# IdentifierManagerStep.java

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

    import java.util.function.Function;

    import org.codefilarete.reflection.AccessorDefinition;
    import org.codefilarete.reflection.ReadWritePropertyAccessPoint;
    import org.codefilarete.stalactite.dsl.MappingConfigurationException;
    import org.codefilarete.stalactite.dsl.idpolicy.AlreadyAssignedIdentifierPolicy;
    import org.codefilarete.stalactite.dsl.idpolicy.BeforeInsertIdentifierPolicy;
    import org.codefilarete.stalactite.dsl.idpolicy.BeforeInsertIdentifierPolicySupport;
    import org.codefilarete.stalactite.dsl.idpolicy.DatabaseSequenceIdentifierPolicySupport;
    import org.codefilarete.stalactite.dsl.idpolicy.GeneratedKeysPolicy;
    import org.codefilarete.stalactite.dsl.idpolicy.IdentifierPolicy;
    import org.codefilarete.stalactite.dsl.idpolicy.PooledHiLoSequenceIdentifierPolicySupport;
    import org.codefilarete.stalactite.engine.SeparateTransactionExecutor;
    import org.codefilarete.stalactite.engine.configurer.AbstractIdentification;
    import org.codefilarete.stalactite.engine.configurer.AbstractIdentification.CompositeKeyIdentification;
    import org.codefilarete.stalactite.engine.configurer.AbstractIdentification.SingleColumnIdentification;
    import org.codefilarete.stalactite.engine.configurer.builder.InheritanceMappingStep.MappingPerTable;
    import org.codefilarete.stalactite.mapping.AccessorWrapperIdAccessor;
    import org.codefilarete.stalactite.mapping.id.manager.AlreadyAssignedIdentifierManager;
    import org.codefilarete.stalactite.mapping.id.manager.BeforeInsertIdentifierManager;
    import org.codefilarete.stalactite.mapping.id.manager.IdentifierInsertionManager;
    import org.codefilarete.stalactite.mapping.id.manager.JDBCGeneratedKeysIdentifierManager;
    import org.codefilarete.stalactite.mapping.id.sequence.hilo.PooledHiLoSequence;
    import org.codefilarete.stalactite.mapping.id.sequence.hilo.PooledHiLoSequenceOptions;
    import org.codefilarete.stalactite.mapping.id.sequence.hilo.PooledHiLoSequencePersister;
    import org.codefilarete.stalactite.sql.ConnectionConfiguration;
    import org.codefilarete.stalactite.sql.ConnectionProvider;
    import org.codefilarete.stalactite.sql.Dialect;
    import org.codefilarete.stalactite.sql.ddl.structure.Column;
    import org.codefilarete.stalactite.sql.ddl.structure.Database;
    import org.codefilarete.stalactite.sql.ddl.structure.Database.Schema;
    import org.codefilarete.stalactite.sql.ddl.structure.Table;
    import org.codefilarete.tool.Reflections;
    import org.codefilarete.tool.function.Sequence;

    import static org.codefilarete.tool.Nullable.nullable;
    import static org.codefilarete.tool.Reflections.PRIMITIVE_DEFAULT_VALUES;
    import static org.codefilarete.tool.collection.Iterables.first;

    public class IdentifierManagerStep<C, I> extends AbstractIdentificationStep<C, I> {

    	void applyIdentifierManager(AbstractIdentification<C, I> identification,
    								MappingPerTable<C> inheritanceMappingPerTable,
    								ReadWritePropertyAccessPoint<C, I> idAccessor,
    								Dialect dialect,
    								ConnectionConfiguration connectionConfiguration) {
    		determineIdentifierManager(identification, inheritanceMappingPerTable, idAccessor, dialect, connectionConfiguration);
    	}

