/*
 * Copyright 2002-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.jdbc.datasource;

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import javax.sql.DataSource;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.transaction.CannotCreateTransactionException;
import org.springframework.transaction.TransactionDefinition;
import org.springframework.transaction.TransactionSystemException;
import org.springframework.transaction.support.AbstractPlatformTransactionManager;
import org.springframework.transaction.support.DefaultTransactionStatus;
import org.springframework.transaction.support.ResourceTransactionManager;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.transaction.support.TransactionSynchronizationUtils;

/**
 * {@link org.springframework.transaction.PlatformTransactionManager}
 * implementation for a single JDBC {@link javax.sql.DataSource}. This class is
 * capable of working in any environment with any JDBC driver, as long as the setup
 * uses a {@code javax.sql.DataSource} as its {@code Connection} factory mechanism.
 * Binds a JDBC Connection from the specified DataSource to the current thread,
 * potentially allowing for one thread-bound Connection per DataSource.
 *
 * <p><b>Note: The DataSource that this transaction manager operates on needs
 * to return independent Connections.</b> The Connections may come from a pool
 * (the typical case), but the DataSource must not return thread-scoped /
 * request-scoped Connections or the like. This transaction manager will
 * associate Connections with thread-bound transactions itself, according
 * to the specified propagation behavior. It assumes that a separate,
 * independent Connection can be obtained even during an ongoing transaction.
 *
 * <p>Application code is required to retrieve the JDBC Connection via
 * {@link DataSourceUtils#getConnection(DataSource)} instead of a standard
 * Java EE-style {@link DataSource#getConnection()} call. Spring classes such as
 * {@link org.springframework.jdbc.core.JdbcTemplate} use this strategy implicitly.
 * If not used in combination with this transaction manager, the
 * {@link DataSourceUtils} lookup strategy behaves exactly like the native
 * DataSource lookup; it can thus be used in a portable fashion.
 *
 * <p>Alternatively, you can allow application code to work with the standard
 * Java EE-style lookup pattern {@link DataSource#getConnection()}, for example for
 * legacy code that is not aware of Spring at all. In that case, define a
 * {@link TransactionAwareDataSourceProxy} for your target DataSource, and pass
 * that proxy DataSource to your DAOs, which will automatically participate in
 * Spring-managed transactions when accessing it.
 *
 * <p>Supports custom isolation levels, and timeouts which get applied as
 * appropriate JDBC statement timeouts. To support the latter, application code
 * must either use {@link org.springframework.jdbc.core.JdbcTemplate}, call
 * {@link DataSourceUtils#applyTransactionTimeout} for each created JDBC Statement,
 * or go through a {@link TransactionAwareDataSourceProxy} which will create
 * timeout-aware JDBC Connections and Statements automatically.
 *
 * <p>Consider defining a {@link LazyConnectionDataSourceProxy} for your target
 * DataSource, pointing both this transaction manager and your DAOs to it.
 * This will lead to optimized handling of "empty" transactions, i.e. of transactions
 * without any JDBC statements executed. A LazyConnectionDataSourceProxy will not fetch
 * an actual JDBC Connection from the target DataSource until a Statement gets executed,
 * lazily applying the specified transaction settings to the target Connection.
 *
 * <p>This transaction manager supports nested transactions via the JDBC 3.0
 * {@link java.sql.Savepoint} mechanism. The
 * {@link #setNestedTransactionAllowed "nestedTransactionAllowed"} flag defaults
 * to "true", since nested transactions will work without restrictions on JDBC
 * drivers that support savepoints (such as the Oracle JDBC driver).
 *
 * <p>This transaction manager can be used as a replacement for the
 * {@link org.springframework.transaction.jta.JtaTransactionManager} in the single
 * resource case, as it does not require a container that supports JTA, typically
 * in combination with a locally defined JDBC DataSource (e.g. an Apache Commons
 * DBCP connection pool). Switching between this local strategy and a JTA
 * environment is just a matter of configuration!
 *
 * <p>As of 4.3.4, this transaction manager triggers flush callbacks on registered
 * transaction synchronizations (if synchronization is generally active), assuming
 * resources operating on the underlying JDBC {@code Connection}. This allows for
 * setup analogous to {@code JtaTransactionManager}, in particular with respect to
 * lazily registered ORM resources (e.g. a Hibernate {@code Session}).
 *
 * @author Juergen Hoeller
 * @since 02.05.2003
 * @see #setNestedTransactionAllowed
 * @see java.sql.Savepoint
 * @see DataSourceUtils#getConnection(javax.sql.DataSource)
 * @see DataSourceUtils#applyTransactionTimeout
 * @see DataSourceUtils#releaseConnection
 * @see TransactionAwareDataSourceProxy
 * @see LazyConnectionDataSourceProxy
 * @see org.springframework.jdbc.core.JdbcTemplate
 */
@SuppressWarnings("serial")
public class DataSourceTransactionManager extends AbstractPlatformTransactionManager
                implements ResourceTransactionManager, InitializingBean {

