/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2010, Red Hat Inc. or third-party contributors as
 * indicated by the @author tags or express copyright attribution
 * statements applied by the authors.  All third-party contributions are
 * distributed under license by Red Hat Inc.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.hibernate.boot.registry.classloading.internal;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.ServiceLoader;

import org.hibernate.boot.registry.classloading.spi.ClassLoaderService;
import org.hibernate.boot.registry.classloading.spi.ClassLoadingException;
import org.hibernate.cfg.AvailableSettings;
import org.hibernate.internal.CoreLogging;
import org.hibernate.internal.util.ClassLoaderHelper;
import org.hibernate.internal.util.config.ConfigurationHelper;

import org.jboss.logging.Logger;

Standard implementation of the service for interacting with class loaders
Author:
Steve Ebersole/**
 * Standard implementation of the service for interacting with class loaders
 *
 * @author Steve Ebersole
 */
public class ClassLoaderServiceImpl implements ClassLoaderService {
	private static final Logger log = CoreLogging.logger( ClassLoaderServiceImpl.class );

	private final Map<Class, ServiceLoader> serviceLoaders = new HashMap<Class, ServiceLoader>();
	private AggregatedClassLoader aggregatedClassLoader;

	
Constructs a ClassLoaderServiceImpl with standard set-up
/**
	 * Constructs a ClassLoaderServiceImpl with standard set-up
	 */
	public ClassLoaderServiceImpl() {
		this( ClassLoaderServiceImpl.class.getClassLoader() );
	}

	
Constructs a ClassLoaderServiceImpl with the given ClassLoader
Params:
classLoader – The ClassLoader to use/**
	 * Constructs a ClassLoaderServiceImpl with the given ClassLoader
	 *
	 * @param classLoader The ClassLoader to use
	 */
	public ClassLoaderServiceImpl(ClassLoader classLoader) {
		this( Collections.singletonList( classLoader ) );
	}

	
Constructs a ClassLoaderServiceImpl with the given ClassLoader instances
Params:
providedClassLoaders – The ClassLoader instances to use/**
	 * Constructs a ClassLoaderServiceImpl with the given ClassLoader instances
	 *
	 * @param providedClassLoaders The ClassLoader instances to use
	 */
	public ClassLoaderServiceImpl(Collection<ClassLoader> providedClassLoaders) {
		final LinkedHashSet<ClassLoader> orderedClassLoaderSet = new LinkedHashSet<ClassLoader>();

		// first, add all provided class loaders, if any
		if ( providedClassLoaders != null ) {
			for ( ClassLoader classLoader : providedClassLoaders ) {
				if ( classLoader != null ) {
					orderedClassLoaderSet.add( classLoader );
				}
			}
		}

		// normalize adding known class-loaders...
		// then the Hibernate class loader
		orderedClassLoaderSet.add( ClassLoaderServiceImpl.class.getClassLoader() );

		// then the TCCL, if one...
		final ClassLoader tccl = locateTCCL();
		if ( tccl != null ) {
			orderedClassLoaderSet.add( tccl );
		}
		// finally the system classloader
		final ClassLoader sysClassLoader = locateSystemClassLoader();
		if ( sysClassLoader != null ) {
			orderedClassLoaderSet.add( sysClassLoader );
		}

		// now build the aggregated class loader...
		this.aggregatedClassLoader = new AggregatedClassLoader( orderedClassLoaderSet );
	}

	
No longer used/supported!
Params:
configValues – The config values
Returns:
The built service
Deprecated:
No longer used/supported!/**
	 * No longer used/supported!
	 *
	 * @param configValues The config values
	 *
	 * @return The built service
	 *
	 * @deprecated No longer used/supported!
	 */
	@Deprecated
	@SuppressWarnings({"UnusedDeclaration", "unchecked", "deprecation"})
	public static ClassLoaderServiceImpl fromConfigSettings(Map configValues) {
		final List<ClassLoader> providedClassLoaders = new ArrayList<ClassLoader>();

		final Collection<ClassLoader> classLoaders = (Collection<ClassLoader>) configValues.get( AvailableSettings.CLASSLOADERS );
		if ( classLoaders != null ) {
			for ( ClassLoader classLoader : classLoaders ) {
				providedClassLoaders.add( classLoader );
			}
		}

		addIfSet( providedClassLoaders, AvailableSettings.APP_CLASSLOADER, configValues );
		addIfSet( providedClassLoaders, AvailableSettings.RESOURCES_CLASSLOADER, configValues );
		addIfSet( providedClassLoaders, AvailableSettings.HIBERNATE_CLASSLOADER, configValues );
		addIfSet( providedClassLoaders, AvailableSettings.ENVIRONMENT_CLASSLOADER, configValues );

