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package javax.persistence;

import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.persistence.spi.LoadState;
import javax.persistence.spi.PersistenceProvider;
import javax.persistence.spi.PersistenceProviderResolver;
import javax.persistence.spi.PersistenceProviderResolverHolder;

/**
 * Bootstrap class that is used to obtain an {@link EntityManagerFactory} in Java SE environments.
 * 
 * 
 * The Persistence class is available in a Java EE container environment as well; however, support for the Java SE
 * bootstrapping APIs is not required in container environments.
 * 
 * 
 * The Persistence class is used to obtain a {@link javax.persistence.PersistenceUtil PersistenceUtil} instance in both Java EE
 * and Java SE environments.
 * 
 * @since Java Persistence 1.0
 */
public class Persistence {

	/**
	 * Implementation of PersistenceUtil interface
	 * 
	 * @since Java Persistence 2.0
	 */
	private static class PersistenceUtilImpl implements PersistenceUtil {
		@Override
		public boolean isLoaded(Object entity) {
			final PersistenceProviderResolver resolver = PersistenceProviderResolverHolder.getPersistenceProviderResolver();

			final List providers = resolver.getPersistenceProviders();

			for (final PersistenceProvider provider : providers) {
				final LoadState loadstate = provider.getProviderUtil().isLoaded(entity);
				if (loadstate == LoadState.LOADED) {
					return true;
				}
				else if (loadstate == LoadState.NOT_LOADED) {
					return false;
				} // else continue
			}
			// None of the providers could determine the load state
			return true;
		}

		@Override
		public boolean isLoaded(Object entity, String attributeName) {
			final PersistenceProviderResolver resolver = PersistenceProviderResolverHolder.getPersistenceProviderResolver();

			final List providers = resolver.getPersistenceProviders();

			for (final PersistenceProvider provider : providers) {
				final LoadState loadstate = provider.getProviderUtil().isLoadedWithoutReference(entity, attributeName);
				if (loadstate == LoadState.LOADED) {
					return true;
				}
				else if (loadstate == LoadState.NOT_LOADED) {
					return false;
				} // else continue
			}

			// None of the providers could determine the load state try isLoadedWithReference
			for (final PersistenceProvider provider : providers) {
				final LoadState loadstate = provider.getProviderUtil().isLoadedWithReference(entity, attributeName);
				if (loadstate == LoadState.LOADED) {
					return true;
				}
				else if (loadstate == LoadState.NOT_LOADED) {
					return false;
				} // else continue
			}

			// None of the providers could determine the load state.
			return true;
		}
	}

	/**
	 * This instance variable is deprecated and should be removed and is only here for TCK backward compatibility
	 * 
	 * @since Java Persistence 1.0
	 * @deprecated
	 */
	@Deprecated
	protected static final Set providers = new HashSet();

	/**
	 * Create and return an EntityManagerFactory for the named persistence unit.
	 * 
	 * @param persistenceUnitName
	 *            the name of the persistence unit
	 * @return the factory that creates EntityManagers configured according to the specified persistence unit
	 */
	public static EntityManagerFactory createEntityManagerFactory(String persistenceUnitName) {
		return Persistence.createEntityManagerFactory(persistenceUnitName, null);
	}

	/**
	 * Create and return an EntityManagerFactory for the named persistence unit using the given properties.
	 * 
	 * @param persistenceUnitName
	 *            the name of the persistence unit
	 * @param properties
	 *            Additional properties to use when creating the factory. The values of these properties override any values that may have
	 *            been configured elsewhere.
	 * @return the factory that creates EntityManagers configured according to the specified persistence unit.
	 */
	public static EntityManagerFactory createEntityManagerFactory(String persistenceUnitName, Map properties) {
		EntityManagerFactory emf = null;
		final PersistenceProviderResolver resolver = PersistenceProviderResolverHolder.getPersistenceProviderResolver();

		final List providers = resolver.getPersistenceProviders();

		for (final PersistenceProvider provider : providers) {
			emf = provider.createEntityManagerFactory(persistenceUnitName, properties);
			if (emf != null) {
				break;
			}
		}
		if (emf == null) {
			throw new PersistenceException("No Persistence provider for EntityManager named " + persistenceUnitName);
		}
		return emf;
	}

	/**
	 * Return the PersistenceUtil instance
	 * 
	 * @return PersistenceUtil instance
	 * @since Java Persistence 2.0
	 */
	public static PersistenceUtil getPersistenceUtil() {
		return new PersistenceUtilImpl();
	}
}