# ManyToManyRelation.java

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

    import java.util.Collection;
    import java.util.function.BooleanSupplier;
    import java.util.function.Supplier;
    import javax.annotation.Nullable;

    import org.codefilarete.reflection.Accessor;
    import org.codefilarete.reflection.AccessorChain;
    import org.codefilarete.reflection.AccessorChain.ValueInitializerOnNullValue;
    import org.codefilarete.reflection.ReadWriteAccessorChain;
    import org.codefilarete.reflection.ReadWritePropertyAccessPoint;
    import org.codefilarete.reflection.SerializablePropertyAccessor;
    import org.codefilarete.reflection.SerializablePropertyMutator;
    import org.codefilarete.stalactite.dsl.PolymorphismPolicy;
    import org.codefilarete.stalactite.dsl.entity.EntityMappingConfiguration;
    import org.codefilarete.stalactite.dsl.entity.EntityMappingConfigurationProvider;
    import org.codefilarete.stalactite.dsl.property.CascadeOptions.RelationMode;
    import org.codefilarete.tool.Reflections;

    /**
     *
     * @param <SRC> the "one" type
     * @param <TRGT> the "many" type
     * @param <TRGTID> identifier type of TRGT
     * @param <C1> the "many" collection type
     */
    public class ManyToManyRelation<SRC, TRGT, TRGTID, C1 extends Collection<TRGT>, C2 extends Collection<SRC>> {

    	/** The method that gives the "many" entities from the "one" entity */
    	private final ReadWritePropertyAccessPoint<SRC, C1> collectionAccessor;

    	private final BooleanSupplier sourceTablePerClassPolymorphic;

    	/** Configuration used for "many" side beans persistence */
    	private final EntityMappingConfigurationProvider<TRGT, TRGTID> targetMappingConfiguration;

    	/** Default relation mode is {@link RelationMode#ALL} */
    	private RelationMode relationMode = RelationMode.ALL;

    	/** Optional provider of collection instance to be used if collection value is null */
    	private Supplier<C1> collectionFactory;

    	private final MappedByConfiguration<SRC, TRGT, C2> mappedByConfiguration;

    	/**
    	 * Indicates that relation must be loaded in same main query (through join) or in some separate query
    	 */
    	private boolean fetchSeparately;

    	/**
    	 * Indicates if target instances are indexed in their {@link Collection} (meaning that it is capable of storing order)
    	 */
    	private boolean ordered = false;

    	private String indexingColumnName;

    	/**
    	 *
    	 * @param collectionAccessor provider of the property to be persisted
    	 * @param sourceTablePerClassPolymorphic indicates that source is table-per-class polymorphic
    	 * @param targetMappingConfiguration persistence configuration provider of entities stored in the target collection
    	 */
    	public ManyToManyRelation(ReadWritePropertyAccessPoint<SRC, C1> collectionAccessor,
    							  BooleanSupplier sourceTablePerClassPolymorphic,
    							  EntityMappingConfigurationProvider<? super TRGT, TRGTID> targetMappingConfiguration) {
    		this.collectionAccessor = collectionAccessor;
    		this.sourceTablePerClassPolymorphic = sourceTablePerClassPolymorphic;
    		this.targetMappingConfiguration = (EntityMappingConfigurationProvider<TRGT, TRGTID>) targetMappingConfiguration;
    		this.mappedByConfiguration = new MappedByConfiguration<>();
    	}

    	public ManyToManyRelation(ReadWritePropertyAccessPoint<SRC, C1> collectionAccessor,
    							  BooleanSupplier sourceTablePerClassPolymorphic,
    							  EntityMappingConfigurationProvider<? super TRGT, TRGTID> targetMappingConfiguration,
    							  MappedByConfiguration<?, TRGT, ?> mappedByConfiguration) {
    		this.collectionAccessor = collectionAccessor;
    		this.sourceTablePerClassPolymorphic = sourceTablePerClassPolymorphic;
    		this.targetMappingConfiguration = (EntityMappingConfigurationProvider<TRGT, TRGTID>) targetMappingConfiguration;
    		// Note that this cast is wrong, but left for simplicity: this constructor is used for embedded many-to-many relation, which means that the SRC
    		// type is the one that embed another one which contains the relation. In such configuration, the relation actually points to the embeddable
    		// type, not the one that embeds the relation. This the mappedBy(..) config does the same: it point to the embeddable type, not the SRC type.
    		// But fixing it has a lot of impacts due to the necessity to replace MappedByConfiguration "SRC" type by a generic <?> one with has its own
    		// complexity. I consider all these impacts doesn't worth it and I prefer to force this cast, even wrong.
    		this.mappedByConfiguration = (MappedByConfiguration<SRC, TRGT, C2>) mappedByConfiguration;
    	}

    	public ReadWritePropertyAccessPoint<SRC, C1> getCollectionAccessor() {
    		return collectionAccessor;
    	}

    	public boolean isSourceTablePerClassPolymorphic() {
    		return sourceTablePerClassPolymorphic.getAsBoolean();
    	}

