# ManyToManyRelationConfigurer.java

    package org.codefilarete.stalactite.engine.configurer.manytomany;

    import java.lang.reflect.Field;
    import java.lang.reflect.ParameterizedType;
    import java.util.Collection;
    import java.util.function.Supplier;

    import org.codefilarete.reflection.Accessor;
    import org.codefilarete.reflection.AccessorByMethod;
    import org.codefilarete.reflection.AccessorDefinition;
    import org.codefilarete.reflection.Accessors;
    import org.codefilarete.reflection.Mutator;
    import org.codefilarete.reflection.MutatorByMethod;
    import org.codefilarete.reflection.PropertyAccessor;
    import org.codefilarete.reflection.SerializableMutator;
    import org.codefilarete.stalactite.dsl.entity.EntityMappingConfiguration;
    import org.codefilarete.stalactite.dsl.naming.AssociationTableNamingStrategy;
    import org.codefilarete.stalactite.dsl.naming.AssociationTableNamingStrategy.ReferencedColumnNames;
    import org.codefilarete.stalactite.dsl.naming.ColumnNamingStrategy;
    import org.codefilarete.stalactite.dsl.naming.ForeignKeyNamingStrategy;
    import org.codefilarete.stalactite.dsl.naming.JoinColumnNamingStrategy;
    import org.codefilarete.stalactite.dsl.naming.TableNamingStrategy;
    import org.codefilarete.stalactite.dsl.property.CascadeOptions.RelationMode;
    import org.codefilarete.stalactite.engine.configurer.AbstractRelationConfigurer;
    import org.codefilarete.stalactite.engine.configurer.AssociationRecordMapping;
    import org.codefilarete.stalactite.engine.configurer.CascadeConfigurationResult;
    import org.codefilarete.stalactite.engine.configurer.EntityMappingConfigurationWithTable;
    import org.codefilarete.stalactite.engine.configurer.IndexedAssociationRecordMapping;
    import org.codefilarete.stalactite.engine.configurer.builder.PersisterBuilderContext;
    import org.codefilarete.stalactite.engine.configurer.manytomany.ManyToManyRelation.MappedByConfiguration;
    import org.codefilarete.stalactite.engine.configurer.manytomany.ManyToManyRelation.ShiftedMappedByConfiguration;
    import org.codefilarete.stalactite.engine.configurer.onetomany.FirstPhaseCycleLoadListener;
    import org.codefilarete.stalactite.engine.runtime.AssociationRecord;
    import org.codefilarete.stalactite.engine.runtime.AssociationRecordPersister;
    import org.codefilarete.stalactite.engine.runtime.AssociationTable;
    import org.codefilarete.stalactite.engine.runtime.ConfiguredRelationalPersister;
    import org.codefilarete.stalactite.engine.runtime.IndexedAssociationRecord;
    import org.codefilarete.stalactite.engine.runtime.IndexedAssociationTable;
    import org.codefilarete.stalactite.engine.runtime.onetomany.AbstractOneToManyWithAssociationTableEngine;
    import org.codefilarete.stalactite.engine.runtime.onetomany.IndexedAssociationTableManyRelationDescriptor;
    import org.codefilarete.stalactite.engine.runtime.onetomany.ManyRelationDescriptor;
    import org.codefilarete.stalactite.engine.runtime.onetomany.OneToManyWithAssociationTableEngine;
    import org.codefilarete.stalactite.engine.runtime.onetomany.OneToManyWithIndexedAssociationTableEngine;
    import org.codefilarete.stalactite.sql.ConnectionConfiguration;
    import org.codefilarete.stalactite.sql.Dialect;
    import org.codefilarete.stalactite.sql.ddl.structure.PrimaryKey;
    import org.codefilarete.stalactite.sql.ddl.structure.Table;
    import org.codefilarete.tool.Nullable;
    import org.codefilarete.tool.Reflections;
    import org.codefilarete.tool.bean.FieldIterator;
    import org.codefilarete.tool.bean.InstanceFieldIterator;
    import org.codefilarete.tool.collection.Iterables;

