AbstractGenericEntityCollectionModel.java

package fr.openwide.core.wicket.more.model;

import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

import org.apache.wicket.injection.Injector;
import org.apache.wicket.model.LoadableDetachableModel;
import org.apache.wicket.spring.injection.annot.SpringBean;

import com.google.common.base.Supplier;
import com.google.common.collect.Lists;

import fr.openwide.core.jpa.business.generic.model.GenericEntity;
import fr.openwide.core.jpa.business.generic.service.IEntityService;

public abstract class AbstractGenericEntityCollectionModel
		<K extends Serializable & Comparable<K>, E extends GenericEntity<K, ?>, C extends Collection<E>>
		extends LoadableDetachableModel<C> {

	private static final long serialVersionUID = -1768835911782930879L;

	@SpringBean
	private IEntityService entityService;
	
	private transient boolean attached = false;

	private final List<K> idList = Lists.newArrayList();

	private final List<E> unsavedEntityList = Lists.newArrayList();
	
	private final Class<E> clazz;
	
	private final Supplier<? extends C> newCollectionSupplier;
	
	private transient C entityCollection = null;
	
	protected AbstractGenericEntityCollectionModel(Class<E> clazz, Supplier<? extends C> newCollectionSupplier) {
		super();
		Injector.get().inject(this);
		
		this.clazz = clazz;
		this.newCollectionSupplier = newCollectionSupplier;
		setObject(null); // Sets to an empty collection
	}

	protected C createEntityCollection() {
		return newCollectionSupplier.get();
	}

	protected K toId(E entity) {
		return entity.getId();
	}
	
	protected E toEntity(K id) {
		return entityService.getEntity(clazz, id);
	}

	@Override
	protected C load() {
		entityCollection = createEntityCollection();
		
		for (int i = 0, unsavedEntityIndex = 0 ; i < idList.size() ; ++i) {
			K id = idList.get(i);
			
			if (id != null) {
				entityCollection.add(toEntity(id));
			} else {
				assert unsavedEntityList.size() > unsavedEntityIndex;
				E unsavedEntity = unsavedEntityList.get(unsavedEntityIndex);
				assert unsavedEntity != null;
				entityCollection.add(unsavedEntity);
				++unsavedEntityIndex;
			}
		}
		
		attached = true;
		
		return entityCollection;
	}

	/**
	 * WARNING: if the client calls <code>setObject(null)</code>, a subsequent call to <code>getObject()</code>
	 * will not return <code>null</code>, but <em>an empty collection</em>.
	 */
	@Override
	public void setObject(C object) {
		entityCollection = createEntityCollection();
		if (object != null) {
			entityCollection.addAll(object);
		}
		attached = true;
		super.setObject(entityCollection);
	}

	@Override
	public void detach() {
		if (!attached) {
			fixSerializableData();
			return;
		}
		updateSerializableData();
		super.detach();
		attached = false;
	}
	
	private void updateSerializableData() {
		assert entityCollection != null;
		
		// Saves the possible modifications applied to entityCollection
		idList.clear();
		unsavedEntityList.clear();
		
		for (E entity : entityCollection) {
			if (entity.isNew()) {
				unsavedEntityList.add(entity);
				idList.add(null);
			} else {
				// Do nothing with unsavedEntityList here (on purpose)
				K id = toId(entity);
				assert id != null;
				idList.add(id);
			}
		}
		
		entityCollection.clear();
	}

	/**
	 * If an entity has been persisted since this model has been detached, then fix the serializable data
	 * (this may happen if two models reference the same non-persisted entity, for instance)
	 */
	private void fixSerializableData() {
		for (int i = 0, unsavedEntityIndex = 0 ; i < idList.size() ; ++i) {
			K id = idList.get(i);
			
			if (id == null) {
				assert unsavedEntityList.size() > unsavedEntityIndex;
				E unsavedEntity = unsavedEntityList.get(unsavedEntityIndex);
				assert unsavedEntity != null;
				if (unsavedEntity.isNew()) {
					// Do nothing
					++unsavedEntityIndex;
				} else {
					// Fix serializable data
					idList.set(i, toId(unsavedEntity));
					unsavedEntityList.remove(unsavedEntityIndex);
				}
			}
		}
	}

	public List<K> getIdList() {
		return Collections.unmodifiableList(idList);
	}

}