/*
 * Copyright 2002-2017 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.support.incrementer;

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

import org.springframework.dao.DataAccessException;
import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.jdbc.datasource.DataSourceUtils;
import org.springframework.jdbc.support.JdbcUtils;

/**
 * {@link DataFieldMaxValueIncrementer} that increments the maximum value of a given MySQL table
 * with the equivalent of an auto-increment column. Note: If you use this class, your MySQL
 * key column should <i>NOT</i> be auto-increment, as the sequence table does the job.
 *
 * <p>The sequence is kept in a table; there should be one sequence table per
 * table that needs an auto-generated key. The storage engine used by the sequence table
 * can be MYISAM or INNODB since the sequences are allocated using a separate connection
 * without being affected by any other transactions that might be in progress.
 *
 * <p>Example:
 *
 * <pre class="code">create table tab (id int unsigned not null primary key, text varchar(100));
 * create table tab_sequence (value int not null);
 * insert into tab_sequence values(0);</pre>
 *
 * If "cacheSize" is set, the intermediate values are served without querying the
 * database. If the server or your application is stopped or crashes or a transaction
 * is rolled back, the unused values will never be served. The maximum hole size in
 * numbering is consequently the value of cacheSize.
 *
 * <p>It is possible to avoid acquiring a new connection for the incrementer by setting the
 * "useNewConnection" property to false. In this case you <i>MUST</i> use a non-transactional
 * storage engine like MYISAM when defining the incrementer table.
 *
 * @author Jean-Pierre Pawlak
 * @author Thomas Risberg
 * @author Juergen Hoeller
 */
public class MySQLMaxValueIncrementer extends AbstractColumnMaxValueIncrementer {

        /** The SQL string for retrieving the new sequence value */
        private static final String VALUE_SQL = "select last_insert_id()";

        /** The next id to serve */
        private long nextId = 0;

        /** The max id to serve */
        private long maxId = 0;

        /** Whether or not to use a new connection for the incrementer */
        private boolean useNewConnection = false;


        /**
         * Default constructor for bean property style usage.
         * @see #setDataSource
         * @see #setIncrementerName
         * @see #setColumnName
         */
        public MySQLMaxValueIncrementer() {
        }

        /**
         * Convenience constructor.
         * @param dataSource the DataSource to use
         * @param incrementerName the name of the sequence table to use
         * @param columnName the name of the column in the sequence table to use
         */
        public MySQLMaxValueIncrementer(DataSource dataSource, String incrementerName, String columnName) {
                super(dataSource, incrementerName, columnName);
        }


        /**
         * Set whether to use a new connection for the incrementer.
         * <p>{@code true} is necessary to support transactional storage engines,
         * using an isolated separate transaction for the increment operation.
         * {@code false} is sufficient if the storage engine of the sequence table
         * is non-transactional (like MYISAM), avoiding the effort of acquiring an
         * extra {@code Connection} for the increment operation.
         * <p>Default is {@code false} in the Spring Framework 4.3.x line.
         * @since 4.3.6
         * @see DataSource#getConnection()
         */
        public void setUseNewConnection(boolean useNewConnection) {
                this.useNewConnection = useNewConnection;
        }


        @Override
        protected synchronized long getNextKey() throws DataAccessException {
                if (this.maxId == this.nextId) {
                        /*
                        * If useNewConnection is true, then we obtain a non-managed connection so our modifications
                        * are handled in a separate transaction. If it is false, then we use the current transaction's
                        * connection relying on the use of a non-transactional storage engine like MYISAM for the
                        * incrementer table. We also use straight JDBC code because we need to make sure that the insert
                        * and select are performed on the same connection (otherwise we can't be sure that last_insert_id()
                        * returned the correct value).
                        */
                        Connection con = null;
                        Statement stmt = null;
                        boolean mustRestoreAutoCommit = false;
                        try {
                                if (this.useNewConnection) {
                                        con = getDataSource().getConnection();
                                        if (con.getAutoCommit()) {
                                                mustRestoreAutoCommit = true;
                                                con.setAutoCommit(false);
                                        }
                                }
                                else {
                                        con = DataSourceUtils.getConnection(getDataSource());
                                }
                                stmt = con.createStatement();
                                if (!this.useNewConnection) {
                                        DataSourceUtils.applyTransactionTimeout(stmt, getDataSource());
                                }
                                // Increment the sequence column...
                                String columnName = getColumnName();
                                try {
                                        stmt.executeUpdate("update " + getIncrementerName() + " set " + columnName +
                                                        " = last_insert_id(" + columnName + " + " + getCacheSize() + ")");
                                }
                                catch (SQLException ex) {
                                        throw new DataAccessResourceFailureException("Could not increment " + columnName + " for " +
                                                        getIncrementerName() + " sequence table", ex);
                                }
                                // Retrieve the new max of the sequence column...
                                ResultSet rs = stmt.executeQuery(VALUE_SQL);
                                try {
                                        if (!rs.next()) {
                                                throw new DataAccessResourceFailureException("last_insert_id() failed after executing an update");
                                        }
                                        this.maxId = rs.getLong(1);
                                }
                                finally {
                                        JdbcUtils.closeResultSet(rs);
                                }
                                this.nextId = this.maxId - getCacheSize() + 1;
                        }
                        catch (SQLException ex) {
                                throw new DataAccessResourceFailureException("Could not obtain last_insert_id()", ex);
                        }
                        finally {
                                JdbcUtils.closeStatement(stmt);
                                if (con != null) {
                                        if (this.useNewConnection) {
                                                try {
                                                        con.commit();
                                                        if (mustRestoreAutoCommit) {
                                                                con.setAutoCommit(true);
                                                        }
                                                }
                                                catch (SQLException ignore) {
                                                        throw new DataAccessResourceFailureException(
                                                                        "Unable to commit new sequence value changes for " + getIncrementerName());
                                                }
                                                JdbcUtils.closeConnection(con);
                                        }
                                        else {
                                                DataSourceUtils.releaseConnection(con, getDataSource());
                                        }
                                }
                        }
                }
                else {
                        this.nextId++;
                }
                return this.nextId;
        }

}