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

    /**
     * @param <SRC> type of input (left/source entities)
     * @param <TRGT> type of output (right/target entities)
     * @param <SRCID> identifier type of source entities
     * @param <TRGTID> identifier type of target entities
     * @param <C1> collection type of the relation
     * @author Guillaume Mary
     */
    public class ManyToManyRelationConfigurer<SRC, TRGT, SRCID, TRGTID, C1 extends Collection<TRGT>, C2 extends Collection<SRC>>
    	extends AbstractRelationConfigurer<SRC, SRCID, TRGT, TRGTID> {

    	private final ForeignKeyNamingStrategy foreignKeyNamingStrategy;
    	private final JoinColumnNamingStrategy joinColumnNamingStrategy;
    	private final ColumnNamingStrategy indexColumnNamingStrategy;
    	private final AssociationTableNamingStrategy associationTableNamingStrategy;
    	private final PrimaryKey<?, SRCID> leftPrimaryKey;

    	public ManyToManyRelationConfigurer(ConfiguredRelationalPersister<SRC, SRCID> sourcePersister,
    										Dialect dialect,
    										ConnectionConfiguration connectionConfiguration,
    										TableNamingStrategy tableNamingStrategy,
    										ForeignKeyNamingStrategy foreignKeyNamingStrategy,
    										JoinColumnNamingStrategy joinColumnNamingStrategy,
    										ColumnNamingStrategy indexColumnNamingStrategy,
    										AssociationTableNamingStrategy associationTableNamingStrategy,
    										PersisterBuilderContext currentBuilderContext) {
    		super(dialect, connectionConfiguration, sourcePersister, tableNamingStrategy, currentBuilderContext);
    		this.foreignKeyNamingStrategy = foreignKeyNamingStrategy;
    		this.joinColumnNamingStrategy = joinColumnNamingStrategy;
    		this.indexColumnNamingStrategy = indexColumnNamingStrategy;
    		this.associationTableNamingStrategy = associationTableNamingStrategy;
    		this.leftPrimaryKey = sourcePersister.getMapping().getTargetTable().getPrimaryKey();
    	}

    	public void configure(ManyToManyRelation<SRC, TRGT, TRGTID, C1, C2> manyToManyRelation) {

    		RelationMode maintenanceMode = manyToManyRelation.getRelationMode();
    		// selection is always present (else configuration is nonsense !)
    		boolean orphanRemoval = maintenanceMode == RelationMode.ALL_ORPHAN_REMOVAL;
    		boolean writeAuthorized = maintenanceMode != RelationMode.READ_ONLY;

    		ManyToManyAssociationConfiguration<SRC, TRGT, SRCID, TRGTID, C1, C2, ?, ?> associationConfiguration = new ManyToManyAssociationConfiguration<>(manyToManyRelation,
    				sourcePersister,
    				leftPrimaryKey,
    				foreignKeyNamingStrategy,
    				indexColumnNamingStrategy,
    				orphanRemoval, writeAuthorized);

    		ManyToManyWithAssociationTableConfigurer<SRC, TRGT, SRCID, TRGTID, C1, C2, ?, ?> configurer = new ManyToManyWithAssociationTableConfigurer<>(associationConfiguration,
    				associationTableNamingStrategy,
    				dialect,
    				maintenanceMode == RelationMode.ASSOCIATION_ONLY,
    				connectionConfiguration);

    		String relationName = AccessorDefinition.giveDefinition(manyToManyRelation.getCollectionAccessor()).getName();

    		EntityMappingConfiguration<TRGT, TRGTID> targetMappingConfiguration = manyToManyRelation.getTargetMappingConfiguration();
    		if (currentBuilderContext.isCycling(targetMappingConfiguration)) {
    			// cycle detected
    			// we had a second phase load because cycle can hardly be supported by simply joining things together because at one time we will
    			// fall into infinite loop (think to SQL generation of a cycling graph ...)
    			Class<TRGT> targetEntityType = targetMappingConfiguration.getEntityType();
    			// adding the relation to an eventually already existing cycle configurer for the entity
    			ManyToManyCycleConfigurer<TRGT> cycleSolver = (ManyToManyCycleConfigurer<TRGT>)
    					Iterables.find(currentBuilderContext.getBuildLifeCycleListeners(), p -> p instanceof ManyToManyCycleConfigurer && ((ManyToManyCycleConfigurer<?>) p).getEntityType() == targetEntityType);
    			if (cycleSolver == null) {
    				cycleSolver = new ManyToManyCycleConfigurer<>(targetEntityType);
    				currentBuilderContext.addBuildLifeCycleListener(cycleSolver);
    			}
    			cycleSolver.addCycleSolver(relationName, configurer);
    		} else {
    			// NB: even if no table is found in configuration, build(..) will create one
    			Table targetTable = determineTargetTable(associationConfiguration.getManyToManyRelation());
    			ConfiguredRelationalPersister<TRGT, TRGTID> targetPersister = persisterBuilder.buildOrGiveExisting(new EntityMappingConfigurationWithTable<>(targetMappingConfiguration, targetTable));
    			configurer.configure(targetPersister, associationConfiguration.getManyToManyRelation().isFetchSeparately());
    		}
    	}