        private DataSource dataSource;

        private boolean enforceReadOnly = false;


        /**
         * Create a new DataSourceTransactionManager instance.
         * A DataSource has to be set to be able to use it.
         * @see #setDataSource
         */
        public DataSourceTransactionManager() {
                setNestedTransactionAllowed(true);
        }

        /**
         * Create a new DataSourceTransactionManager instance.
         * @param dataSource the JDBC DataSource to manage transactions for
         */
        public DataSourceTransactionManager(DataSource dataSource) {
                this();
                setDataSource(dataSource);
                afterPropertiesSet();
        }


        /**
         * Set the JDBC DataSource that this instance should manage transactions for.
         * <p>This will typically be a locally defined DataSource, for example an
         * Apache Commons DBCP connection pool. Alternatively, you can also drive
         * transactions for a non-XA J2EE DataSource fetched from JNDI. For an XA
         * DataSource, use JtaTransactionManager.
         * <p>The DataSource specified here should be the target DataSource to manage
         * transactions for, not a TransactionAwareDataSourceProxy. Only data access
         * code may work with TransactionAwareDataSourceProxy, while the transaction
         * manager needs to work on the underlying target DataSource. If there's
         * nevertheless a TransactionAwareDataSourceProxy passed in, it will be
         * unwrapped to extract its target DataSource.
         * <p><b>The DataSource passed in here needs to return independent Connections.</b>
         * The Connections may come from a pool (the typical case), but the DataSource
         * must not return thread-scoped / request-scoped Connections or the like.
         * @see TransactionAwareDataSourceProxy
         * @see org.springframework.transaction.jta.JtaTransactionManager
         */
        public void setDataSource(DataSource dataSource) {
                if (dataSource instanceof TransactionAwareDataSourceProxy) {
                        // If we got a TransactionAwareDataSourceProxy, we need to perform transactions
                        // for its underlying target DataSource, else data access code won't see
                        // properly exposed transactions (i.e. transactions for the target DataSource).
                        this.dataSource = ((TransactionAwareDataSourceProxy) dataSource).getTargetDataSource();
                }
                else {
                        this.dataSource = dataSource;
                }
        }

        /**
         * Return the JDBC DataSource that this instance manages transactions for.
         */
        public DataSource getDataSource() {
                return this.dataSource;
        }

        /**
         * Specify whether to enforce the read-only nature of a transaction
         * (as indicated by {@link TransactionDefinition#isReadOnly()}
         * through an explicit statement on the transactional connection:
         * "SET TRANSACTION READ ONLY" as understood by Oracle, MySQL and Postgres.
         * <p>The exact treatment, including any SQL statement executed on the connection,
         * can be customized through {@link #prepareTransactionalConnection}.
         * <p>This mode of read-only handling goes beyond the {@link Connection#setReadOnly}
         * hint that Spring applies by default. In contrast to that standard JDBC hint,
         * "SET TRANSACTION READ ONLY" enforces an isolation-level-like connection mode
         * where data manipulation statements are strictly disallowed. Also, on Oracle,
         * this read-only mode provides read consistency for the entire transaction.
         * <p>Note that older Oracle JDBC drivers (9i, 10g) used to enforce this read-only
         * mode even for {@code Connection.setReadOnly(true}. However, with recent drivers,
         * this strong enforcement needs to be applied explicitly, e.g. through this flag.
         * @since 4.3.7
         * @see #prepareTransactionalConnection
         */
        public void setEnforceReadOnly(boolean enforceReadOnly) {
                this.enforceReadOnly = enforceReadOnly;
        }