    	/** @return the configuration used for "many" side beans persistence */
    	public EntityMappingConfiguration<TRGT, TRGTID> getTargetMappingConfiguration() {
    		return targetMappingConfiguration.getConfiguration();
    	}

    	public boolean isTargetTablePerClassPolymorphic() {
    		return getTargetMappingConfiguration().getPolymorphismPolicy() instanceof PolymorphismPolicy.TablePerClassPolymorphism;
    	}

    	public RelationMode getRelationMode() {
    		return relationMode;
    	}

    	public void setRelationMode(RelationMode relationMode) {
    		this.relationMode = relationMode;
    	}

    	@Nullable
    	public Supplier<C1> getCollectionFactory() {
    		return collectionFactory;
    	}

    	public void setCollectionFactory(Supplier<C1> collectionFactory) {
    		this.collectionFactory = collectionFactory;
    	}

    	public MappedByConfiguration<SRC, TRGT, C2> getMappedByConfiguration() {
    		return mappedByConfiguration;
    	}

    	@Nullable
    	public String getAssociationTableName() {
    		return this.mappedByConfiguration.getAssociationTableName();
    	}

    	public void setAssociationTableName(@Nullable String tableName) {
    		this.mappedByConfiguration.setAssociationTableName(tableName);
    	}

    	@Nullable
    	public String getSourceJoinColumnName() {
    		return this.mappedByConfiguration.getSourceJoinColumnName();
    	}

    	public void setSourceJoinColumnName(@Nullable String sourceJoinColumnName) {
    		this.mappedByConfiguration.setSourceJoinColumnName(sourceJoinColumnName);
    	}

    	@Nullable
    	public String getTargetJoinColumnName() {
    		return this.mappedByConfiguration.getTargetJoinColumnName();
    	}

    	public void setTargetJoinColumnName(@Nullable String targetJoinColumnName) {
    		this.mappedByConfiguration.setTargetJoinColumnName(targetJoinColumnName);
    	}

    	public void setIndexingColumnName(String columnName) {
    		ordered();
    		this.indexingColumnName = columnName;
    	}

    	@Nullable
    	public String getIndexingColumnName() {
    		return indexingColumnName;
    	}

    	public boolean isOrdered() {
    		return ordered;
    	}

    	public void setOrdered(boolean ordered) {
    		this.ordered = ordered;
    	}

    	public void ordered() {
    		this.ordered = true;
    	}

    	public boolean isFetchSeparately() {
    		return fetchSeparately;
    	}

    	public void setFetchSeparately(boolean fetchSeparately) {
    		this.fetchSeparately = fetchSeparately;
    	}

    	public void fetchSeparately() {
    		setFetchSeparately(true);
    	}

    	/**
    	 * Clones this object to create a new one with the given accessor as prefix of current one.
    	 * Made to shift current instance with an accessor prefix. Used for embeddable objects with relation to make the relation being accessible
    	 * from the "root" entity.
    	 *
    	 * @param accessor the prefix of the clone to be created
    	 * @return a clones of this instance prefixed with the given accessor
    	 * @param <E> the root entity type that owns the embeddable which has this relation
    	 */
    	public <E, S extends Collection<E>> ManyToManyRelation<E, TRGT, TRGTID, C1, S> embedInto(Accessor<E, SRC> accessor, Class<SRC> embeddedType) {
    		AccessorChain<E, C1> shiftedTargetProvider = new AccessorChain<>(accessor, collectionAccessor);
    		shiftedTargetProvider.setNullValueHandler(new ValueInitializerOnNullValue() {
    			@Override
    			protected <T> T newInstance(Accessor<?, T> segmentAccessor, Class<T> valueType) {
    				if (segmentAccessor == accessor) {
    					return (T) Reflections.newInstance(embeddedType);
    				} else if (segmentAccessor == collectionAccessor){
    					if (collectionFactory != null) {
    						return (T) collectionFactory.get();
    					} else {
    						return super.newInstance(segmentAccessor, valueType);
    					}
    				} else {
    					return super.newInstance(segmentAccessor, valueType);
    				}
    			}
    		});
    		ShiftedMappedByConfiguration<E, SRC, TRGT, C2> shiftedMappedByConfiguration = this.mappedByConfiguration.embedInto(accessor);