    	private Table determineTargetTable(ManyToManyRelation<SRC, TRGT, TRGTID, C1, C2> manyToManyRelation) {
    		Table targetTable = manyToManyRelation.getTargetMappingConfiguration().getTable();
    		if (targetTable == null) {
    			targetTable = lookupTableInRegisteredPersisters(manyToManyRelation.getTargetMappingConfiguration().getEntityType());
    		}
    		return targetTable;
    	}

    	/**
    	 * Configurer
    	 */
    	public static class ManyToManyWithAssociationTableConfigurer<SRC, TRGT, SRCID, TRGTID, C1 extends Collection<TRGT>, C2 extends Collection<SRC>,
    			LEFTTABLE extends Table<LEFTTABLE>, RIGHTTABLE extends Table<RIGHTTABLE>> {

    		private final ManyToManyAssociationConfiguration<SRC, TRGT, SRCID, TRGTID, C1, C2, LEFTTABLE, RIGHTTABLE> associationConfiguration;

    		private final AssociationTableNamingStrategy associationTableNamingStrategy;
    		private final Dialect dialect;
    		private final boolean maintainAssociationOnly;
    		private final ConnectionConfiguration connectionConfiguration;

    		private AbstractOneToManyWithAssociationTableEngine<SRC, TRGT, SRCID, TRGTID, C1, ? extends AssociationRecord, ?> associationTableEngine;

    		private ManyToManyWithAssociationTableConfigurer(ManyToManyAssociationConfiguration<SRC, TRGT, SRCID, TRGTID, C1, C2, LEFTTABLE, RIGHTTABLE> associationConfiguration,
    														 AssociationTableNamingStrategy associationTableNamingStrategy,
    														 Dialect dialect,
    														 boolean maintainAssociationOnly,
    														 ConnectionConfiguration connectionConfiguration) {
    			this.associationConfiguration = associationConfiguration;
    			this.associationTableNamingStrategy = associationTableNamingStrategy;
    			this.dialect = dialect;
    			this.maintainAssociationOnly = maintainAssociationOnly;
    			this.connectionConfiguration = connectionConfiguration;
    		}

    		private void prepare(ConfiguredRelationalPersister<TRGT, TRGTID> targetPersister) {
    			// case : Collection mapping without reverse property: an association table is needed
    			RIGHTTABLE rightTable = targetPersister.<RIGHTTABLE>getMapping().getTargetTable();
    			PrimaryKey<RIGHTTABLE, TRGTID> rightPrimaryKey = rightTable.getPrimaryKey();

    			String associationTableName = nullable(associationConfiguration.getManyToManyRelation().getAssociationTableName()).getOr(() -> associationTableNamingStrategy.giveName(associationConfiguration.getAccessorDefinition(),
    					associationConfiguration.getLeftPrimaryKey(), rightPrimaryKey));
    			if (associationConfiguration.getManyToManyRelation().isOrdered()) {
    				assignEngineForIndexedAssociation(rightPrimaryKey, associationTableName, targetPersister);
    			} else {
    				assignEngineForNonIndexedAssociation(rightPrimaryKey, associationTableName, targetPersister);
    			}
    		}

