/*
 * 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.persistence;

import java.util.Map;
import java.util.TreeMap;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;
import javax.persistence.PersistenceException;

import org.wamblee.general.ThreadSpecificProxyFactory;
import org.wamblee.test.jndi.StubInitialContextFactory;
import org.wamblee.test.transactions.TransactionResource;

/**
 * Utility for building an appropriately configured EntityManagerFactory. The
 * idea is that a persistence.xml is used unchanged from the production version.
 * This utility will then add the additional properties required for execution
 * in a standalone environment.
 * 
 * The other purpose is to to shield dependencies of the test code on a
 * particular JPA provider.
 */
public class JpaBuilder implements TransactionResource<EntityManager> {

    private static final Logger LOGGER = Logger.getLogger(JpaBuilder.class
        .getName());

    /**
     * Callback interface to execute some JPA code within a transaction with the
     * entitymanager to use provided as input.
     */
    public static interface JpaUnitOfWork<T> {
        /**
         * Executes the unit of work. A transaction has been started.
         * 
         * @param aEm
         *            Entity manager.
         * @return Result of the execute method. If you don't want to return
         *         anything use <code>Void</code> for the return type and return
         *         null from the implementation.
         */
        T execute(EntityManager aEm) throws Exception;
    }

    private PersistenceUnitDescription persistenceUnit;
    private String url;
    private String user;
    private String password;
    private EntityManagerFactory factory;
    private ThreadSpecificProxyFactory<EntityManager> entityManager;

    /**
     * Constructs the builder.
     * 
     * @param aUrl
     *            JDBC URL
     * @param aUser
     *            User name
     * @param aPassword
     *            Password.
     * @param aPersistenceUnit
     *            Persistence unit.
     */
    public JpaBuilder(String aUrl, String aUser, String aPassword,
        PersistenceUnitDescription aPersistenceUnit) {
        persistenceUnit = aPersistenceUnit;
        url = aUrl;
        user = aUser;
        password = aPassword;
        entityManager = new ThreadSpecificProxyFactory<EntityManager>(
            EntityManager.class);
    }

    /**
     * Starts the builder, which in particular, mocks JNDI, binds the datasource
     * the JNDI where the persistence unit expects it, creates the entity
     * manager factory, and forces creation of the database schema.
     */
    public void start() throws Exception {
        factory = createFactory();
        try {
            execute(new JpaUnitOfWork<Void>() {
                public Void execute(EntityManager aEm) {
                    // Empty, just to trigger database schema creation.
                    return null;
                }
            });
        } catch (PersistenceException e) {
            factory.close();
            throw e;
        }
    }

    /**
     * Stops the entity manager factory and disables JNDI mocking.
     */
    public void stop() {
        StubInitialContextFactory.unregister();
        factory.close();
    }

    /**
     * Creates a new entity manager factory. Typically not used by test code.
     * 
     * @return Entity manager factory.
     */
    public EntityManagerFactory createFactory() {
        Map<String, String> jpaProps = new TreeMap<String, String>();

        jpaProps.put("javax.persistence.jtaDataSource", null);
        jpaProps.put("javax.persistence.transactionType", "RESOURCE_LOCAL");
        jpaProps.put("javax.persistence.jdbc.url", url);
        jpaProps.put("javax.persistence.jdbc.user", user);
        jpaProps.put("javax.persistence.jdbc.password", password);

        JpaCustomizerBuilder.getCustomizer().customize(persistenceUnit,
            jpaProps);

        // jpaProps.put("javax.persistence.provider",
        // HibernatePersistence.class.getName());
        EntityManagerFactory emf = Persistence.createEntityManagerFactory(
            persistenceUnit.getUnitName(), jpaProps);

        LOGGER.info("Using " + emf.getClass());
        return emf;
    }

    /**
     * Executes a unit of work. This creates an entitymanager and runs the
     * {@link JpaUnitOfWork#execute(EntityManager)} within a transaction,
     * passing it the entity manager. Use of this method saves a lot of typing
     * for applications.
     * 
     * @param aWork
     *            Work to execute.
     * @return The return value of the execute method of the unit of work.
     */
    public <T> T execute(JpaUnitOfWork<T> aWork) throws Exception {
        EntityManager em = begin();
        try {
            T value = aWork.execute(em);
            commit(em);
            return value;
        } catch (Exception e) {
            LOGGER.log(Level.WARNING, "Exception occured", e);
            rollback(em);
            throw e;
        }
    }

    @Override
    public EntityManager begin() {
        EntityManager em = factory.createEntityManager();
        EntityTransaction transaction = em.getTransaction();
        transaction.begin();
        entityManager.set(em);
        return em;
    }

    @Override
    public void commit(EntityManager aEntityManager) {
        try {
            aEntityManager.getTransaction().commit();
        } finally {
            aEntityManager.close();
            entityManager.set(null);
        }
    }

    @Override
    public void rollback(EntityManager aEntityManager) {
        try {
            EntityTransaction transaction = aEntityManager.getTransaction();
            if (transaction.isActive()) {
                transaction.rollback();
            }
        } finally {
            if (aEntityManager.isOpen()) {
                aEntityManager.close();
            }
            entityManager.set(null);
        }
    }

    /**
     * Gets a contextual reference to an entity manager that delegates to the
     * appropriate (current) one which is active for the current transaction.
     * 
     * @return EntityManager.
     */
    public EntityManager getContextualEntityManager() {
        return entityManager.getProxy();
    }
}