<?php
/**
 * @package     Joomla.Platform
 * @subpackage  Database
 *
 * @copyright   Copyright (C) 2005 - 2018 Open Source Matters, Inc. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE
 */

defined('JPATH_PLATFORM') or die;

/**
 * SQL Server database driver
 *
 * @link   https://msdn.microsoft.com/en-us/library/cc296152(SQL.90).aspx
 * @since  12.1
 */
class JDatabaseDriverSqlsrv extends JDatabaseDriver
{
	/**
	 * The name of the database driver.
	 *
	 * @var    string
	 * @since  12.1
	 */
	public $name = 'sqlsrv';

	/**
	 * The type of the database server family supported by this driver.
	 *
	 * @var    string
	 * @since  CMS 3.5.0
	 */
	public $serverType = 'mssql';

	/**
	 * The character(s) used to quote SQL statement names such as table names or field names,
	 * etc.  The child classes should define this as necessary.  If a single character string the
	 * same character is used for both sides of the quoted name, else the first character will be
	 * used for the opening quote and the second for the closing quote.
	 *
	 * @var    string
	 * @since  12.1
	 */
	protected $nameQuote = '[]';

	/**
	 * The null or zero representation of a timestamp for the database driver.  This should be
	 * defined in child classes to hold the appropriate value for the engine.
	 *
	 * @var    string
	 * @since  12.1
	 */
	protected $nullDate = '1900-01-01 00:00:00';

	/**
	 * @var    string  The minimum supported database version.
	 * @since  12.1
	 */
	protected static $dbMinimum = '10.50.1600.1';

	/**
	 * Test to see if the SQLSRV connector is available.
	 *
	 * @return  boolean  True on success, false otherwise.
	 *
	 * @since   12.1
	 */
	public static function isSupported()
	{
		return function_exists('sqlsrv_connect');
	}

	/**
	 * Constructor.
	 *
	 * @param   array  $options  List of options used to configure the connection
	 *
	 * @since   12.1
	 */
	public function __construct($options)
	{
		// Get some basic values from the options.
		$options['host'] = (isset($options['host'])) ? $options['host'] : 'localhost';
		$options['user'] = (isset($options['user'])) ? $options['user'] : '';
		$options['password'] = (isset($options['password'])) ? $options['password'] : '';
		$options['database'] = (isset($options['database'])) ? $options['database'] : '';
		$options['select'] = (isset($options['select'])) ? (bool) $options['select'] : true;

		// Finalize initialisation
		parent::__construct($options);
	}

	/**
	 * Connects to the database if needed.
	 *
	 * @return  void  Returns void if the database connected successfully.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function connect()
	{
		if ($this->connection)
		{
			return;
		}

		// Build the connection configuration array.
		$config = array(
			'Database' => $this->options['database'],
			'uid' => $this->options['user'],
			'pwd' => $this->options['password'],
			'CharacterSet' => 'UTF-8',
			'ReturnDatesAsStrings' => true,
		);

		// Make sure the SQLSRV extension for PHP is installed and enabled.
		if (!self::isSupported())
		{
			throw new JDatabaseExceptionUnsupported('The sqlsrv extension for PHP is not installed or enabled..');
		}

		// Attempt to connect to the server.
		if (!($this->connection = @ sqlsrv_connect($this->options['host'], $config)))
		{
			throw new JDatabaseExceptionConnecting('Database sqlsrv_connect failed, ' . print_r(sqlsrv_errors(), true));
		}

		// Make sure that DB warnings are not returned as errors.
		sqlsrv_configure('WarningsReturnAsErrors', 0);

		// If auto-select is enabled select the given database.
		if ($this->options['select'] && !empty($this->options['database']))
		{
			$this->select($this->options['database']);
		}

		// Set charactersets.
		$this->utf = $this->setUtf();

		// Set QUOTED_IDENTIFIER always ON
		sqlsrv_query($this->connection, 'SET QUOTED_IDENTIFIER ON');
	}

