenceContext
 * @see javax.persistence.PersistenceContextType#TRANSACTION
 * @see org.springframework.orm.jpa.JpaTransactionManager
 * @see ExtendedEntityManagerCreator
 */
public abstract class SharedEntityManagerCreator {

	private static final Class<?>[] NO_ENTITY_MANAGER_INTERFACES = new Class<?>[0];

	private static final Set<String> transactionRequiringMethods = new HashSet<String>(6);

	private static final Set<String> queryTerminationMethods = new HashSet<String>(3);

	static {
		transactionRequiringMethods.add("joinTransaction");
		transactionRequiringMethods.add("flush");
		transactionRequiringMethods.add("persist");
		transactionRequiringMethods.add("merge");
		transactionRequiringMethods.add("remove");
		transactionRequiringMethods.add("refresh");

		queryTerminationMethods.add("getResultList");
		queryTerminationMethods.add("getSingleResult");
		queryTerminationMethods.add("executeUpdate");
	}


	/**
	 * Create a transactional EntityManager proxy for the given EntityManagerFactory.
	 * @param emf the EntityManagerFactory to delegate to.
	 * @return a shareable transaction EntityManager proxy
	 */
	public static EntityManager createSharedEntityManager(EntityManagerFactory emf) {
		return createSharedEntityManager(emf, null, true);
	}

	/**
	 * Create a transactional EntityManager proxy for the given EntityManagerFactory.
	 * @param emf the EntityManagerFactory to delegate to.
	 * @param properties the properties to be passed into the
	 * {@code createEntityManager} call (may be {@code null})
	 * @return a shareable transaction EntityManager proxy
	 */
	public static EntityManager createSharedEntityManager(EntityManagerFactory emf, Map<?, ?> properties) {
		return createSharedEntityManager(emf, properties, true);
	}

	/**
	 * Create a transactional EntityManager proxy for the given EntityManagerFactory.
	 * @param emf the EntityManagerFactory to delegate to.
	 * @param properties the properties to be passed into the
	 * {@code createEntityManager} call (may be {@code null})
	 * @param synchronizedWithTransaction whether to automatically join ongoing
	 * transactions (according to the JPA 2.1 SynchronizationType rules)
	 * @return a shareable transaction EntityManager proxy
	 * @since 4.0
	 */
	public static EntityManager createSharedEntityManager(
			EntityManagerFactory emf, Map<?, ?> properties, boolean synchronizedWithTransaction) {
		Class<?> entityManagerInterface = (emf instanceof EntityManagerFactoryInfo ?
				((EntityManagerFactoryInfo) emf).getEntityManagerInterface() : EntityManager.class);
		return createSharedEntityManager(emf, properties, synchronizedWithTransaction,
				(entityManagerInterface == null ? NO_ENTITY_MANAGER_INTERFACES :
					new Class<?>[] { entityManagerInterface }));
	}

	/**
	 * Create a transactional EntityManager proxy for the given EntityManagerFactory.
	 * @param emf EntityManagerFactory to obtain EntityManagers from as needed
	 * @param properties the properties to be passed into the
	 * {@code createEntityManager} call (may be {@code null})
	 * @param entityManagerInterfaces the interfaces to be implemented by the
	 * EntityManager. Allows the addition or specification of proprietary interfaces.
	 * @return a shareable transactional EntityManager proxy
	 */
	public static EntityManager createSharedEntityManager(
			EntityManagerFactory emf, Map<?, ?> properties, Class<?>... entityManagerInterfaces) {

		return createSharedEntityManager(emf, properties, true, entityManagerInterfaces);
	}

	/**
	 * Create a transactional EntityManager proxy for the given EntityManagerFactory.
	 * @param emf EntityManagerFactory to obtain EntityManagers from as needed
	 * @param properties the properties to be passed into the
	 * {@code createEntityManager} call (may be {@code null})
	 * @param synchronizedWithTransaction whether to automatically join ongoing
	 * transactions (according to the JPA 2.1 SynchronizationType rules)
	 * @param entityManagerInterfaces the interfaces to be implemented by the
	 * EntityManager. Allows the addition or specification of proprietary interfaces.
	 * @return a shareable transactional EntityManager proxy
	 * @since 4.0
	 */
	public static EntityManager createSharedEntityManager(EntityManagerFactory emf, Map<?, ?> properties,
			boolean synchronizedWithTransaction, Class<?>... entityManagerInterfaces) {