		if ( providedClassLoaders.isEmpty() ) {
			log.debugf( "Incoming config yielded no classloaders; adding standard SE ones" );
			final ClassLoader tccl = locateTCCL();
			if ( tccl != null ) {
				providedClassLoaders.add( tccl );
			}
			providedClassLoaders.add( ClassLoaderServiceImpl.class.getClassLoader() );
		}

		return new ClassLoaderServiceImpl( providedClassLoaders );
	}

	private static void addIfSet(List<ClassLoader> providedClassLoaders, String name, Map configVales) {
		final ClassLoader providedClassLoader = (ClassLoader) configVales.get( name );
		if ( providedClassLoader != null ) {
			providedClassLoaders.add( providedClassLoader );
		}
	}

	private static ClassLoader locateSystemClassLoader() {
		try {
			return ClassLoader.getSystemClassLoader();
		}
		catch (Exception e) {
			return null;
		}
	}

	private static ClassLoader locateTCCL() {
		try {
			return ClassLoaderHelper.getContextClassLoader();
		}
		catch (Exception e) {
			return null;
		}
	}

	private static class AggregatedClassLoader extends ClassLoader {
		private ClassLoader[] individualClassLoaders;

		private AggregatedClassLoader(final LinkedHashSet<ClassLoader> orderedClassLoaderSet) {
			super( null );
			individualClassLoaders = orderedClassLoaderSet.toArray( new ClassLoader[orderedClassLoaderSet.size()] );
		}

		@Override
		public Enumeration<URL> getResources(String name) throws IOException {
			final LinkedHashSet<URL> resourceUrls = new LinkedHashSet<URL>();

			for ( ClassLoader classLoader : individualClassLoaders ) {
				final Enumeration<URL> urls = classLoader.getResources( name );
				while ( urls.hasMoreElements() ) {
					resourceUrls.add( urls.nextElement() );
				}
			}

			return new Enumeration<URL>() {
				final Iterator<URL> resourceUrlIterator = resourceUrls.iterator();

				@Override
				public boolean hasMoreElements() {
					return resourceUrlIterator.hasNext();
				}

				@Override
				public URL nextElement() {
					return resourceUrlIterator.next();
				}
			};
		}

		@Override
		protected URL findResource(String name) {
			for ( ClassLoader classLoader : individualClassLoaders ) {
				final URL resource = classLoader.getResource( name );
				if ( resource != null ) {
					return resource;
				}
			}
			return super.findResource( name );
		}

		@Override
		protected Class<?> findClass(String name) throws ClassNotFoundException {
			for ( ClassLoader classLoader : individualClassLoaders ) {
				try {
					return classLoader.loadClass( name );
				}
				catch (Exception ignore) {
				}
			}

			throw new ClassNotFoundException( "Could not load requested class : " + name );
		}

		public void destroy() {
			individualClassLoaders = null;
		}
	}

	@Override
	@SuppressWarnings({"unchecked"})
	public <T> Class<T> classForName(String className) {
		try {
			return (Class<T>) Class.forName( className, true, aggregatedClassLoader );
		}
		catch (Exception e) {
			throw new ClassLoadingException( "Unable to load class [" + className + "]", e );
		}
	}

	@Override
	public URL locateResource(String name) {
		// first we try name as a URL
		try {
			return new URL( name );
		}
		catch (Exception ignore) {
		}

		try {
			return aggregatedClassLoader.getResource( name );
		}
		catch (Exception ignore) {
		}

		return null;
	}

	@Override
	public InputStream locateResourceStream(String name) {
		// first we try name as a URL
		try {
			log.tracef( "trying via [new URL(\"%s\")]", name );
			return new URL( name ).openStream();
		}
		catch (Exception ignore) {
		}

		try {
			log.tracef( "trying via [ClassLoader.getResourceAsStream(\"%s\")]", name );
			final InputStream stream = aggregatedClassLoader.getResourceAsStream( name );
			if ( stream != null ) {
				return stream;
			}
		}
		catch (Exception ignore) {
		}

		final String stripped = name.startsWith( "/" ) ? name.substring( 1 ) : null;

		if ( stripped != null ) {
			try {
				log.tracef( "trying via [new URL(\"%s\")]", stripped );
				return new URL( stripped ).openStream();
			}
			catch (Exception ignore) {
			}

			try {
				log.tracef( "trying via [ClassLoader.getResourceAsStream(\"%s\")]", stripped );
				final InputStream stream = aggregatedClassLoader.getResourceAsStream( stripped );
				if ( stream != null ) {
					return stream;
				}
			}
			catch (Exception ignore) {
			}
		}