	/**
	 * Disconnects the database.
	 *
	 * @return  void
	 *
	 * @since   12.1
	 */
	public function disconnect()
	{
		// Close the connection.
		if (is_resource($this->connection))
		{
			foreach ($this->disconnectHandlers as $h)
			{
				call_user_func_array($h, array( &$this));
			}

			sqlsrv_close($this->connection);
		}

		$this->connection = null;
	}

	/**
	 * Get table constraints
	 *
	 * @param   string  $tableName  The name of the database table.
	 *
	 * @return  array  Any constraints available for the table.
	 *
	 * @since   12.1
	 */
	protected function getTableConstraints($tableName)
	{
		$this->connect();

		$query = $this->getQuery(true);

		$this->setQuery(
			'SELECT CONSTRAINT_NAME FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE TABLE_NAME = ' . $query->quote($tableName)
		);

		return $this->loadColumn();
	}

	/**
	 * Rename constraints.
	 *
	 * @param   array   $constraints  Array(strings) of table constraints
	 * @param   string  $prefix       A string
	 * @param   string  $backup       A string
	 *
	 * @return  void
	 *
	 * @since   12.1
	 */
	protected function renameConstraints($constraints = array(), $prefix = null, $backup = null)
	{
		$this->connect();

		foreach ($constraints as $constraint)
		{
			$this->setQuery('sp_rename ' . $constraint . ',' . str_replace($prefix, $backup, $constraint));
			$this->execute();
		}
	}

	/**
	 * Method to escape a string for usage in an SQL statement.
	 *
	 * The escaping for MSSQL isn't handled in the driver though that would be nice.  Because of this we need
	 * to handle the escaping ourselves.
	 *
	 * @param   string   $text   The string to be escaped.
	 * @param   boolean  $extra  Optional parameter to provide extra escaping.
	 *
	 * @return  string  The escaped string.
	 *
	 * @since   12.1
	 */
	public function escape($text, $extra = false)
	{
		$result = str_replace("'", "''", $text);

		// SQL Server does not accept NULL byte in query string
		$result = str_replace("\0", "' + CHAR(0) + N'", $result);

		// Fix for SQL Server escape sequence, see https://support.microsoft.com/en-us/kb/164291
		$result = str_replace(
			array("\\\n",     "\\\r",     "\\\\\r\r\n"),
			array("\\\\\n\n", "\\\\\r\r", "\\\\\r\n\r\n"),
			$result
		);

		if ($extra)
		{
			// Escape special chars
			$result = str_replace(
				array('[',   '_',   '%'),
				array('[[]', '[_]', '[%]'),
				$result
			);
		}

		return $result;
	}

	/**
	 * Quotes and optionally escapes a string to database requirements for use in database queries.
	 *
	 * @param   mixed    $text    A string or an array of strings to quote.
	 * @param   boolean  $escape  True (default) to escape the string, false to leave it unchanged.
	 *
	 * @return  string  The quoted input string.
	 *
	 * @note    Accepting an array of strings was added in 12.3.
	 * @since   11.1
	 */
	public function quote($text, $escape = true)
	{
		if (is_array($text))
		{
			return parent::quote($text, $escape);
		}

		// To support unicode on MSSQL we have to add prefix N
		return 'N\'' . ($escape ? $this->escape($text) : $text) . '\'';
	}

	/**
	 * Determines if the connection to the server is active.
	 *
	 * @return  boolean  True if connected to the database engine.
	 *
	 * @since   12.1
	 */
	public function connected()
	{
		// TODO: Run a blank query here
		return true;
	}

	/**
	 * Drops a table from the database.
	 *
	 * @param   string   $tableName  The name of the database table to drop.
	 * @param   boolean  $ifExists   Optionally specify that the table must exist before it is dropped.
	 *
	 * @return  JDatabaseDriverSqlsrv  Returns this object to support chaining.
	 *
	 * @since   12.1
	 */
	public function dropTable($tableName, $ifExists = true)
	{
		$this->connect();

