<?php
/**
 * ownCloud
 *
 * @author Frank Karlitschek
 * @copyright 2012 Frank Karlitschek frank@owncloud.org
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE
 * License as published by the Free Software Foundation; either
 * version 3 of the License, or any later version.
 *
 * This library 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 AFFERO GENERAL PUBLIC LICENSE for more details.
 *
 * You should have received a copy of the GNU Affero General Public
 * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

define('MDB2_SCHEMA_DUMP_STRUCTURE', '1');

class DatabaseException extends Exception {
	private $query;

	public function __construct($message, $query) {
		parent::__construct($message);
		$this->query = $query;
	}

	public function getQuery() {
		return $this->query;
	}
}

/**
 * This class manages the access to the database. It basically is a wrapper for
 * Doctrine with some adaptions.
 */
class OC_DB {
	const BACKEND_DOCTRINE=2;

	static private $preparedQueries = array();
	static private $cachingEnabled = true;

	/**
	 * @var \Doctrine\DBAL\Connection
	 */
	static private $connection; //the prefered connection to use, only Doctrine
	static private $backend=null;
	/**
	 * @var Doctrine
	 */
	static private $DOCTRINE=null;

	static private $inTransaction=false;
	static private $prefix=null;
	static private $type=null;

	/**
	 * check which backend we should use
	 * @return int BACKEND_DOCTRINE
	 */
	private static function getDBBackend() {
		return self::BACKEND_DOCTRINE;
	}

	/**
	 * @brief connects to the database
	 * @param int $backend
	 * @return bool true if connection can be established or false on error
	 *
	 * Connects to the database as specified in config.php
	 */
	public static function connect($backend=null) {
		if(self::$connection) {
			return true;
		}
		if(is_null($backend)) {
			$backend=self::getDBBackend();
		}
		if($backend==self::BACKEND_DOCTRINE) {
			$success = self::connectDoctrine();
			self::$connection=self::$DOCTRINE;
			self::$backend=self::BACKEND_DOCTRINE;
		}
		return $success;
	}

	/**
	 * connect to the database using doctrine
	 *
	 * @return bool
	 */
	public static function connectDoctrine() {
		if(self::$connection) {
			if(self::$backend!=self::BACKEND_DOCTRINE) {
				self::disconnect();
			} else {
				return true;
			}
		}
		self::$preparedQueries = array();
		// The global data we need
		$name = OC_Config::getValue( "dbname", "owncloud" );
		$host = OC_Config::getValue( "dbhost", "" );
		$user = OC_Config::getValue( "dbuser", "" );
		$pass = OC_Config::getValue( "dbpassword", "" );
		$type = OC_Config::getValue( "dbtype", "sqlite" );
		if(strpos($host, ':')) {
			list($host, $port)=explode(':', $host, 2);
		} else {
			$port=false;
		}

		// do nothing if the connection already has been established
		if(!self::$DOCTRINE) {
			$config = new \Doctrine\DBAL\Configuration();
			switch($type) {
				case 'sqlite':
				case 'sqlite3':
					$datadir=OC_Config::getValue( "datadirectory", OC::$SERVERROOT.'/data' );
					$connectionParams = array(
							'user' => $user,
							'password' => $pass,
							'path' => $datadir.'/'.$name.'.db',
							'driver' => 'pdo_sqlite',
					);
					break;
				case 'mysql':
					$connectionParams = array(
							'user' => $user,
							'password' => $pass,
							'host' => $host,
							'port' => $port,
							'dbname' => $name,
							'charset' => 'UTF8',
							'driver' => 'pdo_mysql',
					);
					break;
				case 'pgsql':
					$connectionParams = array(
							'user' => $user,
							'password' => $pass,
							'host' => $host,
							'port' => $port,
							'dbname' => $name,
							'driver' => 'pdo_mysql',
					);
					break;
				case 'oci':
					$connectionParams = array(
							'user' => $user,
							'password' => $pass,
							'host' => $host,
							'port' => $port,
							'dbname' => $name,
							'charset' => 'AL32UTF8',
							'driver' => 'oci8',
					);
					break;
				case 'mssql':
					$dsn = array(
						'phptype' => 'sqlsrv',
						'username' => $user,
						'password' => $pass,
						'hostspec' => $host,
						'database' => $name
					);                    
					break;
				default:
					return false;
			}
			try {
				self::$DOCTRINE = \Doctrine\DBAL\DriverManager::getConnection($connectionParams, $config);
			} catch(\Doctrine\DBAL\DBALException $e) {
				OC_Log::write('core', $e->getMessage(), OC_Log::FATAL);
				OC_User::setUserId(null);

