/*
 * JBoss, Home of Professional Open Source.
 * Copyright 2006, Red Hat Middleware LLC, and individual contributors
 * as indicated by the @author tags. See the copyright.txt file in the
 * distribution for a full listing of individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.jboss.resource.adapter.jdbc.vendor;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.ResultSet;

import org.jboss.logging.Logger;
import org.jboss.resource.adapter.jdbc.ValidConnectionChecker;

/**
 * Implements sql connection validation check.
 * This should work on just about any version of the database,
 * but will use isValid() method with MSSQL JDBC driver 2.0 or later.
 * Prior to that version it just executes "SELECT 1" query.
 *
 * <p>Please note that the isValid() method requires java 6.
 *
 * <p>The code was inspired by MySQLValidConnectionChecker. See it's javadoc for
 * authors info. This code is released under the LGPL license.
 *
 @author Dmitry L (dmitryl att artezio dott com)
 */
public class MSSQLValidConnectionChecker implements ValidConnectionChecker, Serializable {

    private static transient Logger log;

    private static final String SQLSERVER_CONNECTION_CLASS = "com.microsoft.sqlserver.jdbc.SQLServerConnection";

    private static final String VALIDATION_SQL_QUERY = "SELECT 1";

    private transient boolean driverHasIsValidMethod;

    // The validation method
    private transient Method isValid;

    // The timeout for isValid method
    private static Object[] timeoutParam = new Object[]{1};

    private static final long serialVersionUID = 6563227959967309171L;


    public MSSQLValidConnectionChecker() {
	initIsValid();
    }

    public SQLException isValidConnection(Connection c) {
	// if there is a isValid method then use it
	if (driverHasIsValidMethod) {
	    try {
		Boolean valid = (Boolean) isValid.invoke(c, timeoutParam);
		if (!valid)
		    return new SQLException("Connection is unvalid or " + timeoutParam[0] + " sec timeout has expired");
	    }
	    catch (Exception e) {
		if (e instanceof SQLException) {
		    return (SQLException) e;
		} else {
		    log.warn("Unexpected error in isValid() method", e);
		    return new SQLException("isValid() method failed: " + e.toString());
		}
	    }
	    // otherwise just use a sql statement
	} else {
	    Statement stmt = null;
	    ResultSet rs = null;
	    try {
		stmt = c.createStatement();
		rs = stmt.executeQuery(VALIDATION_SQL_QUERY);
	    }
	    catch (Exception e) {
		if (e instanceof SQLException) {
		    return (SQLException) e;
		} else {
		    log.warn("Unexpected error in '" + VALIDATION_SQL_QUERY + "'", e);
		    return new SQLException("'" + VALIDATION_SQL_QUERY + "' failed: " + e.toString());
		}
	    }
	    finally {
		//cleanup the Statement
		try {
		    if (rs != null)
			rs.close();

		    if (stmt != null)
			stmt.close();
		}
		catch (SQLException ignore) {

		}
	    }
	}
	return null;
    }

    private void initIsValid() {
	log = Logger.getLogger(this.getClass());
	driverHasIsValidMethod = false;

	Class connectionClazz;
	try {
	    connectionClazz = Thread.currentThread().getContextClassLoader().loadClass(SQLSERVER_CONNECTION_CLASS);
	    isValid = connectionClazz.getMethod("isValid", new Class[]{int.class});
	    if (isValid != null) {
		driverHasIsValidMethod = true;
	    }
	} catch (ClassNotFoundException e) {
	    log.error("Cannot resolve " + SQLSERVER_CONNECTION_CLASS +
		" class. Wrong ValidConnectionChecker is configured?" +
		" Will use '" + VALIDATION_SQL_QUERY + "' instead.", e);

	} catch (SecurityException e) {
	    log.error("Cannot access " + SQLSERVER_CONNECTION_CLASS + ".isValid() " +
		"Will use '" + VALIDATION_SQL_QUERY + "' instead.", e);

	} catch (NoSuchMethodException e) {
/*
	    if (log.isDebugEnabled()) {
		log.debug("Cannot resolve isValid() method for " + SQLSERVER_CONNECTION_CLASS +
		    " class (JDBC driver 2.0+). Will use '" + VALIDATION_SQL_QUERY +
		    "' instead (JDBC driver 1.2 and earlier).", e);
	    }
*/
	    if (log.isDebugEnabled()) {
		log.debug("Cannot resolve isValid() method for " + SQLSERVER_CONNECTION_CLASS +
		    " class (JDBC driver 2.0+). Will use '" + VALIDATION_SQL_QUERY +
		    "' instead (JDBC driver 1.2 and earlier).");
	    }
	}
    }

    private void writeObject(ObjectOutputStream out) throws IOException {
	// really nothing to serialize - all fields are transient or initialized statically
	// out.defaultWriteObject();
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
	// really nothing to deserialize - all fields are transient or initialized statically
	// in.defaultReadObject();

	// reinitialize transient fields 
	initIsValid();
    }
}