    		/**
    		 * Build the combiner between target entities and source ones.
    		 *
    		 * @param targetClass target entity type, provided to look up for reverse property if no sufficient info was given
    		 * @return null if no information was provided about the reverse side (no bidirectionality)
    		 */
    		private Mutator<TRGT, SRC> buildReverseCombiner(Class<TRGT> targetClass) {
    			MappedByConfiguration<SRC, TRGT, C2> mappedByConfiguration = associationConfiguration.getManyToManyRelation().getMappedByConfiguration();
    			if (mappedByConfiguration.isEmpty()) {
    				// relation is not bidirectional, and not even set by the reverse link, there's nothing to do
    				return null;
    			} else {
    				PropertyAccessor<TRGT, C2> collectionAccessor = associationConfiguration.buildReversePropertyAccessor();
    				if (collectionAccessor == null) {
    					// since some reverse info has been done but not the collection accessor, we try to find the matching property by type
    					FieldIterator targetFields = new InstanceFieldIterator(targetClass);
    					Class<SRC> sourceEntityType = associationConfiguration.getSrcPersister().getClassToPersist();
    					Field reverseField = Iterables.find(targetFields, field -> Collection.class.isAssignableFrom(field.getType())
    							&& ((ParameterizedType) field.getGenericType()).getActualTypeArguments()[0].equals(sourceEntityType));
    					if (reverseField != null) {
    						Nullable<AccessorByMethod<TRGT, C2>> reverseGetterMethod = nullable(Accessors.accessorByMethod(reverseField));
    						if (reverseGetterMethod.isPresent()) {
    							collectionAccessor = new PropertyAccessor<>(reverseGetterMethod.get());
    						} else {
    							Nullable<MutatorByMethod<TRGT, C2>> reverseSetterMethod = nullable(Accessors.mutatorByMethod(reverseField));
    							if (reverseSetterMethod.isPresent()) {
    								collectionAccessor = new PropertyAccessor<>(reverseSetterMethod.get());
    							}
    						}
    					} // else : relation is not bidirectional, or not a usual one, may be set by reverse link
    				}

    				Nullable<SerializableMutator<TRGT, SRC>> configuredCombiner = nullable(mappedByConfiguration.getReverseCombiner());
    				Mutator<TRGT, SRC> result;
    				if (collectionAccessor == null) {
    					result = configuredCombiner.get();
    				} else {
    					// collection factory is in priority the one configured
    					Supplier<C2> reverseCollectionFactory = mappedByConfiguration.getReverseCollectionFactory();
    					if (reverseCollectionFactory == null) {
    						Class<C2> collectionType = AccessorDefinition.giveDefinition(collectionAccessor).getMemberType();
    						reverseCollectionFactory = Reflections.giveCollectionFactory(collectionType);
    					}
    					PropertyAccessor<TRGT, C2> finalCollectionAccessor = collectionAccessor;
    					SerializableMutator<TRGT, SRC> combiner = configuredCombiner.getOr((TRGT trgt, SRC src) -> {
    						// collectionAccessor can't be null due to nullable check
    						finalCollectionAccessor.get(trgt).add(src);
    					});

    					Supplier<C2> effectiveCollectionFactory = reverseCollectionFactory;
    					result = (TRGT trgt, SRC src) -> {
    						// we call the collection factory to ensure that property is initialized
    						if (finalCollectionAccessor.get(trgt) == null) {
    							finalCollectionAccessor.set(trgt, effectiveCollectionFactory.get());
    						}
    						// Note that combiner can't be null here thanks to nullable(..) check
    						combiner.set(trgt, src);
    					};
    				}

    				if (mappedByConfiguration instanceof ManyToManyRelation.ShiftedMappedByConfiguration) {
    					Accessor shifter = ((ShiftedMappedByConfiguration) mappedByConfiguration).getShifter();
    					return (trgt, src) -> {
    						SRC src1 = (SRC) shifter.get(src);
    						result.set(trgt, src1);
    					};
    				} else {
    					return result;
    				}
    			}
    		}