				// send http status 503
				header('HTTP/1.1 503 Service Temporarily Unavailable');
				header('Status: 503 Service Temporarily Unavailable');
				OC_Template::printErrorPage('Failed to connect to database');
				die();
			}
		}
		return true;
	}

	/**
	 * @brief Prepare a SQL query
	 * @param string $query Query string
	 * @param int $limit
	 * @param int $offset
	 * @return \Doctrine\DBAL\Statement prepared SQL query
	 *
	 * SQL query via Doctrine prepare(), needs to be execute()'d!
	 */
	static public function prepare( $query , $limit=null, $offset=null ) {

		if (!is_null($limit) && $limit != -1) {
			//Doctrine does not handle limit and offset.
			//FIXME: check limit notation for other dbs
			//the following sql thus might needs to take into account db ways of representing it
			//(oracle has no LIMIT / OFFSET)
			$limit = (int)$limit;
			$limitsql = ' LIMIT ' . $limit;
			if (!is_null($offset)) {
				$offset = (int)$offset;
				$limitsql .= ' OFFSET ' . $offset;
			}
			//insert limitsql
			if (substr($query, -1) == ';') { //if query ends with ;
				$query = substr($query, 0, -1) . $limitsql . ';';
			} else {
				$query.=$limitsql;
			}
		} else {
			if (isset(self::$preparedQueries[$query]) and self::$cachingEnabled) {
				return self::$preparedQueries[$query];
			}
		}
		$rawQuery = $query;

		// Optimize the query
		$query = self::processQuery( $query );

		self::connect();
		// return the result
		if (self::$backend == self::BACKEND_DOCTRINE) {
			try {
				$result=self::$connection->prepare($query);
			} catch(\Doctrine\DBAL\DBALException $e) {
				throw new DatabaseException($e->getMessage(), $query);
			}
			$result=new DoctrineStatementWrapper($result);
		}
		if ((is_null($limit) || $limit == -1) and self::$cachingEnabled ) {
			$type = OC_Config::getValue( "dbtype", "sqlite" );
			if( $type != 'sqlite' && $type != 'sqlite3' ) {
				self::$preparedQueries[$rawQuery] = $result;
			}
		}
		return $result;
	}

	/**
	 * @brief gets last value of autoincrement
	 * @param string $table The optional table name (will replace *PREFIX*) and add sequence suffix
	 * @return int id
	 *
	 * \Doctrine\DBAL\Connection lastInsertId
	 *
	 * Call this method right after the insert command or other functions may
	 * cause trouble!
	 */
	public static function insertid($table=null) {
		self::connect();
		$type = OC_Config::getValue( "dbtype", "sqlite" );
		if( $type == 'pgsql' ) {
			$query = self::prepare('SELECT lastval() AS id');
			$row = $query->execute()->fetchRow();
			return $row['id'];
		}
		if( $type == 'mssql' ) {
			if($table !== null) {
				$prefix = OC_Config::getValue( "dbtableprefix", "oc_" );
				$table = str_replace( '*PREFIX*', $prefix, $table );
			}
			return self::$connection->lastInsertId($table);
		} else {
			if($table !== null) {
				$prefix = OC_Config::getValue( "dbtableprefix", "oc_" );
				$suffix = OC_Config::getValue( "dbsequencesuffix", "_id_seq" );
				$table = str_replace( '*PREFIX*', $prefix, $table ).$suffix;
			}
			return self::$connection->lastInsertId($table);
		}
	}

