# UnitOfWorkNotificationConcern.java

    /**
     *
     * Copyright 2009-2010 Rickard Öberg AB
     *
     * 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.library.eventsourcing.domain.factory;

    import java.io.IOException;
    import org.qi4j.api.Qi4j;
    import org.qi4j.api.concern.ConcernOf;
    import org.qi4j.api.entity.EntityComposite;
    import org.qi4j.api.injection.scope.Service;
    import org.qi4j.api.injection.scope.Structure;
    import org.qi4j.api.structure.Application;
    import org.qi4j.api.unitofwork.UnitOfWork;
    import org.qi4j.api.unitofwork.UnitOfWorkCallback;
    import org.qi4j.api.unitofwork.UnitOfWorkCompletionException;
    import org.qi4j.api.unitofwork.UnitOfWorkFactory;
    import org.qi4j.api.value.ValueBuilder;
    import org.qi4j.api.value.ValueBuilderFactory;
    import org.qi4j.functional.Iterables;
    import org.qi4j.io.Inputs;
    import org.qi4j.io.Output;
    import org.qi4j.library.eventsourcing.domain.api.DomainEventValue;
    import org.qi4j.library.eventsourcing.domain.api.UnitOfWorkDomainEventsValue;
    import org.qi4j.library.eventsourcing.domain.source.EventStore;
    import org.qi4j.library.eventsourcing.domain.source.UnitOfWorkEventsVisitor;
    import org.qi4j.library.eventsourcing.domain.spi.CurrentUser;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;

    /**
     * Notify event listeners when a complete UoW of domain events is available.
     */
    public class UnitOfWorkNotificationConcern
            extends ConcernOf<DomainEventFactory>
            implements DomainEventFactory
    {
        @Service
        EventStore eventStore;

        @Service
        Iterable<UnitOfWorkEventsVisitor> transactionVisitors;

        @Service
        CurrentUser currentUser;

        @Structure
        ValueBuilderFactory vbf;

        @Structure
        UnitOfWorkFactory uowf;

        @Structure
        Qi4j api;

        String version;

        Logger logger = LoggerFactory.getLogger( DomainEventFactory.class );

        Output<UnitOfWorkDomainEventsValue, IOException> eventOutput;

        public void init( @Structure Application application )
        {
            version = application.version();
            eventOutput = eventStore.storeEvents();
        }

        @Override
        public DomainEventValue createEvent( EntityComposite entity, String name, Object[] args )
        {
            final UnitOfWork unitOfWork = uowf.currentUnitOfWork();

            DomainEventValue eventValue = next.createEvent( api.dereference( entity ), name, args );

            // Add eventValue to list in UoW
            UnitOfWorkEvents events = unitOfWork.metaInfo(UnitOfWorkEvents.class );
            if (events == null)
            {
                events = new UnitOfWorkEvents();
                unitOfWork.setMetaInfo( events );

                unitOfWork.addUnitOfWorkCallback( new UnitOfWorkCallback()
                {
                    String user;

                    @Override
                    public void beforeCompletion() throws UnitOfWorkCompletionException
                    {
                        user = currentUser.getCurrentUser();
                    }

                    @Override
                    public void afterCompletion( UnitOfWorkStatus status )
                    {
                        if (status.equals( UnitOfWorkStatus.COMPLETED ))
                        {
                            UnitOfWorkEvents events = unitOfWork.metaInfo( UnitOfWorkEvents.class );

                            ValueBuilder<UnitOfWorkDomainEventsValue> builder = vbf.newValueBuilder( UnitOfWorkDomainEventsValue.class );
                            builder.prototype().user().set( user );
                            builder.prototype().timestamp().set( System.currentTimeMillis() );
                            builder.prototype().usecase().set( unitOfWork.usecase().name() );
                            builder.prototype().version().set( version );
                            builder.prototype().events().get().addAll( events.getEventValues() );

                            try
                            {
                                final UnitOfWorkDomainEventsValue unitOfWorkDomainValue = builder.newInstance();
                                Inputs.iterable( Iterables.iterable( unitOfWorkDomainValue ) ).transferTo( eventOutput );

                                for (UnitOfWorkEventsVisitor unitOfWorkEventsVisitor : transactionVisitors)
                                {
                                    try
                                    {
                                        unitOfWorkEventsVisitor.visit( unitOfWorkDomainValue );
                                    } catch (Exception e)
                                    {
                                        logger.warn( "Could not deliver events", e );

                                    }
                                }
                            } catch (IOException e)
                            {
                                logger.error( "Could not store events", e );
                                // How do we handle this? This is a major error!
                            }
                        }
                    }
                } );
            }

            events.add( eventValue );

            return eventValue;
        }
    }