    		String configure(ConfiguredRelationalPersister<TRGT, TRGTID> targetPersister, boolean loadSeparately) {
    			prepare(targetPersister);
    			String relationJoinNodeName = associationTableEngine.addSelectCascade(associationConfiguration.getSrcPersister(), loadSeparately);
    			addWriteCascades(associationTableEngine, targetPersister);
    			return relationJoinNodeName;
    		}

    		public CascadeConfigurationResult<SRC,TRGT> configureWithSelectIn2Phases(ConfiguredRelationalPersister<TRGT, TRGTID> targetPersister,
    																				 FirstPhaseCycleLoadListener<SRC, TRGTID> firstPhaseCycleLoadListener) {
    			prepare(targetPersister);
    			associationTableEngine.addSelectCascadeIn2Phases(firstPhaseCycleLoadListener);
    			addWriteCascades(associationTableEngine, targetPersister);
    			return new CascadeConfigurationResult<>(associationTableEngine.getManyRelationDescriptor().getRelationFixer(), associationConfiguration.getSrcPersister());
    		}

    		private void addWriteCascades(AbstractOneToManyWithAssociationTableEngine<SRC, TRGT, SRCID, TRGTID, C1, ? extends AssociationRecord, ? extends AssociationTable> oneToManyWithAssociationTableEngine, ConfiguredRelationalPersister<TRGT, TRGTID> targetPersister) {
    			if (associationConfiguration.isWriteAuthorized()) {
    				oneToManyWithAssociationTableEngine.addInsertCascade(maintainAssociationOnly, targetPersister);
    				oneToManyWithAssociationTableEngine.addUpdateCascade(associationConfiguration.isOrphanRemoval(), maintainAssociationOnly, targetPersister);
    				oneToManyWithAssociationTableEngine.addDeleteCascade(associationConfiguration.isOrphanRemoval(), dialect, targetPersister);
    			}
    		}

    		private <ASSOCIATIONTABLE extends AssociationTable<ASSOCIATIONTABLE, LEFTTABLE, RIGHTTABLE, SRCID, TRGTID>>
    		void assignEngineForNonIndexedAssociation(
    				PrimaryKey<RIGHTTABLE, TRGTID> rightPrimaryKey,
    				String associationTableName,
    				ConfiguredRelationalPersister<TRGT, TRGTID> targetPersister) {

    			// we don't create foreign key for table-per-class because source columns should reference different tables (the one
    			// per entity) which databases do not allow
    			boolean createOneSideForeignKey = !(associationConfiguration.getManyToManyRelation().isSourceTablePerClassPolymorphic());
    			boolean createManySideForeignKey = !associationConfiguration.getManyToManyRelation().isTargetTablePerClassPolymorphic();
    			ReferencedColumnNames<LEFTTABLE, RIGHTTABLE> columnNames = associationTableNamingStrategy.giveColumnNames(
    					associationConfiguration.getAccessorDefinition(),
    					associationConfiguration.getLeftPrimaryKey(),
    					rightPrimaryKey);

    			if (associationConfiguration.getManyToManyRelation().getSourceJoinColumnName() != null) {
    				columnNames.setLeftColumnName(Iterables.first(associationConfiguration.getLeftPrimaryKey().getColumns()), associationConfiguration.getManyToManyRelation().getSourceJoinColumnName());
    			}
    			if (associationConfiguration.getManyToManyRelation().getSourceJoinColumnName() != null) {
    				columnNames.setRightColumnName(Iterables.first(rightPrimaryKey.getColumns()), associationConfiguration.getManyToManyRelation().getTargetJoinColumnName());
    			}

    			ASSOCIATIONTABLE intermediaryTable = (ASSOCIATIONTABLE) new AssociationTable<ASSOCIATIONTABLE, LEFTTABLE, RIGHTTABLE, SRCID, TRGTID>(
    					associationConfiguration.getLeftPrimaryKey().getTable().getSchema(),
    					associationTableName,
    					associationConfiguration.getLeftPrimaryKey(),
    					rightPrimaryKey,
    					columnNames,
    					associationConfiguration.getForeignKeyNamingStrategy(),
    					createOneSideForeignKey,
    					createManySideForeignKey
    			);

    			AssociationRecordPersister<AssociationRecord, ASSOCIATIONTABLE> associationPersister = new AssociationRecordPersister<>(
    					new AssociationRecordMapping<>(intermediaryTable,
    							associationConfiguration.getSrcPersister().getMapping().getIdMapping().getIdentifierAssembler(),
    							targetPersister.getMapping().getIdMapping().getIdentifierAssembler()),
    					dialect,
    					connectionConfiguration);

