# ServiceReferenceInstance.java

    /*
     * Copyright (c) 2008-2011, Rickard Öberg. All Rights Reserved.
     * Copyright (c) 2008-2013, Niclas Hedhman. All Rights Reserved.
     * Copyright (c) 2012-2014, Paul Merlin. All Rights Reserved.
     *
     * 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.qi4j.runtime.service;

    import java.lang.reflect.Method;
    import org.qi4j.api.activation.Activation;
    import org.qi4j.api.activation.ActivationEventListener;
    import org.qi4j.api.activation.ActivationException;
    import org.qi4j.api.activation.PassivationException;
    import org.qi4j.api.composite.CompositeDescriptor;
    import org.qi4j.api.composite.CompositeInstance;
    import org.qi4j.api.property.StateHolder;
    import org.qi4j.api.service.ServiceDescriptor;
    import org.qi4j.api.service.ServiceImporterException;
    import org.qi4j.api.service.ServiceReference;
    import org.qi4j.api.service.ServiceUnavailableException;
    import org.qi4j.api.structure.Module;
    import org.qi4j.runtime.activation.ActivationDelegate;
    import org.qi4j.runtime.structure.ModuleInstance;

    /**
     * Implementation of ServiceReference.
     * <p>
     * This manages the actual instance of the service and implements the service Activation.
     * </p>
     * <p>
     * Whenever the service is requested a proxy is returned which points to this class. This means
     * that the instance can be passivated even though a client is holding on to a service proxy.
     * </p>
     * @param <T> Service Type
     */
    public final class ServiceReferenceInstance<T>
        implements ServiceReference<T>, Activation
    {
        private volatile ServiceInstance instance;
        private final T serviceProxy;
        private final ModuleInstance module;
        private final ServiceModel serviceModel;
        private final ActivationDelegate activation = new ActivationDelegate( this );
        private boolean active = false;

        public ServiceReferenceInstance( ServiceModel serviceModel, ModuleInstance module )
        {
            this.module = module;
            this.serviceModel = serviceModel;

            serviceProxy = newProxy();
        }

        @Override
        public String identity()
        {
            return serviceModel.identity();
        }

        @Override
        public Iterable<Class<?>> types()
        {
            return serviceModel.types();
        }

        @Override
        public <T> T metaInfo( Class<T> infoType )
        {
            return serviceModel.metaInfo( infoType );
        }

        @Override
        public synchronized T get()
        {
            return serviceProxy;
        }

        @Override
        public boolean isActive()
        {
            return active;
        }

        @Override
        public boolean isAvailable()
        {
            return getInstance().isAvailable();
        }

        public Module module()
        {
            return module;
        }

        @Override
        public void activate()
            throws ActivationException
        {
            if( serviceModel.isInstantiateOnStartup() )
            {
                getInstance();
            }
        }

        @Override
        public void passivate()
            throws PassivationException
        {
            if( instance != null )
            {
                try {
                    activation.passivate( new Runnable()
                    {
                        @Override
                        public void run()
                        {
                            active = false;
                        }
                    } );
                } finally {
                    instance = null;
                    active = false;
                }
            }
        }

        private ServiceInstance getInstance()
            throws ServiceImporterException
        {
            // DCL that works with Java 1.5 volatile semantics
            if( instance == null )
            {
                synchronized( this )
                {
                    if( instance == null )
                    {
                        instance = serviceModel.newInstance( module );

                        try
                        {
                            activation.activate( serviceModel.newActivatorsInstance( module ), instance, new Runnable()
                            {
                                @Override
                                public void run()
                                {
                                    active = true;
                                }
                            } );
                        }
                        catch( Exception e )
                        {
                            instance = null;
                            throw new ServiceUnavailableException( "Could not activate service " + serviceModel.identity(), e );
                        }
                    }
                }
            }

            return instance;
        }

        @Override
        public String toString()
        {
            return serviceModel.identity() + "(active=" + isActive() + ",module='" + module.name() + "')";
        }

        @SuppressWarnings( "unchecked" )
        public T newProxy()
        {
            return (T) serviceModel.newProxy( new ServiceReferenceInstance.ServiceInvocationHandler() );
        }

        public ServiceDescriptor serviceDescriptor()
        {
            return serviceModel;
        }

        public final class ServiceInvocationHandler
            implements CompositeInstance
        {
            @Override
            @SuppressWarnings( "unchecked" )
            public <T> T proxy()
            {
                return (T) ServiceReferenceInstance.this.get();
            }

            @Override
            public <T> T newProxy( Class<T> mixinType )
                throws IllegalArgumentException
            {
                return getInstance().newProxy( mixinType );
            }

            @Override
            public <T> T metaInfo( Class<T> infoType )
            {
                return ServiceReferenceInstance.this.metaInfo( infoType );
            }

            @Override
            public Iterable<Class<?>> types()
            {
                return ServiceReferenceInstance.this.types();
            }

            @Override
            public CompositeDescriptor descriptor()
            {
                return ServiceReferenceInstance.this.serviceDescriptor();
            }

            @Override
            public Object invokeComposite( Method method, Object[] args )
                throws Throwable
            {
                return getInstance().invokeComposite( method, args );
            }

            @Override
            public StateHolder state()
            {
                return getInstance().state();
            }

            @Override
            public Object invoke( Object object, Method method, Object[] objects )
                throws Throwable
            {
                if( method.getDeclaringClass().equals( Object.class ) )
                {
                    switch( method.getName() )
                    {
                        case "toString":
                            return serviceModel.toString();
                        case "equals":
                            return objects[0] == object;
                        case "hashCode":
                            return serviceModel.toString().hashCode();
                    }
                }

                ServiceInstance instance = getInstance();

    /*
                if (!instance.isAvailable())
                {
                    throw new ServiceUnavailableException("Service is currently not available");
                }

    */
                return instance.invoke( object, method, objects );
            }

            @Override
            public String toString()
            {
                return serviceModel.toString();
            }

            @Override
            public Module module()
            {
                return module;
            }
        }

        @Override
        public void registerActivationEventListener( ActivationEventListener listener )
        {
            activation.registerActivationEventListener( listener );
        }

        @Override
        public void deregisterActivationEventListener( ActivationEventListener listener )
        {
            activation.deregisterActivationEventListener( listener );
        }

        @Override
        public int hashCode()
        {
            return identity().hashCode();
        }

        @Override
        @SuppressWarnings( "raw" )
        public boolean equals( Object obj )
        {
            if ( obj == null ) {
                return false;
            }
            if ( getClass() != obj.getClass() ) {
                return false;
            }
            final ServiceReference other = ( ServiceReference ) obj;
            return identity().equals( other.identity() );
        }

    }