package org.wamblee.support.persistence;

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

import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;
import javax.sql.DataSource;

import org.wamblee.support.jndi.StubInitialContextFactory;

/**
 * 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 {

    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 em
         *            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 em);
    }

    private PersistenceUnitDescription persistenceUnit;
    private DataSource dataSource;
    private EntityManagerFactory factory;

    /**
     * Constructs the builder.
     * 
     * @param aDataSource
     *            Datasource of database.
     * @param aPersistenceUnit
     *            Persistence unit.
     */
    public JpaBuilder(DataSource aDataSource,
        PersistenceUnitDescription aPersistenceUnit) {
        persistenceUnit = aPersistenceUnit;
        dataSource = aDataSource;
        StubInitialContextFactory.register();
    }

    /**
     * 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 {
        try {
            InitialContext ctx = new InitialContext();
            ctx.bind(persistenceUnit.getJndiName(), dataSource);
        } catch (NamingException e) {
            throw new RuntimeException("JNDI problem", e);
        }
        factory = createFactory();
        execute(new JpaUnitOfWork<Void>() {
            public Void execute(EntityManager em) {
                // Empty, just to trigger database schema creation.
                return null;
            }
        });
    }

    /**
     * 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>();

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

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

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

    /**
     * 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 = factory.createEntityManager();
        EntityTransaction transaction = em.getTransaction();
        transaction.begin();
        try {
            T value = aWork.execute(em);
            transaction.commit();
            return value;
        } catch (Exception e) {
            LOGGER.log(Level.WARNING, "Exception occured", e);
            transaction.rollback();
            throw e;
        } finally {
            em.close();
        }
    }
}