	/**
	 * @brief Disconnect
	 * @return bool
	 *
	 * This is good bye, good bye, yeah!
	 */
	public static function disconnect() {
		// Cut connection if required
		if(self::$connection) {
			self::$connection=false;
			self::$DOCTRINE=false;
		}

		return true;
	}

	/** else {
	 * @brief saves database scheme to xml file
	 * @param string $file name of file
	 * @param int $mode
	 * @return bool
	 *
	 * TODO: write more documentation
	 */
	public static function getDbStructure( $file, $mode=MDB2_SCHEMA_DUMP_STRUCTURE) {
		self::connectDoctrine();
		return OC_DB_Schema::getDbStructure(self::$connection, $file);
	}

	/**
	 * @brief Creates tables from XML file
	 * @param string $file file to read structure from
	 * @return bool
	 *
	 * TODO: write more documentation
	 */
	public static function createDbFromStructure( $file ) {
		self::connectDoctrine();
		return OC_DB_Schema::createDbFromStructure(self::$connection, $file);
		/* FIXME: use CURRENT_TIMESTAMP for all databases. mysql supports it as a default for DATETIME since 5.6.5 [1]
		 * as a fallback we could use <default>0000-01-01 00:00:00</default> everywhere
		 * [1] http://bugs.mysql.com/bug.php?id=27645
		 * http://dev.mysql.com/doc/refman/5.0/en/timestamp-initialization.html
		 * http://www.postgresql.org/docs/8.1/static/functions-datetime.html
		 * http://www.sqlite.org/lang_createtable.html
		 * http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions037.htm
		 */
		if( $CONFIG_DBTYPE == 'pgsql' ) { //mysql support it too but sqlite doesn't
			$content = str_replace( '<default>0000-00-00 00:00:00</default>',
				'<default>CURRENT_TIMESTAMP</default>', $content );
		}
	}

	/**
	 * @brief update the database scheme
	 * @param string $file file to read structure from
	 * @return bool
	 */
	public static function updateDbFromStructure($file) {
		self::connectDoctrine();
		try {
			$result = OC_DB_Schema::updateDbFromStructure(self::$connection, $file);
		} catch (Exception $e) {
			OC_Log::write('core', 'Failed to update database structure ('.$e.')', OC_Log::FATAL);
			throw $e;
		}
		return $result;
		/* FIXME: use CURRENT_TIMESTAMP for all databases. mysql supports it as a default for DATETIME since 5.6.5 [1]
		 * as a fallback we could use <default>0000-01-01 00:00:00</default> everywhere
		 * [1] http://bugs.mysql.com/bug.php?id=27645
		 * http://dev.mysql.com/doc/refman/5.0/en/timestamp-initialization.html
		 * http://www.postgresql.org/docs/8.1/static/functions-datetime.html
		 * http://www.sqlite.org/lang_createtable.html
		 * http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions037.htm
		 */
		if( $CONFIG_DBTYPE == 'pgsql' ) { //mysql support it too but sqlite doesn't
			$content = str_replace( '<default>0000-00-00 00:00:00</default>',
				'<default>CURRENT_TIMESTAMP</default>', $content );
		}
	}

	/**
	 * @brief Insert a row if a matching row doesn't exists.
	 * @param string $table. The table to insert into in the form '*PREFIX*tableName'
	 * @param array $input. An array of fieldname/value pairs
	 * @returns The return value from DoctrineStatementWrapper->execute()
	 */
	public static function insertIfNotExist($table, $input) {
		self::connect();
		$prefix = OC_Config::getValue( "dbtableprefix", "oc_" );
		$table = str_replace( '*PREFIX*', $prefix, $table );

		if(is_null(self::$type)) {
			self::$type=OC_Config::getValue( "dbtype", "sqlite" );
		}
		$type = self::$type;

		$query = '';
		// differences in escaping of table names ('`' for mysql) and getting the current timestamp
		if( $type == 'sqlite' || $type == 'sqlite3' ) {
			// NOTE: For SQLite we have to use this clumsy approach
			// otherwise all fieldnames used must have a unique key.
			$query = 'SELECT * FROM "' . $table . '" WHERE ';
			foreach($input as $key => $value) {
				$query .= $key . " = '" . $value . '\' AND ';
			}
			$query = substr($query, 0, strlen($query) - 5);
			try {
				$stmt = self::prepare($query);
				$result = $stmt->execute();
			} catch(\Doctrine\DBAL\DBALException $e) {
				$entry = 'DB Error: "'.$e->getMessage() . '"<br />';
				$entry .= 'Offending command was: ' . $query . '<br />';
				OC_Log::write('core', $entry, OC_Log::FATAL);
				error_log('DB error: '.$entry);
				OC_Template::printErrorPage( $entry );
			}

