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 *   Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you 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
 *
 *    http://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.
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package org.apache.cayenne.dba.mysql;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Collections;

import org.apache.cayenne.access.DataNode;
import org.apache.cayenne.dba.JdbcAdapter;
import org.apache.cayenne.dba.JdbcPkGenerator;
import org.apache.cayenne.map.DbEntity;
import org.apache.cayenne.tx.BaseTransaction;
import org.apache.cayenne.tx.Transaction;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 */
public class MySQLPkGenerator extends JdbcPkGenerator {

	private static final Logger logger = LoggerFactory.getLogger(MySQLPkGenerator.class);

	MySQLPkGenerator(JdbcAdapter adapter) {
		super(adapter);
	}

	/**
	 * Overrides superclass's implementation to perform locking of the primary
	 * key lookup table.
	 * 
	 * @since 3.0
	 */
	@Override
	protected long longPkFromDatabase(DataNode node, DbEntity entity) throws Exception {

		// must work directly with JDBC connection, since we
		// must unlock the AUTO_PK_SUPPORT table in case of
		// failures.... ah..JDBC is fun...

		// chained SQL exception
		SQLException exception = null;
		long pk = -1L;

		// Start new transaction if needed, can any way lead to problems when
		// using external transaction manager. We can only warn about it.
		// See https://issues.apache.org/jira/browse/CAY-2186 for details.
		Transaction transaction = BaseTransaction.getThreadTransaction();
		if(transaction != null && transaction.isExternal()) {
			logger.warn("Using MysqlPkGenerator with external transaction manager may lead to inconsistent state.");
		}
		BaseTransaction.bindThreadTransaction(null);

		try (Connection con = node.getDataSource().getConnection()) {

			if (con.getAutoCommit()) {
				con.setAutoCommit(false);
			}

			try(Statement st = con.createStatement()) {
				try {
					pk = getLongPrimaryKey(st, entity.getName());
					con.commit();
				} catch (SQLException pkEx) {
					try {
						con.rollback();
					} catch (SQLException ignored) {
					}

					exception = processSQLException(pkEx, null);
				} finally {
					// UNLOCK!
					// THIS MUST BE EXECUTED NO MATTER WHAT, OR WE WILL LOCK THE PRIMARY KEY TABLE!!
					try {
						String unlockString = "UNLOCK TABLES";
						adapter.getJdbcEventLogger().log(unlockString);
						st.execute(unlockString);
					} catch (SQLException unlockEx) {
						exception = processSQLException(unlockEx, exception);
					}
				}
			}
		} catch (SQLException otherEx) {
			exception = processSQLException(otherEx, null);
		} finally {
			BaseTransaction.bindThreadTransaction(transaction);
		}

		// check errors
		if (exception != null) {
			throw exception;
		}

		return pk;

	}

	/**
	 * Appends a new SQLException to the chain. If parent is null, uses the
	 * exception as the chain root.
	 */
	protected SQLException processSQLException(SQLException exception, SQLException parent) {
		if (parent == null) {
			return exception;
		}

		parent.setNextException(exception);
		return parent;
	}

	@Override
	protected String dropAutoPkString() {
		return "DROP TABLE IF EXISTS AUTO_PK_SUPPORT";
	}

	@Override
	protected String pkTableCreateString() {
		return "CREATE TABLE IF NOT EXISTS AUTO_PK_SUPPORT " +
				"(TABLE_NAME CHAR(100) NOT NULL, NEXT_ID BIGINT NOT NULL, UNIQUE (TABLE_NAME)) " +
				"ENGINE=" + MySQLAdapter.DEFAULT_STORAGE_ENGINE;
	}

	/**
	 * @since 3.0
	 */
	protected long getLongPrimaryKey(Statement statement, String entityName) throws SQLException {
		// lock
		String lockString = "LOCK TABLES AUTO_PK_SUPPORT WRITE";
		adapter.getJdbcEventLogger().log(lockString);
		statement.execute(lockString);

		// select
		String selectString = super.pkSelectString(entityName);
		adapter.getJdbcEventLogger().log(selectString);
		long pk;
		try(ResultSet rs = statement.executeQuery(selectString)) {
			if (!rs.next()) {
				throw new SQLException("No rows for '" + entityName + "'");
			}

			pk = rs.getLong(1);
			if (rs.next()) {
				throw new SQLException("More than one row for '" + entityName + "'");
			}
		}

		// update
		String updateString = super.pkUpdateString(entityName) + " AND NEXT_ID = " + pk;
		adapter.getJdbcEventLogger().log(updateString);
		int updated = statement.executeUpdate(updateString);
		// optimistic lock failure...
		if (updated != 1) {
			throw new SQLException("Error updating PK count '" + entityName + "': " + updated);
		}

		return pk;
	}
}