# JoinTablePolymorphicRelationJoinNode.java

    package org.codefilarete.stalactite.engine.runtime.load;

    import javax.annotation.Nullable;
    import java.util.HashSet;
    import java.util.Set;
    import java.util.function.Function;

    import org.codefilarete.reflection.Accessor;
    import org.codefilarete.stalactite.engine.runtime.load.EntityJoinTree.JoinType;
    import org.codefilarete.stalactite.engine.runtime.load.EntityTreeInflater.RelationIdentifier;
    import org.codefilarete.stalactite.engine.runtime.load.EntityTreeInflater.TreeInflationContext;
    import org.codefilarete.stalactite.engine.runtime.load.JoinRowConsumer.ForkJoinRowConsumer;
    import org.codefilarete.stalactite.sql.ddl.structure.Column;
    import org.codefilarete.stalactite.sql.ddl.structure.Key;
    import org.codefilarete.stalactite.sql.ddl.structure.Table;
    import org.codefilarete.stalactite.sql.result.BeanRelationFixer;
    import org.codefilarete.stalactite.sql.result.ColumnedRow;
    import org.codefilarete.tool.Reflections;

    import static org.codefilarete.tool.Nullable.nullable;

    /**
     * Particular {@link JoinNode} made to handle relation from an entity to a collection of some another polymorphic one. Actually relation doesn't
     * make the complexity of that class: polymorphic entity instantiation is the core focus of it. Here are the hot spots:
     * identifier is given by the subclass which find its id in the row (see {@link JoinTablePolymorphicRelationJoinRowConsumer#giveIdentifier}),
     * and while doing it, it remembers which consumer made it. Then while instantiating entity we invoke it to get right entity type (parent mapping
     * would only give parent entity, which, out of being a wrong approach, can be an abstract type). Then instance is filled up with parent properties
     * by calling merging method (see line 98).
     * Finally, {@link JoinTablePolymorphicRelationJoinRowConsumer} must extend {@link ForkJoinRowConsumer} to give next branch to be consumed by
     * {@link EntityTreeInflater} to avoid "dead" branch to be read : we give it according to the consumer which found the identifier.
     *
     * @author Guillaume Mary
     */
    public class JoinTablePolymorphicRelationJoinNode<C, T1 extends Table, T2 extends Table, JOINTYPE, I> extends RelationJoinNode<C, T1, T2, JOINTYPE, I> {

    	private final Set<SubPersister<? extends C>> subPersisters = new HashSet<>();

    	public JoinTablePolymorphicRelationJoinNode(JoinNode<?, T1> parent,
    												Accessor<?, ?> propertyAccessor,
    												Key<T1, JOINTYPE> leftJoinColumn,
    												Key<T2, JOINTYPE> rightJoinColumn,
    												JoinType joinType,
    												Set<Column<T2, ?>> columnsToSelect,
    												@Nullable String tableAlias,
    												EntityInflater<C, I> entityInflater,
    												BeanRelationFixer<Object, C> beanRelationFixer,
    												@Nullable Function<ColumnedRow, ?> relationIdentifierProvider) {
    		super(parent, propertyAccessor, leftJoinColumn, rightJoinColumn, joinType, columnsToSelect, tableAlias, entityInflater, beanRelationFixer, relationIdentifierProvider);
    	}

    	@Override
    	public JoinTablePolymorphicRelationJoinRowConsumer toConsumer(JoinNode<C, T2> joinNode) {
    		DefaultRelationJoinRowConsumer<C, I> parentRowConsumer = (DefaultRelationJoinRowConsumer<C, I>) super.toConsumer(joinNode);
    		return new JoinTablePolymorphicRelationJoinRowConsumer(joinNode, parentRowConsumer, getConsumptionListener());
    	}

    	public <D extends C> void addSubPersisterJoin(PolymorphicMergeJoinRowConsumer<D, I> subPersisterJoin) {
    		this.subPersisters.add(new SubPersister<>(subPersisterJoin));
    	}

    	private class SubPersister<D extends C> {

    		private final PolymorphicMergeJoinRowConsumer<D, I> subPersisterMergeConsumer;

    		public SubPersister(PolymorphicMergeJoinRowConsumer<D, I> subPersisterMergeConsumer) {
    			this.subPersisterMergeConsumer = subPersisterMergeConsumer;
    		}
    	}

    	public class JoinTablePolymorphicRelationJoinRowConsumer implements RelationJoinRowConsumer<C, I>, ForkJoinRowConsumer {

    		private final ThreadLocal<RowIdentifier<? extends C>> currentlyFoundConsumer = new ThreadLocal<>();

    		private final JoinNode<C, ?> joinNode;

    		private final DefaultRelationJoinRowConsumer<C, I> parentRowConsumer;

