/*
 * Copyright 2002-2018 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
 *
 *      https://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.transaction.support.TransactionSynchronizationManager;
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>(8);

        private static final Set<String> queryTerminatingMethods = new HashSet<String>(8);

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

                queryTerminatingMethods.add("execute");  // JPA 2.1 StoredProcedureQuery
                queryTerminatingMethods.add("executeUpdate");
                queryTerminatingMethods.add("getSingleResult");
                queryTerminatingMethods.add("getResultList");
                queryTerminatingMethods.add("getResultStream");
        }


        /**
         * 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<?> emIfc = (emf instanceof EntityManagerFactoryInfo ?
                                ((EntityManagerFactoryInfo) emf).getEntityManagerInterface() : EntityManager.class);
                return createSharedEntityManager(emf, properties, synchronizedWithTransaction,
                                (emIfc == null ? NO_ENTITY_MANAGER_INTERFACES : new Class<?>[] {emIfc}));
        }

        /**
         * Create a transactional EntityManager proxy for the given EntityManagerFactory.
         * @param emf the 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 the 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")) {
                                Class<?> targetClass = (Class<?>) args[0];
                                if (targetClass == null) {
                                        return (target != null ? target : proxy);
                                }
                                // 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 || (!TransactionSynchronizationManager.isActualTransactionActive() &&
                                                !target.getTransaction().isActive())) {
                                        throw new TransactionRequiredException("No EntityManager with actual transaction available " +
                                                        "for current thread - cannot reliably process '" + method.getName() + "' call");
                                }
                        }

                        // 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 entityManager;

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

                @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) {
                                        return this.target;
                                }
                                else if (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 (queryTerminatingMethods.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.entityManager);
                                        this.entityManager = null;
                                }
                        }
                }
        }

}