        /**
         * Return whether to enforce the read-only nature of a transaction
         * through an explicit statement on the transactional connection.
         * @since 4.3.7
         * @see #setEnforceReadOnly
         */
        public boolean isEnforceReadOnly() {
                return this.enforceReadOnly;
        }

        @Override
        public void afterPropertiesSet() {
                if (getDataSource() == null) {
                        throw new IllegalArgumentException("Property 'dataSource' is required");
                }
        }


        @Override
        public Object getResourceFactory() {
                return getDataSource();
        }

        @Override
        protected Object doGetTransaction() {
                DataSourceTransactionObject txObject = new DataSourceTransactionObject();
                txObject.setSavepointAllowed(isNestedTransactionAllowed());
                ConnectionHolder conHolder =
                                (ConnectionHolder) TransactionSynchronizationManager.getResource(this.dataSource);
                txObject.setConnectionHolder(conHolder, false);
                return txObject;
        }

        @Override
        protected boolean isExistingTransaction(Object transaction) {
                DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
                return (txObject.hasConnectionHolder() && txObject.getConnectionHolder().isTransactionActive());
        }

        @Override
        protected void doBegin(Object transaction, TransactionDefinition definition) {
                DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
                Connection con = null;

                try {
                        if (!txObject.hasConnectionHolder() ||
                                        txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
                                Connection newCon = this.dataSource.getConnection();
                                if (logger.isDebugEnabled()) {
                                        logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
                                }
                                txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
                        }

                        txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
                        con = txObject.getConnectionHolder().getConnection();

                        Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
                        txObject.setPreviousIsolationLevel(previousIsolationLevel);

                        // Switch to manual commit if necessary. This is very expensive in some JDBC drivers,
                        // so we don't want to do it unnecessarily (for example if we've explicitly
                        // configured the connection pool to set it already).
                        if (con.getAutoCommit()) {
                                txObject.setMustRestoreAutoCommit(true);
                                if (logger.isDebugEnabled()) {
                                        logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
                                }
                                con.setAutoCommit(false);
                        }

                        prepareTransactionalConnection(con, definition);
                        txObject.getConnectionHolder().setTransactionActive(true);

                        int timeout = determineTimeout(definition);
                        if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
                                txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
                        }

                        // Bind the connection holder to the thread.
                        if (txObject.isNewConnectionHolder()) {
                                TransactionSynchronizationManager.bindResource(getDataSource(), txObject.getConnectionHolder());
                        }
                }

                catch (Throwable ex) {
                        if (txObject.isNewConnectionHolder()) {
                                DataSourceUtils.releaseConnection(con, this.dataSource);
                                txObject.setConnectionHolder(null, false);
                        }
                        throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
                }
        }

        @Override
        protected Object doSuspend(Object transaction) {
                DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
                txObject.setConnectionHolder(null);
                return TransactionSynchronizationManager.unbindResource(this.dataSource);
        }

        @Override
        protected void doResume(Object transaction, Object suspendedResources) {
                TransactionSynchronizationManager.bindResource(this.dataSource, suspendedResources);
        }

        @Override
        protected void doCommit(DefaultTransactionStatus status) {
                DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
                Connection con = txObject.getConnectionHolder().getConnection();
                if (status.isDebug()) {
                        logger.debug("Committing JDBC transaction on Connection [" + con + "]");
                }
                try {
                        con.commit();
                }
                catch (SQLException ex) {
                        throw new TransactionSystemException("Could not commit JDBC transaction", ex);
                }
        }