    		ManyToManyRelation<E, TRGT, TRGTID, C1, S> result = new ManyToManyRelation<>(new ReadWriteAccessorChain<>(shiftedTargetProvider),
    				this::isSourceTablePerClassPolymorphic,
    				this.targetMappingConfiguration,
    				shiftedMappedByConfiguration);
    		result.setRelationMode(this.getRelationMode());
    		result.setFetchSeparately(this.isFetchSeparately());
    		result.setIndexingColumnName(this.getIndexingColumnName());
    		result.setOrdered(this.isOrdered());
    		result.setCollectionFactory(this.getCollectionFactory());
    		return result;
    	}

    	public static class MappedByConfiguration<SRC, TRGT, C2 extends Collection<SRC>> {

    		/**
    		 * Combiner of target entity with source entity
    		 */
    		@Nullable
    		private SerializablePropertyMutator<TRGT, SRC> reverseCombiner;

    		/**
    		 * Source getter on target for bidirectionality (no consequence on database mapping).
    		 */
    		@Nullable
    		private SerializablePropertyAccessor<TRGT, C2> reverseCollectionAccessor;

    		/**
    		 * Source setter on target for bidirectionality (no consequence on database mapping).
    		 */
    		@Nullable
    		private SerializablePropertyMutator<TRGT, C2> reverseCollectionMutator;

    		/** Optional provider of collection instance to be used if collection value is null */
    		@Nullable
    		private Supplier<C2> reverseCollectionFactory;

    		@Nullable
    		protected String associationTableName;

    		@Nullable
    		protected String sourceJoinColumnName;

    		@Nullable
    		protected String targetJoinColumnName;

    		@Nullable
    		public SerializablePropertyMutator<TRGT, SRC> getReverseCombiner() {
    			return reverseCombiner;
    		}

    		public void setReverseCombiner(@Nullable SerializablePropertyMutator<TRGT, SRC> reverseCombiner) {
    			this.reverseCombiner = reverseCombiner;
    		}

    		@Nullable
    		public SerializablePropertyAccessor<TRGT, C2> getReverseCollectionAccessor() {
    			return reverseCollectionAccessor;
    		}

    		public void setReverseCollectionAccessor(@Nullable SerializablePropertyAccessor<TRGT, C2> reverseCollectionAccessor) {
    			this.reverseCollectionAccessor = reverseCollectionAccessor;
    		}

    		@Nullable
    		public SerializablePropertyMutator<TRGT, C2> getReverseCollectionMutator() {
    			return reverseCollectionMutator;
    		}

    		public void setReverseCollectionMutator(@Nullable SerializablePropertyMutator<TRGT, C2> reverseCollectionMutator) {
    			this.reverseCollectionMutator = reverseCollectionMutator;
    		}

    		@Nullable
    		public Supplier<C2> getReverseCollectionFactory() {
    			return reverseCollectionFactory;
    		}

    		public void setReverseCollectionFactory(@Nullable Supplier<C2> reverseCollectionFactory) {
    			this.reverseCollectionFactory = reverseCollectionFactory;
    		}

    		@Nullable
    		public String getAssociationTableName() {
    			return associationTableName;
    		}

    		public void setAssociationTableName(@Nullable String associationTableName) {
    			this.associationTableName = associationTableName;
    		}

    		@Nullable
    		public String getSourceJoinColumnName() {
    			return sourceJoinColumnName;
    		}

    		public void setSourceJoinColumnName(@Nullable String sourceJoinColumnName) {
    			this.sourceJoinColumnName = sourceJoinColumnName;
    		}

    		@Nullable
    		public String getTargetJoinColumnName() {
    			return targetJoinColumnName;
    		}

    		public void setTargetJoinColumnName(@Nullable String targetJoinColumnName) {
    			this.targetJoinColumnName = targetJoinColumnName;
    		}

    		public boolean isEmpty() {
    			return reverseCollectionAccessor == null && reverseCollectionMutator == null && reverseCollectionFactory == null && reverseCombiner == null;
    		}

    		<C> ShiftedMappedByConfiguration<C, SRC, TRGT, C2> embedInto(Accessor<C, SRC> accessor) {
    			return new ShiftedMappedByConfiguration<>(accessor, this);
    		}
    	}

    	public static class ShiftedMappedByConfiguration<C, SRC, TRGT, C2 extends Collection<SRC>> extends MappedByConfiguration<SRC, TRGT, C2> {

    		private final Accessor<C, SRC> shifter;

    		private ShiftedMappedByConfiguration(Accessor<C, SRC> shifter, MappedByConfiguration<SRC, TRGT, C2> mappedByConfiguration) {
    			setReverseCombiner(mappedByConfiguration.getReverseCombiner());
    			setReverseCollectionAccessor(mappedByConfiguration.getReverseCollectionAccessor());
    			setReverseCollectionMutator(mappedByConfiguration.getReverseCollectionMutator());
    			setReverseCollectionFactory(mappedByConfiguration.getReverseCollectionFactory());
    			this.shifter = shifter;
    		}

    		public Accessor<C, SRC> getShifter() {
    			return shifter;
    		}
    	}
    }