		return null;
	}

	@Override
	public List<URL> locateResources(String name) {
		final ArrayList<URL> urls = new ArrayList<URL>();
		try {
			final Enumeration<URL> urlEnumeration = aggregatedClassLoader.getResources( name );
			if ( urlEnumeration != null && urlEnumeration.hasMoreElements() ) {
				while ( urlEnumeration.hasMoreElements() ) {
					urls.add( urlEnumeration.nextElement() );
				}
			}
		}
		catch (Exception ignore) {
		}

		return urls;
	}

	@Override
	@SuppressWarnings("unchecked")
	public <S> LinkedHashSet<S> loadJavaServices(Class<S> serviceContract) {
		ServiceLoader<S> serviceLoader;
		if ( serviceLoaders.containsKey( serviceContract ) ) {
			serviceLoader = serviceLoaders.get( serviceContract );
		}
		else {
			serviceLoader = ServiceLoader.load( serviceContract, aggregatedClassLoader );
			serviceLoaders.put( serviceContract, serviceLoader );
		}

		final LinkedHashSet<S> services = new LinkedHashSet<S>();
		for ( S service : serviceLoader ) {
			services.add( service );
		}
		return services;
	}

	@Override
	public void stop() {
		for ( ServiceLoader serviceLoader : serviceLoaders.values() ) {
			serviceLoader.reload(); // clear service loader providers
		}
		serviceLoaders.clear();

		if ( aggregatedClassLoader != null ) {
			aggregatedClassLoader.destroy();
			aggregatedClassLoader = null;
		}
	}

	// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
	// completely temporary !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
	// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

	
Hack around continued (temporary) need to sometimes set the TCCL for code we call that expects it.
Type parameters:
<T> – The result type/**
	 * Hack around continued (temporary) need to sometimes set the TCCL for code we call that expects it.
	 *
	 * @param <T> The result type
	 */
	public static interface Work<T> {
		
The work to be performed with the TCCL set
Returns:
The result of the work/**
		 * The work to be performed with the TCCL set
		 *
		 * @return The result of the work
		 */
		public T perform();

		
Get the configuration values of the Work context.
Returns:
the configuration values;/**
		 * Get the configuration values of the Work context.
		 *
		 * @return the configuration values;
		 */
		public Map getConfigurationValues();
	}

	
Perform some discrete work with with the TCCL set to our aggregated ClassLoader
Params:
work – The discrete work to be done
Type parameters:
<T> – The type of the work result
Returns:
The work result./**
	 * Perform some discrete work with with the TCCL set to our aggregated ClassLoader
	 *
	 * @param work The discrete work to be done
	 * @param <T> The type of the work result
	 *
	 * @return The work result.
	 */
	public <T> T withTccl(Work<T> work) {
		final ClassLoader tccl = Thread.currentThread().getContextClassLoader();

		boolean set = false;

		/**
		 * The value for hibernate.classloading.use_current_tccl_as_parent
		 * determines whether the thread context ClassLoader for this
		 * Thread (TCCL) should use the current TCCL as parent ClassLoader.
		 * Default is true.
		 */
		final boolean useCurrentTcclAsParent = ConfigurationHelper.getBoolean(
				"hibernate.classloading.use_current_tccl_as_parent",
				work.getConfigurationValues(),
				true
		);

		try {
			final ClassLoader tcclNew;
			if ( useCurrentTcclAsParent ) {
				tcclNew = new TcclSafeAggregatedClassLoader( aggregatedClassLoader, tccl );
			}
			else {
				tcclNew = aggregatedClassLoader;
			}
			Thread.currentThread().setContextClassLoader( tcclNew );
			set = true;
		}
		catch (Exception ignore) {
		}

		try {
			return work.perform();
		}
		finally {
			if ( set ) {
				Thread.currentThread().setContextClassLoader( tccl );
			}
		}

	}

	// TODO: Remove in ORM 5!  See HHH-8818
	private class TcclSafeAggregatedClassLoader extends ClassLoader {
		private final AggregatedClassLoader aggregatedClassLoader;
		
		private TcclSafeAggregatedClassLoader(AggregatedClassLoader aggregatedClassLoader, ClassLoader tccl) {
			super(tccl);
			this.aggregatedClassLoader = aggregatedClassLoader;
		}
		
		@Override
		public Enumeration<URL> getResources(String name) throws IOException {
			return aggregatedClassLoader.getResources( name );
		}

		@Override
		protected URL findResource(String name) {
			return aggregatedClassLoader.findResource( name );
		}

		@Override
		protected Class<?> findClass(String name) throws ClassNotFoundException {
			return aggregatedClassLoader.findClass( name );
		}
	}

}