    			ManyRelationDescriptor<SRC, TRGT, C1> manyRelationDescriptor = new ManyRelationDescriptor<>(
    					associationConfiguration.getCollectionGetter(),
    					associationConfiguration.getSetter()::set,
    					associationConfiguration.getCollectionFactory(),
    					buildReverseCombiner(targetPersister.getClassToPersist()));

    			associationTableEngine = new OneToManyWithAssociationTableEngine<>(
    					associationConfiguration.getSrcPersister(),
    					targetPersister,
    					manyRelationDescriptor,
    					associationPersister,
    					dialect.getWriteOperationFactory());
    		}

    		private <ASSOCIATIONTABLE extends IndexedAssociationTable<ASSOCIATIONTABLE, LEFTTABLE, RIGHTTABLE, SRCID, TRGTID>>
    		void assignEngineForIndexedAssociation(
    				PrimaryKey<RIGHTTABLE, TRGTID> rightPrimaryKey,
    				String associationTableName,
    				ConfiguredRelationalPersister<TRGT, TRGTID> targetPersister) {

    			ManyToManyRelation<SRC, TRGT, TRGTID, C1, C2> relation = associationConfiguration.getManyToManyRelation();

    			// we don't create foreign key for table-per-class because source columns should reference different tables (the one
    			// per entity) which databases do not allow
    			boolean createOneSideForeignKey = !relation.isSourceTablePerClassPolymorphic();
    			boolean createManySideForeignKey = !relation.isTargetTablePerClassPolymorphic();
    			ReferencedColumnNames<LEFTTABLE, RIGHTTABLE> columnNames = associationTableNamingStrategy.giveColumnNames(
    					associationConfiguration.getAccessorDefinition(),
    					associationConfiguration.getLeftPrimaryKey(),
    					rightPrimaryKey);

    			String indexingColumnName = nullable(relation.getIndexingColumnName()).getOr(() -> associationConfiguration.getIndexColumnNamingStrategy().giveName(associationConfiguration.getAccessorDefinition()));

    			// NB: index column is part of the primary key
    			ASSOCIATIONTABLE intermediaryTable = (ASSOCIATIONTABLE) new IndexedAssociationTable<ASSOCIATIONTABLE, LEFTTABLE, RIGHTTABLE, SRCID, TRGTID>(
    					associationConfiguration.getLeftPrimaryKey().getTable().getSchema(),
    					associationTableName,
    					associationConfiguration.getLeftPrimaryKey(),
    					rightPrimaryKey,
    					columnNames,
    					associationConfiguration.getForeignKeyNamingStrategy(),
    					createOneSideForeignKey,
    					createManySideForeignKey,
    					indexingColumnName);

    			intermediaryTable.addForeignKey(associationConfiguration.getForeignKeyNamingStrategy()::giveName,
    					intermediaryTable.getOneSideForeignKey(), associationConfiguration.getLeftPrimaryKey());

    			AssociationRecordPersister<IndexedAssociationRecord, ASSOCIATIONTABLE> indexedAssociationPersister =
    					new AssociationRecordPersister<>(
    							new IndexedAssociationRecordMapping<>(intermediaryTable,
    									associationConfiguration.getSrcPersister().getMapping().getIdMapping().getIdentifierAssembler(),
    									targetPersister.getMapping().getIdMapping().getIdentifierAssembler(),
    									intermediaryTable.getLeftIdentifierColumnMapping(),
    									intermediaryTable.getRightIdentifierColumnMapping()),
    							dialect,
    							connectionConfiguration);

    			IndexedAssociationTableManyRelationDescriptor<SRC, TRGT, C1, SRCID> manyRelationDescriptor = new IndexedAssociationTableManyRelationDescriptor<>(
    					associationConfiguration.getCollectionGetter(),
    					associationConfiguration.getSetter()::set,
    					associationConfiguration.getCollectionFactory(),
    					buildReverseCombiner(targetPersister.getClassToPersist()),
    					associationConfiguration.getSrcPersister()::getId
    			);

    			associationTableEngine = new OneToManyWithIndexedAssociationTableEngine<>(
    					associationConfiguration.getSrcPersister(),
    					targetPersister,
    					manyRelationDescriptor,
    					indexedAssociationPersister,
    					intermediaryTable.getIndexColumn(),
    					dialect.getWriteOperationFactory());
    		}
    	}
    }