        @Override
        protected void doRollback(DefaultTransactionStatus status) {
                DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
                Connection con = txObject.getConnectionHolder().getConnection();
                if (status.isDebug()) {
                        logger.debug("Rolling back JDBC transaction on Connection [" + con + "]");
                }
                try {
                        con.rollback();
                }
                catch (SQLException ex) {
                        throw new TransactionSystemException("Could not roll back JDBC transaction", ex);
                }
        }

        @Override
        protected void doSetRollbackOnly(DefaultTransactionStatus status) {
                DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
                if (status.isDebug()) {
                        logger.debug("Setting JDBC transaction [" + txObject.getConnectionHolder().getConnection() +
                                        "] rollback-only");
                }
                txObject.setRollbackOnly();
        }

        @Override
        protected void doCleanupAfterCompletion(Object transaction) {
                DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;

                // Remove the connection holder from the thread, if exposed.
                if (txObject.isNewConnectionHolder()) {
                        TransactionSynchronizationManager.unbindResource(this.dataSource);
                }

                // Reset connection.
                Connection con = txObject.getConnectionHolder().getConnection();
                try {
                        if (txObject.isMustRestoreAutoCommit()) {
                                con.setAutoCommit(true);
                        }
                        DataSourceUtils.resetConnectionAfterTransaction(con, txObject.getPreviousIsolationLevel());
                }
                catch (Throwable ex) {
                        logger.debug("Could not reset JDBC Connection after transaction", ex);
                }

                if (txObject.isNewConnectionHolder()) {
                        if (logger.isDebugEnabled()) {
                                logger.debug("Releasing JDBC Connection [" + con + "] after transaction");
                        }
                        DataSourceUtils.releaseConnection(con, this.dataSource);
                }

                txObject.getConnectionHolder().clear();
        }


        /**
         * Prepare the transactional {@code Connection} right after transaction begin.
         * <p>The default implementation executes a "SET TRANSACTION READ ONLY" statement
         * if the {@link #setEnforceReadOnly "enforceReadOnly"} flag is set to {@code true}
         * and the transaction definition indicates a read-only transaction.
         * <p>The "SET TRANSACTION READ ONLY" is understood by Oracle, MySQL and Postgres
         * and may work with other databases as well. If you'd like to adapt this treatment,
         * override this method accordingly.
         * @param con the transactional JDBC Connection
         * @param definition the current transaction definition
         * @throws SQLException if thrown by JDBC API
         * @since 4.3.7
         * @see #setEnforceReadOnly
         */
        protected void prepareTransactionalConnection(Connection con, TransactionDefinition definition)
                        throws SQLException {

                if (isEnforceReadOnly() && definition.isReadOnly()) {
                        Statement stmt = con.createStatement();
                        try {
                                stmt.executeUpdate("SET TRANSACTION READ ONLY");
                        }
                        finally {
                                stmt.close();
                        }
                }
        }


        /**
         * DataSource transaction object, representing a ConnectionHolder.
         * Used as transaction object by DataSourceTransactionManager.
         */
        private static class DataSourceTransactionObject extends JdbcTransactionObjectSupport {

                private boolean newConnectionHolder;

                private boolean mustRestoreAutoCommit;

                public void setConnectionHolder(ConnectionHolder connectionHolder, boolean newConnectionHolder) {
                        super.setConnectionHolder(connectionHolder);
                        this.newConnectionHolder = newConnectionHolder;
                }

                public boolean isNewConnectionHolder() {
                        return this.newConnectionHolder;
                }

                public void setMustRestoreAutoCommit(boolean mustRestoreAutoCommit) {
                        this.mustRestoreAutoCommit = mustRestoreAutoCommit;
                }

                public boolean isMustRestoreAutoCommit() {
                        return this.mustRestoreAutoCommit;
                }

                public void setRollbackOnly() {
                        getConnectionHolder().setRollbackOnly();
                }

                @Override
                public boolean isRollbackOnly() {
                        return getConnectionHolder().isRollbackOnly();
                }

                @Override
                public void flush() {
                        if (TransactionSynchronizationManager.isSynchronizationActive()) {
                                TransactionSynchronizationUtils.triggerFlush();
                        }
                }
        }

}