/*
  Copyright (c) 2007, 2014, Oracle and/or its affiliates. All rights reserved.

  The MySQL Connector/J is licensed under the terms of the GPLv2
  <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
  There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
  this software, see the FOSS License Exception
  <http://www.mysql.com/about/legal/licensing/foss-exception.html>.

  This program is free software; you can redistribute it and/or modify it under the terms
  of the GNU General Public License as published by the Free Software Foundation; version 2
  of the License.

  This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  See the GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along with this
  program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
  Floor, Boston, MA 02110-1301  USA

 */

package com.mysql.jdbc;

import java.sql.SQLException;
import java.util.Properties;

/**
 * Implement this interface to be placed "in between" query execution, so that you can influence it. (currently experimental).
 * 
 * StatementInterceptors are "chainable" when configured by the user, the results returned by the "current" interceptor will be passed on to the next on in the
 * chain, from left-to-right order, as specified by the user in the JDBC configuration property "statementInterceptors".
 */

public interface StatementInterceptor extends Extension {

    /**
     * Called once per connection that wants to use the interceptor
     * 
     * The properties are the same ones passed in in the URL or arguments to
     * Driver.connect() or DriverManager.getConnection().
     * 
     * @param conn
     *            the connection for which this interceptor is being created
     * @param props
     *            configuration values as passed to the connection. Note that
     *            in order to support javax.sql.DataSources, configuration properties specific
     *            to an interceptor <strong>must</strong> be passed via setURL() on the
     *            DataSource. StatementInterceptor properties are not exposed via
     *            accessor/mutator methods on DataSources.
     * 
     * @throws SQLException
     *             should be thrown if the the StatementInterceptor
     *             can not initialize itself.
     */

    public abstract void init(Connection conn, Properties props) throws SQLException;

    /**
     * Called before the given statement is going to be sent to the
     * server for processing.
     * 
     * Interceptors are free to return a result set (which must implement the
     * interface com.mysql.jdbc.ResultSetInternalMethods), and if so,
     * the server will not execute the query, and the given result set will be
     * returned to the application instead.
     * 
     * This method will be called while the connection-level mutex is held, so
     * it will only be called from one thread at a time.
     * 
     * @param sql
     *            the SQL representation of the statement
     * @param interceptedStatement
     *            the actual statement instance being intercepted
     * @param connection
     *            the connection the statement is using (passed in to make
     *            thread-safe implementations straightforward)
     * 
     * @return a result set that should be returned to the application instead
     *         of results that are created from actual execution of the intercepted
     *         statement.
     * 
     * @throws SQLException
     *             if an error occurs during execution
     * 
     * @see com.mysql.jdbc.ResultSetInternalMethods
     */

    public abstract ResultSetInternalMethods preProcess(String sql, Statement interceptedStatement, Connection connection) throws SQLException;

    /**
     * Called after the given statement has been sent to the server
     * for processing.
     * 
     * Interceptors are free to inspect the "original" result set, and if a
     * different result set is returned by the interceptor, it is used in place
     * of the "original" result set. (the result set returned by the interceptor
     * must implement the interface
     * com.mysql.jdbc.ResultSetInternalMethods).
     * 
     * This method will be called while the connection-level mutex is held, so
     * it will only be called from one thread at a time.
     * 
     * @param sql
     *            the SQL representation of the statement
     * @param interceptedStatement
     *            the actual statement instance being intercepted
     * @param connection
     *            the connection the statement is using (passed in to make
     *            thread-safe implementations straightforward)
     * 
     * @return a result set that should be returned to the application instead
     *         of results that are created from actual execution of the intercepted
     *         statement.
     * 
     * @throws SQLException
     *             if an error occurs during execution
     * 
     * @see com.mysql.jdbc.ResultSetInternalMethods
     */
    public abstract ResultSetInternalMethods postProcess(String sql, Statement interceptedStatement, ResultSetInternalMethods originalResultSet,
            Connection connection) throws SQLException;

    /**
     * Should the driver execute this interceptor only for the
     * "original" top-level query, and not put it in the execution
     * path for queries that may be executed from other interceptors?
     * 
     * If an interceptor issues queries using the connection it was created for,
     * and does not return <code>true</code> for this method, it must ensure
     * that it does not cause infinite recursion.
     * 
     * @return true if the driver should ensure that this interceptor is only
     *         executed for the top-level "original" query.
     */
    public abstract boolean executeTopLevelOnly();

    /**
     * Called by the driver when this extension should release any resources
     * it is holding and cleanup internally before the connection is
     * closed.
     */
    public abstract void destroy();
}