		$query = $this->getQuery(true);

		if ($ifExists)
		{
			$this->setQuery(
				'IF EXISTS(SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = ' . $query->quote($tableName) . ') DROP TABLE ' . $tableName
			);
		}
		else
		{
			$this->setQuery('DROP TABLE ' . $tableName);
		}

		$this->execute();

		return $this;
	}

	/**
	 * Get the number of affected rows for the previous executed SQL statement.
	 *
	 * @return  integer  The number of affected rows.
	 *
	 * @since   12.1
	 */
	public function getAffectedRows()
	{
		$this->connect();

		return sqlsrv_rows_affected($this->cursor);
	}

	/**
	 * Method to get the database collation in use by sampling a text field of a table in the database.
	 *
	 * @return  mixed  The collation in use by the database or boolean false if not supported.
	 *
	 * @since   12.1
	 */
	public function getCollation()
	{
		// TODO: Not fake this
		return 'MSSQL UTF-8 (UCS2)';
	}

	/**
	 * Method to get the database connection collation, as reported by the driver. If the connector doesn't support
	 * reporting this value please return an empty string.
	 *
	 * @return  string
	 */
	public function getConnectionCollation()
	{
		// TODO: Not fake this
		return 'MSSQL UTF-8 (UCS2)';
	}

	/**
	 * Get the number of returned rows for the previous executed SQL statement.
	 *
	 * @param   resource  $cursor  An optional database cursor resource to extract the row count from.
	 *
	 * @return  integer   The number of returned rows.
	 *
	 * @since   12.1
	 */
	public function getNumRows($cursor = null)
	{
		$this->connect();

		return sqlsrv_num_rows($cursor ? $cursor : $this->cursor);
	}

	/**
	 * Retrieves field information about the given tables.
	 *
	 * @param   mixed    $table     A table name
	 * @param   boolean  $typeOnly  True to only return field types.
	 *
	 * @return  array  An array of fields.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function getTableColumns($table, $typeOnly = true)
	{
		$result = array();

		$table_temp = $this->replacePrefix((string) $table);

		// Set the query to get the table fields statement.
		$this->setQuery(
			'SELECT column_name as Field, data_type as Type, is_nullable as \'Null\', column_default as \'Default\'' .
			' FROM information_schema.columns WHERE table_name = ' . $this->quote($table_temp)
		);
		$fields = $this->loadObjectList();

		// If we only want the type as the value add just that to the list.
		if ($typeOnly)
		{
			foreach ($fields as $field)
			{
				$result[$field->Field] = preg_replace('/[(0-9)]/', '', $field->Type);
			}
		}
		// If we want the whole field data object add that to the list.
		else
		{
			foreach ($fields as $field)
			{
				$field->Default = preg_replace("/(^(\(\(|\('|\(N'|\()|(('\)|(?<!\()\)\)|\))$))/i", '', $field->Default);
				$result[$field->Field] = $field;
			}
		}

		return $result;
	}

	/**
	 * Shows the table CREATE statement that creates the given tables.
	 *
	 * This is unsupported by MSSQL.
	 *
	 * @param   mixed  $tables  A table name or a list of table names.
	 *
	 * @return  array  A list of the create SQL for the tables.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function getTableCreate($tables)
	{
		$this->connect();

		return '';
	}

	/**
	 * Get the details list of keys for a table.
	 *
	 * @param   string  $table  The name of the table.
	 *
	 * @return  array  An array of the column specification for the table.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function getTableKeys($table)
	{
		$this->connect();

		// TODO To implement.
		return array();
	}

	/**
	 * Method to get an array of all tables in the database.
	 *
	 * @return  array  An array of all the tables in the database.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function getTableList()
	{
		$this->connect();

		// Set the query to get the tables statement.
		$this->setQuery('SELECT name FROM ' . $this->getDatabase() . '.sys.Tables WHERE type = \'U\';');
		$tables = $this->loadColumn();

		return $tables;
	}

	/**
	 * Get the version of the database connector.
	 *
	 * @return  string  The database connector version.
	 *
	 * @since   12.1
	 */
	public function getVersion()
	{
		$this->connect();