    		/** Optional listener of ResultSet decoding */
    		@Nullable
    		private final EntityTreeJoinNodeConsumptionListener<C> consumptionListener;

    		private JoinTablePolymorphicRelationJoinRowConsumer(JoinNode<C, ?> joinNode,
                                                                DefaultRelationJoinRowConsumer<C, I> parentRowConsumer,
                                                                @Nullable EntityTreeJoinNodeConsumptionListener<C> consumptionListener) {
    			this.joinNode = joinNode;
    			this.parentRowConsumer = parentRowConsumer;
    			this.consumptionListener = consumptionListener;
    		}

    		@Override
    		public JoinNode<C, ?> getNode() {
    			return joinNode;
    		}

    		@Override
    		public EntityReference<C, I> applyRelatedEntity(EntityReference<?, ?> parentJoinEntity, ColumnedRow row, TreeInflationContext context) {
    			RowIdentifier<? extends C> rowIdentifier = giveIdentifier();
    			currentlyFoundConsumer.set(rowIdentifier);
    			if (rowIdentifier != null) {
    				I rightIdentifier = rowIdentifier.entityIdentifier;
    				// we avoid treating twice same relation, overall to avoid adding twice same instance to a collection (one-to-many list cases)
    				// in case of multiple collections in ResultSet because it creates similar data (through cross join) which are treated as many as
    				// collections cross with each other. This also works for one-to-one relations but produces no bugs. It can also be seen as a performance
    				// enhancement even if it hasn't been measured.
    				RelationIdentifier eventuallyApplied = new RelationIdentifier(parentJoinEntity.getIdentifier(), getEntityType(), rightIdentifier, this);
    				// primary key null means no entity => nothing to do
    				if (rightIdentifier != null && context.isTreatedOrAppend(eventuallyApplied)) {
    					C rightEntity = context.giveEntityFromCache(getEntityType(), rightIdentifier, () -> {
    						ColumnedRow subInflaterRow = EntityTreeInflater.currentContext().getDecoder(rowIdentifier.rowConsumer.getNode());
    						C entity = rowIdentifier.rowConsumer.transform(subInflaterRow);
    						// We have to apply parent properties on created bean by subclass, because sub-transformer doesn't contain them
    						parentRowConsumer.getRowTransformer().applyRowToBean(row, entity);
    						return entity;
    					});
    					getBeanRelationFixer().apply(parentJoinEntity.getEntity(), rightEntity);
    					if (this.consumptionListener != null) {
    						this.consumptionListener.onNodeConsumption(rightEntity, row);
    					}
    					return new EntityReference<>(rightEntity, rightIdentifier);
    				}
    			}
    			return null;
    		}

    		@Nullable
    		/* Optimized, from 530 000 nanos to 65 000 nanos at 1st exec, from 40 000 nanos to 12 000 nanos on usual run */
    		private RowIdentifier<? extends C> giveIdentifier() {
    			// @Optimized : use for & return instead of stream().map().filter(notNull).findFirst()
    			for (SubPersister<?> pawn : subPersisters) {
    				ColumnedRow subInflaterRow = EntityTreeInflater.currentContext().getDecoder(pawn.subPersisterMergeConsumer.getNode());
    				I assemble = pawn.subPersisterMergeConsumer.giveIdentifier(subInflaterRow);
    				if (assemble != null) {
    					return new RowIdentifier<>(assemble, pawn.subPersisterMergeConsumer);
    				}
    			}
    			return null;
    		}

    		@Override
    		public JoinRowConsumer giveNextConsumer() {
    			return nullable(currentlyFoundConsumer.get()).map(rowIdentifier -> rowIdentifier.rowConsumer).get();
    		}

    		@Override
    		public void afterRowConsumption(TreeInflationContext context) {
    			currentlyFoundConsumer.remove();
    		}

    		private class RowIdentifier<D extends C> {

    			private final I entityIdentifier;
    			private final PolymorphicMergeJoinRowConsumer<D, I> rowConsumer;

    			private RowIdentifier(I entityIdentifier, PolymorphicMergeJoinRowConsumer<D, I> rowConsumer) {
    				this.entityIdentifier = entityIdentifier;
    				this.rowConsumer = rowConsumer;
    			}
    		}

    		/**
    		 * Implemented for debug. DO NOT RELY ON IT for anything else.
    		 */
    		@Override
    		public String toString() {
    			return Reflections.toString(this.getClass());
    		}
    	}
    }