    	/**
    	 * Determines {@link IdentifierInsertionManager} for current configuration as well as its whole inheritance configuration.
    	 * The result is set in given {@link SingleColumnIdentification}. Could have been done on a separate object but it would have complicated some method
    	 * signature, and {@link SingleColumnIdentification} is a good place for it.
    	 *
    	 * @param identification given to know the expected policy and to set the result in it
    	 * @param mappingPerTable necessary to get table and primary key to be read in the after-insert policy
    	 * @param idAccessor id accessor to get and set identifier on entity (except for already-assigned strategy)
    	 * @param dialect dialect to compute elements of identifier policy
    	 */
    	private void determineIdentifierManager(AbstractIdentification<C, I> identification,
    											MappingPerTable<C> mappingPerTable,
    											ReadWritePropertyAccessPoint<C, I> idAccessor,
    											Dialect dialect,
    											ConnectionConfiguration connectionConfiguration) {
    		AccessorDefinition idDefinition = AccessorDefinition.giveDefinition(idAccessor);
    		Class<I> identifierType = idDefinition.getMemberType();
    		IdentifierInsertionManager<C, I> identifierInsertionManager = null;
    		if (identification instanceof AbstractIdentification.CompositeKeyIdentification) {
    			identifierInsertionManager = new AlreadyAssignedIdentifierManager<>(
    					identifierType,
    					((CompositeKeyIdentification<C, I>) identification).getMarkAsPersistedFunction(),
    					((CompositeKeyIdentification<C, I>) identification).getIsPersistedFunction());
    		} else {
    			IdentifierPolicy<I> identifierPolicy = ((SingleColumnIdentification<C, I>) identification).getIdentifierPolicy();
    			if (identifierPolicy instanceof GeneratedKeysPolicy) {
    				// with identifier set by database generated key, identifier must be retrieved as soon as possible which means by the very first
    				// persister, which is current one, which is the first in order of mappings
    				Table<?> targetTable = first(mappingPerTable.getMappings()).getTargetTable();
    				if (targetTable.getPrimaryKey().isComposed()) {
    					throw new UnsupportedOperationException("Composite primary key is not compatible with database-generated column");
    				}
    				Column<?, I> primaryKey = (Column<?, I>) first(targetTable.getPrimaryKey().getColumns());
    				identifierInsertionManager = new JDBCGeneratedKeysIdentifierManager<>(
    						new AccessorWrapperIdAccessor<>(idAccessor),
    						dialect.buildGeneratedKeysReader(primaryKey.getName(), primaryKey.getJavaType()),
    						primaryKey.getJavaType()
    				);
    			} else if (identifierPolicy instanceof BeforeInsertIdentifierPolicy) {
    				Sequence<I> sequence;
    				if (identifierPolicy instanceof PooledHiLoSequenceIdentifierPolicySupport) {
    					Class<C> entityType = identification.getIdentificationDefiner().getEntityType();
    					PooledHiLoSequenceOptions options = new PooledHiLoSequenceOptions(50, entityType.getSimpleName());
    					ConnectionProvider connectionProvider = connectionConfiguration.getConnectionProvider();
    					if (!(connectionProvider instanceof SeparateTransactionExecutor)) {
    						throw new MappingConfigurationException("Before-insert identifier policy configured with connection that doesn't support separate transaction,"
    								+ " please provide a " + Reflections.toString(SeparateTransactionExecutor.class) + " as connection provider or change identifier policy");
    					}
    					sequence = (Sequence<I>) new PooledHiLoSequence(options,
    							new PooledHiLoSequencePersister(((PooledHiLoSequenceIdentifierPolicySupport) identifierPolicy).getStorageOptions(), dialect, (SeparateTransactionExecutor) connectionProvider, connectionConfiguration.getBatchSize()));
    				} else if (identifierPolicy instanceof DatabaseSequenceIdentifierPolicySupport) {
    					Class<C> entityType = identification.getIdentificationDefiner().getEntityType();
    					DatabaseSequenceIdentifierPolicySupport databaseSequenceSupport = (DatabaseSequenceIdentifierPolicySupport) identifierPolicy;
    					String sequenceName = databaseSequenceSupport.getDatabaseSequenceNamingStrategy().giveName(entityType);
    					Database database = new Database();
    					Schema sequenceSchema = nullable(databaseSequenceSupport.getDatabaseSequenceSettings().getSchemaName())
    							.map(s -> database.new Schema(s))
    							.elseSet(() -> first(mappingPerTable.getMappings()).getTargetTable().getSchema())
    							.get();
    					org.codefilarete.stalactite.sql.ddl.structure.Sequence databaseSequence
    							= new org.codefilarete.stalactite.sql.ddl.structure.Sequence(sequenceSchema, sequenceName)
    							.withBatchSize(databaseSequenceSupport.getDatabaseSequenceSettings().getBatchSize())
    							.withInitialValue(databaseSequenceSupport.getDatabaseSequenceSettings().getInitialValue());
    					sequence = (Sequence<I>) dialect.getDatabaseSequenceSelectorFactory().create(databaseSequence, connectionConfiguration.getConnectionProvider());
    				} else if (identifierPolicy instanceof BeforeInsertIdentifierPolicySupport) {
    					sequence = ((BeforeInsertIdentifierPolicySupport<I>) identifierPolicy).getSequence();
    				} else {
    					throw new MappingConfigurationException("Before-insert identifier policy " + Reflections.toString(identifierPolicy.getClass()) + " is not supported");
    				}
    				identifierInsertionManager = new BeforeInsertIdentifierManager<>(new AccessorWrapperIdAccessor<>(idAccessor), sequence, identifierType);
    			} else if (identifierPolicy instanceof AlreadyAssignedIdentifierPolicy) {
    				AlreadyAssignedIdentifierPolicy<C, I> alreadyAssignedPolicy = (AlreadyAssignedIdentifierPolicy<C, I>) identifierPolicy;
    				identifierInsertionManager = new AlreadyAssignedIdentifierManager<>(
    						identifierType,
    						alreadyAssignedPolicy.getMarkAsPersistedFunction(),
    						alreadyAssignedPolicy.getIsPersistedFunction());
    			}
    		}