		$version = sqlsrv_server_info($this->connection);

		return $version['SQLServerVersion'];
	}

	/**
	 * Inserts a row into a table based on an object's properties.
	 *
	 * @param   string  $table    The name of the database table to insert into.
	 * @param   object  &$object  A reference to an object whose public properties match the table fields.
	 * @param   string  $key      The name of the primary key. If provided the object property is updated.
	 *
	 * @return  boolean    True on success.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function insertObject($table, &$object, $key = null)
	{
		$fields = array();
		$values = array();
		$statement = 'INSERT INTO ' . $this->quoteName($table) . ' (%s) VALUES (%s)';

		foreach (get_object_vars($object) as $k => $v)
		{
			// Only process non-null scalars.
			if (is_array($v) or is_object($v) or $v === null)
			{
				continue;
			}

			if (!$this->checkFieldExists($table, $k))
			{
				continue;
			}

			if ($k[0] == '_')
			{
				// Internal field
				continue;
			}

			if ($k == $key && $key == 0)
			{
				continue;
			}

			$fields[] = $this->quoteName($k);
			$values[] = $this->Quote($v);
		}
		// Set the query and execute the insert.
		$this->setQuery(sprintf($statement, implode(',', $fields), implode(',', $values)));

		if (!$this->execute())
		{
			return false;
		}

		$id = $this->insertid();

		if ($key && $id)
		{
			$object->$key = $id;
		}

		return true;
	}

	/**
	 * Method to get the auto-incremented value from the last INSERT statement.
	 *
	 * @return  integer  The value of the auto-increment field from the last inserted row.
	 *
	 * @since   12.1
	 */
	public function insertid()
	{
		$this->connect();

		// TODO: SELECT IDENTITY
		$this->setQuery('SELECT @@IDENTITY');

		return (int) $this->loadResult();
	}

	/**
	 * Execute the SQL statement.
	 *
	 * @return  mixed  A database cursor resource on success, boolean false on failure.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 * @throws  Exception
	 */
	public function execute()
	{
		$this->connect();

		// Take a local copy so that we don't modify the original query and cause issues later
		$query = $this->replacePrefix((string) $this->sql);

		if (!($this->sql instanceof JDatabaseQuery) && ($this->limit > 0 || $this->offset > 0))
		{
			$query = $this->limit($query, $this->limit, $this->offset);
		}

		if (!is_resource($this->connection))
		{
			JLog::add(JText::sprintf('JLIB_DATABASE_QUERY_FAILED', $this->errorNum, $this->errorMsg), JLog::ERROR, 'database');
			throw new JDatabaseExceptionExecuting($query, $this->errorMsg, $this->errorNum);
		}

		// Increment the query counter.
		$this->count++;

		// Reset the error values.
		$this->errorNum = 0;
		$this->errorMsg = '';

		// If debugging is enabled then let's log the query.
		if ($this->debug)
		{
			// Add the query to the object queue.
			$this->log[] = $query;

			JLog::add($query, JLog::DEBUG, 'databasequery');

			$this->timings[] = microtime(true);
		}

		// SQLSrv_num_rows requires a static or keyset cursor.
		if (strncmp(ltrim(strtoupper($query)), 'SELECT', strlen('SELECT')) == 0)
		{
			$array = array('Scrollable' => SQLSRV_CURSOR_KEYSET);
		}
		else
		{
			$array = array();
		}

		// Execute the query. Error suppression is used here to prevent warnings/notices that the connection has been lost.
		$this->cursor = @sqlsrv_query($this->connection, $query, array(), $array);

		if ($this->debug)
		{
			$this->timings[] = microtime(true);

			if (defined('DEBUG_BACKTRACE_IGNORE_ARGS'))
			{
				$this->callStacks[] = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
			}
			else
			{
				$this->callStacks[] = debug_backtrace();
			}
		}

		// If an error occurred handle it.
		if (!$this->cursor)
		{
			// Get the error number and message before we execute any more queries.
			$errorNum = $this->getErrorNumber();
			$errorMsg = $this->getErrorMessage();

