class MassIndexer {

	// MassIndexer parameters/attributes
	boolean optimizeBefore = false;
	boolean purgeBefore = false;
	boolean optimizeAfter = false;

	Collection<Class<?>> rootEntityTypes = null;
	PojoMappingDelegate delegate = null;// = ...

	MappingWorkExecutor mappingWorkExecutor = delegate.createMappingWorkExecutor();

	public void execute() {
		if ( purgeBefore ) {
			mappingWorkExecutor.purge( rootEntityTypes ).join();
		}
		if ( optimizeBefore ) {
			mappingWorkExecutor.optimize( rootEntityTypes ).join();
		}

		// Index
		// for each IdentifierConsumerDocumentProducer
		{
			List<?> entities = ...;
			indexingMonitor.entitiesLoaded( entities.size() );
			SessionContext sessionContext;
			SessionWorkExecutor sessionWorkExecutor = delegate.createSessionWorkExecutor( sessionContext );
			List<CompletableFuture<?>> completableFutures = new ArrayList<>(  );

			for ( Object entity : entities ) {
				CompletableFuture<?> entityIndexedFuture = sessionWorkExecutor.add( entity );
				completableFutures.add( entityIndexedFuture );
			}
			indexingMonitor.documentBuilt( entities.size() );

			CompletableFuture.allOf( completableFutures.toArray( new CompletableFuture[0] ) )
					.join();
			indexingMonitor.documentAdded( entities.size() );
		}

		mappingWorkExecutor.flush( rootEntityTypes ).join();

		if ( optimizeAfter ) {
			mappingWorkExecutor.optimize( rootEntityTypes ).join();
		}

	}
}

interface IndexingMonitor {
	void addToTotalCount(long increment); // Already taken care of

	void documentsAdded(long increment); // see above

	void documentsBuilt(int increment); // see above

	void entitiesLoaded(int increment); // see above

	void indexingCompleted(); // Already taken care of
}

interface PojoMappingDelegate {

	// ...

	MappingWorkExecutor createMappingWorkExecutor();

	SessionWorkExecutor createSessionWorkExecutor(SessionContext ctx);

}

interface MappingWorkExecutor {
		CompletableFuture<?> optimize(Collection<Class<?>> types);
		CompletableFuture<?> purge(Collection<Class<?>> types);
		CompletableFuture<?> flush(Collection<Class<?>> types);
}

interface SessionWorkExecutor {

	CompletableFuture<?> add(Object id, Object entity);
	CompletableFuture<?> add(Object entity);

}

class SessionWorkExecutorImpl implements SessionWorkExecutor {

	Map<Class<?>, IndexWorkExecutor> indexWorkExecutor;

	CompletableFuture<?> add(Object id, Object entity) {
		// 1. retrieve and cache the appropriate IndexWorkExecutor (similarly to what we do with PojoTypeWorkPlans in PojoWorkPlan)

		// 2. add to index
		// see PojoWorkPlan.add and PojoTypeWorkPlan.add and IndexedEntityWorkPlan.sendWorkToDelegate, in particular, for implementation
	}

}


/// BACKEND SPIs


// This interface already exists
interface IndexManagerImplementor {

	// ...

	CompletableFuture<?> optimize();
	CompletableFuture<?> purge();
	CompletableFuture<?> flush();

	IndexWorkExecutor createWorkExecutor();
}

interface IndexWorkExecutor {

	CompletableFuture<?> add(DocumentReferenceProvider documentReferenceProvider, DocumentContributor<D> documentContributor);

}