		ClassLoader cl = null;
		if (emf instanceof EntityManagerFactoryInfo) {
			cl = ((EntityManagerFactoryInfo) emf).getBeanClassLoader();
		}
		Class<?>[] ifcs = new Class<?>[entityManagerInterfaces.length + 1];
		System.arraycopy(entityManagerInterfaces, 0, ifcs, 0, entityManagerInterfaces.length);
		ifcs[entityManagerInterfaces.length] = EntityManagerProxy.class;
		return (EntityManager) Proxy.newProxyInstance(
				(cl != null ? cl : SharedEntityManagerCreator.class.getClassLoader()),
				ifcs, new SharedEntityManagerInvocationHandler(emf, properties, synchronizedWithTransaction));
	}


	/**
	 * Invocation handler that delegates all calls to the current
	 * transactional EntityManager, if any; else, it will fall back
	 * to a newly created EntityManager per operation.
	 */
	@SuppressWarnings("serial")
	private static class SharedEntityManagerInvocationHandler implements InvocationHandler, Serializable {

		private final Log logger = LogFactory.getLog(getClass());

		private final EntityManagerFactory targetFactory;

		private final Map<?, ?> properties;

		private final boolean synchronizedWithTransaction;

		private transient volatile ClassLoader proxyClassLoader;

		public SharedEntityManagerInvocationHandler(
				EntityManagerFactory target, Map<?, ?> properties, boolean synchronizedWithTransaction) {
			this.targetFactory = target;
			this.properties = properties;
			this.synchronizedWithTransaction = synchronizedWithTransaction;
			initProxyClassLoader();
		}

		private void initProxyClassLoader() {
			if (this.targetFactory instanceof EntityManagerFactoryInfo) {
				this.proxyClassLoader = ((EntityManagerFactoryInfo) this.targetFactory).getBeanClassLoader();
			}
			else {
				this.proxyClassLoader = this.targetFactory.getClass().getClassLoader();
			}
		}

		@Override
		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
			// Invocation on EntityManager interface coming in...

			if (method.getName().equals("equals")) {
				// Only consider equal when proxies are identical.
				return (proxy == args[0]);
			}
			else if (method.getName().equals("hashCode")) {
				// Use hashCode of EntityManager proxy.
				return hashCode();
			}
			else if (method.getName().equals("toString")) {
				// Deliver toString without touching a target EntityManager.
				return "Shared EntityManager proxy for target factory [" + this.targetFactory + "]";
			}
			else if (method.getName().equals("getEntityManagerFactory")) {
				// JPA 2.0: return EntityManagerFactory without creating an EntityManager.
				return this.targetFactory;
			}
			else if (method.getName().equals("getCriteriaBuilder") || method.getName().equals("getMetamodel")) {
				// JPA 2.0: return EntityManagerFactory's CriteriaBuilder/Metamodel (avoid creation of EntityManager)
				try {
					return EntityManagerFactory.class.getMethod(method.getName()).invoke(this.targetFactory);
				}
				catch (InvocationTargetException ex) {
					throw ex.getTargetException();
				}
			}
			else if (method.getName().equals("unwrap")) {
				// JPA 2.0: handle unwrap method - could be a proxy match.
				Class<?> targetClass = (Class<?>) args[0];
				if (targetClass == null || targetClass.isInstance(proxy)) {
					return proxy;
				}
			}
			else if (method.getName().equals("isOpen")) {
				// Handle isOpen method: always return true.
				return true;
			}
			else if (method.getName().equals("close")) {
				// Handle close method: suppress, not valid.
				return null;
			}
			else if (method.getName().equals("getTransaction")) {
				throw new IllegalStateException(
						"Not allowed to create transaction on shared EntityManager - " +
						"use Spring transactions or EJB CMT instead");
			}