			// Check if the server was disconnected.
			if (!$this->connected())
			{
				try
				{
					// Attempt to reconnect.
					$this->connection = null;
					$this->connect();
				}
				// If connect fails, ignore that exception and throw the normal exception.
				catch (RuntimeException $e)
				{
					// Get the error number and message.
					$this->errorNum = $this->getErrorNumber();
					$this->errorMsg = $this->getErrorMessage();

					// Throw the normal query exception.
					JLog::add(JText::sprintf('JLIB_DATABASE_QUERY_FAILED', $this->errorNum, $this->errorMsg), JLog::ERROR, 'database-error');

					throw new JDatabaseExceptionExecuting($query, $this->errorMsg, $this->errorNum, $e);
				}

				// Since we were able to reconnect, run the query again.
				return $this->execute();
			}
			// The server was not disconnected.
			else
			{
				// Get the error number and message from before we tried to reconnect.
				$this->errorNum = $errorNum;
				$this->errorMsg = $errorMsg;

				// Throw the normal query exception.
				JLog::add(JText::sprintf('JLIB_DATABASE_QUERY_FAILED', $this->errorNum, $this->errorMsg), JLog::ERROR, 'database-error');

				throw new JDatabaseExceptionExecuting($query, $this->errorMsg, $this->errorNum);
			}
		}

		return $this->cursor;
	}

	/**
	 * This function replaces a string identifier <var>$prefix</var> with the string held is the
	 * <var>tablePrefix</var> class variable.
	 *
	 * @param   string  $query   The SQL statement to prepare.
	 * @param   string  $prefix  The common table prefix.
	 *
	 * @return  string  The processed SQL statement.
	 *
	 * @since   12.1
	 */
	public function replacePrefix($query, $prefix = '#__')
	{
		$query = trim($query);

		if (strpos($query, "'"))
		{
			$parts = explode("'", $query);

			for ($nIndex = 0, $size = count($parts); $nIndex < $size; $nIndex = $nIndex + 2)
			{
				if (strpos($parts[$nIndex], $prefix) !== false)
				{
					$parts[$nIndex] = str_replace($prefix, $this->tablePrefix, $parts[$nIndex]);
				}
			}

			$query = implode("'", $parts);
		}
		else
		{
			$query = str_replace($prefix, $this->tablePrefix, $query);
		}

		return $query;
	}

	/**
	 * Select a database for use.
	 *
	 * @param   string  $database  The name of the database to select for use.
	 *
	 * @return  boolean  True if the database was successfully selected.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function select($database)
	{
		$this->connect();

		if (!$database)
		{
			return false;
		}

		if (!sqlsrv_query($this->connection, 'USE ' . $database, null, array('scrollable' => SQLSRV_CURSOR_STATIC)))
		{
			throw new JDatabaseExceptionConnecting('Could not connect to SQL Server database.');
		}

		return true;
	}

	/**
	 * Set the connection to use UTF-8 character encoding.
	 *
	 * @return  boolean  True on success.
	 *
	 * @since   12.1
	 */
	public function setUtf()
	{
		return false;
	}

	/**
	 * Method to commit a transaction.
	 *
	 * @param   boolean  $toSavepoint  If true, commit to the last savepoint.
	 *
	 * @return  void
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function transactionCommit($toSavepoint = false)
	{
		$this->connect();

		if (!$toSavepoint || $this->transactionDepth <= 1)
		{
			if ($this->setQuery('COMMIT TRANSACTION')->execute())
			{
				$this->transactionDepth = 0;
			}

			return;
		}

		$this->transactionDepth--;
	}

	/**
	 * Method to roll back a transaction.
	 *
	 * @param   boolean  $toSavepoint  If true, rollback to the last savepoint.
	 *
	 * @return  void
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function transactionRollback($toSavepoint = false)
	{
		$this->connect();

		if (!$toSavepoint || $this->transactionDepth <= 1)
		{
			if ($this->setQuery('ROLLBACK TRANSACTION')->execute())
			{
				$this->transactionDepth = 0;
			}