    		// Treating configurations that are not the identifying one (for child-class) : they get an already-assigned identifier manager
    		AlreadyAssignedIdentifierManager<C, I> fallbackMappingIdentifierManager = determineFallbackIdentifierManager(idAccessor, identifierInsertionManager, identifierType);
    		identification
    				.setInsertionManager(identifierInsertionManager)
    				.setFallbackInsertionManager(fallbackMappingIdentifierManager);
    	}

    	private <E> AlreadyAssignedIdentifierManager<E, I> determineFallbackIdentifierManager(ReadWritePropertyAccessPoint<E, I> idAccessor,
    																						  IdentifierInsertionManager<E, I> identifierInsertionManager,
    																						  Class<I> identifierType) {
    		AlreadyAssignedIdentifierManager<E, I> fallbackMappingIdentifierManager;
    		if (identifierInsertionManager instanceof AlreadyAssignedIdentifierManager) {
    			fallbackMappingIdentifierManager = new AlreadyAssignedIdentifierManager<>(identifierType,
    					((AlreadyAssignedIdentifierManager<E, I>) identifierInsertionManager).getMarkAsPersistedFunction(),
    					((AlreadyAssignedIdentifierManager<E, I>) identifierInsertionManager).getIsPersistedFunction());
    		} else {
    			// auto-increment, sequence, etc : non-identifying classes get an already-assigned identifier manager based on their default value
    			Function<E, Boolean> isPersistedFunction = identifierType.isPrimitive()
    					? c -> PRIMITIVE_DEFAULT_VALUES.get(identifierType) == idAccessor.get(c)
    					: c -> idAccessor.get(c) != null;
    			fallbackMappingIdentifierManager = new AlreadyAssignedIdentifierManager<>(identifierType, c -> {}, isPersistedFunction);
    		}
    		return fallbackMappingIdentifierManager;
    	}
    }