/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
 */
package org.hibernate.id;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import org.hibernate.HibernateException;
import org.hibernate.boot.model.relational.Database;
import org.hibernate.boot.model.relational.ExportableProducer;
import org.hibernate.engine.spi.SharedSessionContractImplementor;

For composite identifiers, defines a number of "nested" generations that
need to happen to "fill" the identifier property(s).

This generator is used implicitly for all composite identifier scenarios if an
explicit generator is not in place.  So it make sense to discuss the various 
potential scenarios:


"embedded" composite identifier - this is possible only in HBM mappings as <composite-id/> (notice the lack of both a name and class attribute declarations). The term "embedded" here refers to the Hibernate usage which is actually the exact opposite of the JPA meaning of "embedded". Essentially this means that the entity class itself holds the named composite pk properties. This is very similar to the JPA @IdClass usage, though without a separate pk-class for loading. 

pk-class as entity attribute - this is possible in both annotations (@EmbeddedId) and HBM mappings (<composite-id name="idAttributeName" class="PkClassName"/>) 

"embedded" composite identifier with a pk-class - this is the JPA @IdClass use case and is only possible in annotations 

 Most of the grunt work is done in Component. 
Author:
Steve Ebersole/**
 * For composite identifiers, defines a number of "nested" generations that
 * need to happen to "fill" the identifier property(s).
 * <p/>
 * This generator is used implicitly for all composite identifier scenarios if an
 * explicit generator is not in place.  So it make sense to discuss the various 
 * potential scenarios:<ul>
 * <li>
 * <i>"embedded" composite identifier</i> - this is possible only in HBM mappings
 * as {@code <composite-id/>} (notice the lack of both a name and class attribute
 * declarations).  The term {@link org.hibernate.mapping.Component#isEmbedded() "embedded"}
 * here refers to the Hibernate usage which is actually the exact opposite of the JPA
 * meaning of "embedded".  Essentially this means that the entity class itself holds
 * the named composite pk properties.  This is very similar to the JPA {@code @IdClass}
 * usage, though without a separate pk-class for loading.
 * </li>
 * <li>
 * <i>pk-class as entity attribute</i> - this is possible in both annotations ({@code @EmbeddedId})
 * and HBM mappings ({@code <composite-id name="idAttributeName" class="PkClassName"/>})
 * </li>
 * <li>
 * <i>"embedded" composite identifier with a pk-class</i> - this is the JPA {@code @IdClass} use case
 * and is only possible in annotations
 * </li>
 * </ul>
 * <p/>
 * Most of the grunt work is done in {@link org.hibernate.mapping.Component}.
 *
 * @author Steve Ebersole
 */
public class CompositeNestedGeneratedValueGenerator implements IdentifierGenerator, Serializable, IdentifierGeneratorAggregator {
	
Contract for declaring how to locate the context for sub-value injection.
/**
	 * Contract for declaring how to locate the context for sub-value injection.
	 */
	public interface GenerationContextLocator {
		
Given the incoming object, determine the context for injecting back its generated
id sub-values.
Params:
session – The current session
incomingObject – The entity for which we are generating id
Returns:
The injection context/**
		 * Given the incoming object, determine the context for injecting back its generated
		 * id sub-values.
		 *
		 * @param session The current session
		 * @param incomingObject The entity for which we are generating id
		 *
		 * @return The injection context
		 */
		Serializable locateGenerationContext(SharedSessionContractImplementor session, Object incomingObject);
	}

	
Contract for performing the actual sub-value generation, usually injecting it into the determined context /**
	 * Contract for performing the actual sub-value generation, usually injecting it into the
	 * determined {@link GenerationContextLocator#locateGenerationContext context}
	 */
	public interface GenerationPlan extends ExportableProducer {
		
Execute the value generation.
Params:
session – The current session
incomingObject – The entity for which we are generating id
injectionContext – The context into which the generated value can be injected/**
		 * Execute the value generation.
		 *
		 * @param session The current session
		 * @param incomingObject The entity for which we are generating id
		 * @param injectionContext The context into which the generated value can be injected
		 */
		void execute(SharedSessionContractImplementor session, Object incomingObject, Object injectionContext);
	}

	private final GenerationContextLocator generationContextLocator;
	private List<GenerationPlan> generationPlans = new ArrayList<>();

	public CompositeNestedGeneratedValueGenerator(GenerationContextLocator generationContextLocator) {
		this.generationContextLocator = generationContextLocator;
	}

	public void addGeneratedValuePlan(GenerationPlan plan) {
		generationPlans.add( plan );
	}

	@Override
	public Serializable generate(SharedSessionContractImplementor session, Object object) throws HibernateException {
		final Serializable context = generationContextLocator.locateGenerationContext( session, object );

		for ( Object generationPlan : generationPlans ) {
			final GenerationPlan plan = (GenerationPlan) generationPlan;
			plan.execute( session, object, context );
		}

		return context;
	}

	@Override
	public void registerExportables(Database database) {
		for (GenerationPlan plan : generationPlans) {
			plan.registerExportables( database );
		}
	}
}