			return;
		}

		$savepoint = 'SP_' . ($this->transactionDepth - 1);
		$this->setQuery('ROLLBACK TRANSACTION ' . $this->quoteName($savepoint));

		if ($this->execute())
		{
			$this->transactionDepth--;
		}
	}

	/**
	 * Method to initialize a transaction.
	 *
	 * @param   boolean  $asSavepoint  If true and a transaction is already active, a savepoint will be created.
	 *
	 * @return  void
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function transactionStart($asSavepoint = false)
	{
		$this->connect();

		if (!$asSavepoint || !$this->transactionDepth)
		{
			if ($this->setQuery('BEGIN TRANSACTION')->execute())
			{
				$this->transactionDepth = 1;
			}

			return;
		}

		$savepoint = 'SP_' . $this->transactionDepth;
		$this->setQuery('BEGIN TRANSACTION ' . $this->quoteName($savepoint));

		if ($this->execute())
		{
			$this->transactionDepth++;
		}
	}

	/**
	 * Method to fetch a row from the result set cursor as an array.
	 *
	 * @param   mixed  $cursor  The optional result set cursor from which to fetch the row.
	 *
	 * @return  mixed  Either the next row from the result set or false if there are no more rows.
	 *
	 * @since   12.1
	 */
	protected function fetchArray($cursor = null)
	{
		return sqlsrv_fetch_array($cursor ? $cursor : $this->cursor, SQLSRV_FETCH_NUMERIC);
	}

	/**
	 * Method to fetch a row from the result set cursor as an associative array.
	 *
	 * @param   mixed  $cursor  The optional result set cursor from which to fetch the row.
	 *
	 * @return  mixed  Either the next row from the result set or false if there are no more rows.
	 *
	 * @since   12.1
	 */
	protected function fetchAssoc($cursor = null)
	{
		return sqlsrv_fetch_array($cursor ? $cursor : $this->cursor, SQLSRV_FETCH_ASSOC);
	}

	/**
	 * Method to fetch a row from the result set cursor as an object.
	 *
	 * @param   mixed   $cursor  The optional result set cursor from which to fetch the row.
	 * @param   string  $class   The class name to use for the returned row object.
	 *
	 * @return  mixed   Either the next row from the result set or false if there are no more rows.
	 *
	 * @since   12.1
	 */
	protected function fetchObject($cursor = null, $class = 'stdClass')
	{
		// Class has to be loaded for sqlsrv on windows platform
		class_exists($class);

		return sqlsrv_fetch_object($cursor ? $cursor : $this->cursor, $class);
	}

	/**
	 * Method to free up the memory used for the result set.
	 *
	 * @param   mixed  $cursor  The optional result set cursor from which to fetch the row.
	 *
	 * @return  void
	 *
	 * @since   12.1
	 */
	protected function freeResult($cursor = null)
	{
		sqlsrv_free_stmt($cursor ? $cursor : $this->cursor);
	}

	/**
	 * Method to check and see if a field exists in a table.
	 *
	 * @param   string  $table  The table in which to verify the field.
	 * @param   string  $field  The field to verify.
	 *
	 * @return  boolean  True if the field exists in the table.
	 *
	 * @since   12.1
	 */
	protected function checkFieldExists($table, $field)
	{
		$this->connect();

		$table = $this->replacePrefix((string) $table);
		$query = "SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = '$table' AND COLUMN_NAME = '$field' ORDER BY ORDINAL_POSITION";
		$this->setQuery($query);

		if ($this->loadResult())
		{
			return true;
		}
		else
		{
			return false;
		}
	}

	/**
	 * Method to wrap an SQL statement to provide a LIMIT and OFFSET behavior for scrolling through a result set.
	 *
	 * @param   string   $query   The SQL statement to process.
	 * @param   integer  $limit   The maximum affected rows to set.
	 * @param   integer  $offset  The affected row offset to set.
	 *
	 * @return  string   The processed SQL statement.
	 *
	 * @since   12.1
	 */
	protected function limit($query, $limit, $offset)
	{
		if ($limit)
		{
			$total = $offset + $limit;