			// Determine current EntityManager: either the transactional one
			// managed by the factory or a temporary one for the given invocation.
			EntityManager target = EntityManagerFactoryUtils.doGetTransactionalEntityManager(
					this.targetFactory, this.properties, this.synchronizedWithTransaction);

			if (method.getName().equals("getTargetEntityManager")) {
				// Handle EntityManagerProxy interface.
				if (target == null) {
					throw new IllegalStateException("No transactional EntityManager available");
				}
				return target;
			}
			else if (method.getName().equals("unwrap")) {
				// We need a transactional target now.
				if (target == null) {
					throw new IllegalStateException("No transactional EntityManager available");
				}
				// Still perform unwrap call on target EntityManager.
			}
			else if (transactionRequiringMethods.contains(method.getName())) {
				// We need a transactional target now, according to the JPA spec.
				// Otherwise, the operation would get accepted but remain unflushed...
				if (target == null) {
					throw new TransactionRequiredException("No transactional EntityManager available");
				}
			}

			// Regular EntityManager operations.
			boolean isNewEm = false;
			if (target == null) {
				logger.debug("Creating new EntityManager for shared EntityManager invocation");
				target = (!CollectionUtils.isEmpty(this.properties) ?
						this.targetFactory.createEntityManager(this.properties) :
						this.targetFactory.createEntityManager());
				isNewEm = true;
			}

			// Invoke method on current EntityManager.
			try {
				Object result = method.invoke(target, args);
				if (result instanceof Query) {
					Query query = (Query) result;
					if (isNewEm) {
						Class<?>[] ifcs = ClassUtils.getAllInterfacesForClass(query.getClass(), this.proxyClassLoader);
						result = Proxy.newProxyInstance(this.proxyClassLoader, ifcs,
								new DeferredQueryInvocationHandler(query, target));
						isNewEm = false;
					}
					else {
						EntityManagerFactoryUtils.applyTransactionTimeout(query, this.targetFactory);
					}
				}
				return result;
			}
			catch (InvocationTargetException ex) {
				throw ex.getTargetException();
			}
			finally {
				if (isNewEm) {
					EntityManagerFactoryUtils.closeEntityManager(target);
				}
			}
		}

		private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
			// Rely on default serialization, just initialize state after deserialization.
			ois.defaultReadObject();
			// Initialize transient fields.
			initProxyClassLoader();
		}
	}


	/**
	 * Invocation handler that handles deferred Query objects created by
	 * non-transactional createQuery invocations on a shared EntityManager.
	 */
	private static class DeferredQueryInvocationHandler implements InvocationHandler {

		private final Query target;

		private EntityManager em;

		public DeferredQueryInvocationHandler(Query target, EntityManager em) {
			this.target = target;
			this.em = em;
		}

		@Override
		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
			// Invocation on Query interface coming in...

			if (method.getName().equals("equals")) {
				// Only consider equal when proxies are identical.
				return (proxy == args[0]);
			}
			else if (method.getName().equals("hashCode")) {
				// Use hashCode of EntityManager proxy.
				return hashCode();
			}
			else if (method.getName().equals("unwrap")) {
				// Handle JPA 2.0 unwrap method - could be a proxy match.
				Class<?> targetClass = (Class<?>) args[0];
				if (targetClass == null || targetClass.isInstance(proxy)) {
					return proxy;
				}
			}

			// Invoke method on actual Query object.
			try {
				Object retVal = method.invoke(this.target, args);
				return (retVal == this.target ? proxy : retVal);
			}
			catch (InvocationTargetException ex) {
				throw ex.getTargetException();
			}
			finally {
				if (queryTerminationMethods.contains(method.getName())) {
					// Actual execution of the query: close the EntityManager right
					// afterwards, since that was the only reason we kept it open.
					EntityManagerFactoryUtils.closeEntityManager(this.em);
					this.em = null;
				}
			}
		}

		@Override
		protected void finalize() {
			// Trigger explicit EntityManager.close() call on garbage collection,
			// in particular for open/close statistics to be in sync. This is
			// only relevant if the Query object has not been executed, e.g.
			// when just used for the early validation of query definitions.
			EntityManagerFactoryUtils.closeEntityManager(this.em);
		}
	}

}