			$position = stripos($query, 'SELECT');
			$distinct = stripos($query, 'SELECT DISTINCT');

			if ($position === $distinct)
			{
				$query = substr_replace($query, 'SELECT DISTINCT TOP ' . (int) $total, $position, 15);
			}
			else
			{
				$query = substr_replace($query, 'SELECT TOP ' . (int) $total, $position, 6);
			}
		}

		if (!$offset)
		{
			return $query;
		}

		return PHP_EOL
			. 'SELECT * FROM (SELECT *, ROW_NUMBER() OVER (ORDER BY (SELECT 0)) AS RowNumber FROM ('
			. $query
			. PHP_EOL . ') AS A) AS A WHERE RowNumber > ' . (int) $offset;
	}

	/**
	 * Renames a table in the database.
	 *
	 * @param   string  $oldTable  The name of the table to be renamed
	 * @param   string  $newTable  The new name for the table.
	 * @param   string  $backup    Table prefix
	 * @param   string  $prefix    For the table - used to rename constraints in non-mysql databases
	 *
	 * @return  JDatabaseDriverSqlsrv  Returns this object to support chaining.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function renameTable($oldTable, $newTable, $backup = null, $prefix = null)
	{
		$constraints = array();

		if (!is_null($prefix) && !is_null($backup))
		{
			$constraints = $this->getTableConstraints($oldTable);
		}

		if (!empty($constraints))
		{
			$this->renameConstraints($constraints, $prefix, $backup);
		}

		$this->setQuery("sp_rename '" . $oldTable . "', '" . $newTable . "'");

		return $this->execute();
	}

	/**
	 * Locks a table in the database.
	 *
	 * @param   string  $tableName  The name of the table to lock.
	 *
	 * @return  JDatabaseDriverSqlsrv  Returns this object to support chaining.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function lockTable($tableName)
	{
		return $this;
	}

	/**
	 * Unlocks tables in the database.
	 *
	 * @return  JDatabaseDriverSqlsrv  Returns this object to support chaining.
	 *
	 * @since   12.1
	 * @throws  RuntimeException
	 */
	public function unlockTables()
	{
		return $this;
	}

	/**
	 * Return the actual SQL Error number
	 *
	 * @return  integer  The SQL Error number
	 *
	 * @since   3.4.6
	 */
	protected function getErrorNumber()
	{
		$errors = sqlsrv_errors();

		return $errors[0]['code'];
	}

	/**
	 * Return the actual SQL Error message
	 *
	 * @return  string  The SQL Error message
	 *
	 * @since   3.4.6
	 */
	protected function getErrorMessage()
	{
		$errors       = sqlsrv_errors();
		$errorMessage = (string) $errors[0]['message'];

		// Replace the Databaseprefix with `#__` if we are not in Debug
		if (!$this->debug)
		{
			$errorMessage = str_replace($this->tablePrefix, '#__', $errorMessage);
		}

		return $errorMessage;
	}

	/**
	 * Get the query strings to alter the character set and collation of a table.
	 *
	 * @param   string  $tableName  The name of the table
	 *
	 * @return  string[]  The queries required to alter the table's character set and collation
	 *
	 * @since   CMS 3.5.0
	 */
	public function getAlterTableCharacterSet($tableName)
	{
		return array();
	}

	/**
	 * Return the query string to create new Database.
	 * Each database driver, other than MySQL, need to override this member to return correct string.
	 *
	 * @param   stdClass  $options  Object used to pass user and database name to database driver.
	 *                   This object must have "db_name" and "db_user" set.
	 * @param   boolean   $utf      True if the database supports the UTF-8 character set.
	 *
	 * @return  string  The query that creates database
	 *
	 * @since   12.2
	 */
	protected function getCreateDatabaseQuery($options, $utf)
	{
		return 'CREATE DATABASE ' . $this->quoteName($options->db_name);
	}
}