			if($result->numRows() == 0) {
				$query = 'INSERT INTO "' . $table . '" ("'
					. implode('","', array_keys($input)) . '") VALUES("'
					. implode('","', array_values($input)) . '")';
			} else {
				return true;
			}
		} elseif( $type == 'pgsql' || $type == 'oci' || $type == 'mysql' || $type == 'mssql') {
			$query = 'INSERT INTO `' .$table . '` ('
				. implode(',', array_keys($input)) . ') SELECT \''
				. implode('\',\'', array_values($input)) . '\' FROM ' . $table . ' WHERE ';

			foreach($input as $key => $value) {
				$query .= $key . " = '" . $value . '\' AND ';
			}
			$query = substr($query, 0, strlen($query) - 5);
			$query .= ' HAVING COUNT(*) = 0';
		}

		// TODO: oci should be use " (quote) instead of ` (backtick).
		//OC_Log::write('core', __METHOD__ . ', type: ' . $type . ', query: ' . $query, OC_Log::DEBUG);

		try {
			$result = self::prepare($query);
		} catch(\Doctrine\DBAL\DBALException $e) {
			$entry = 'DB Error: "'.$e->getMessage() . '"<br />';
			$entry .= 'Offending command was: ' . $query.'<br />';
			OC_Log::write('core', $entry, OC_Log::FATAL);
			error_log('DB error: ' . $entry);
			OC_Template::printErrorPage( $entry );
		}

		return $result->execute();
	}

	/**
	 * @brief does minor changes to query
	 * @param string $query Query string
	 * @return string corrected query string
	 *
	 * This function replaces *PREFIX* with the value of $CONFIG_DBTABLEPREFIX
	 * and replaces the ` with ' or " according to the database driver.
	 */
	private static function processQuery( $query ) {
		self::connect();
		// We need Database type and table prefix
		if(is_null(self::$type)) {
			self::$type=OC_Config::getValue( "dbtype", "sqlite" );
		}
		$type = self::$type;
		if(is_null(self::$prefix)) {
			self::$prefix=OC_Config::getValue( "dbtableprefix", "oc_" );
		}
		$prefix = self::$prefix;

		// differences in escaping of table names ('`' for mysql) and getting the current timestamp
		if( $type == 'sqlite' || $type == 'sqlite3' ) {
			$query = str_replace( '`', '"', $query );
			$query = str_ireplace( 'NOW()', 'datetime(\'now\')', $query );
			$query = str_ireplace( 'UNIX_TIMESTAMP()', 'strftime(\'%s\',\'now\')', $query );
		} elseif( $type == 'pgsql' ) {
			$query = str_replace( '`', '"', $query );
			$query = str_ireplace( 'UNIX_TIMESTAMP()', 'cast(extract(epoch from current_timestamp) as integer)',
				$query );
		} elseif( $type == 'oci'  ) {
			$query = str_replace( '`', '"', $query );
			$query = str_ireplace( 'NOW()', 'CURRENT_TIMESTAMP', $query );
		}elseif( $type == 'mssql' ) {
			$query = preg_replace( "/\`(.*?)`/", "[$1]", $query );
			$query = str_replace( 'NOW()', 'CURRENT_TIMESTAMP', $query );
			$query = str_replace( 'now()', 'CURRENT_TIMESTAMP', $query );
			$query = str_replace( 'LENGTH(', 'LEN(', $query );
			$query = str_replace( 'SUBSTR(', 'SUBSTRING(', $query );
            
            $query = self::fixLimitClauseForMSSQL($query);
        }

		// replace table name prefix
		$query = str_replace( '*PREFIX*', $prefix, $query );

		return $query;
	}

    private static function fixLimitClauseForMSSQL($query) {
        $limitLocation = stripos ($query, "LIMIT");
        
        if ( $limitLocation === false ) {
            return $query;
        } 
        
        // total == 0 means all results - not zero results
        //
        // First number is either total or offset, locate it by first space
        //
        $offset = substr ($query, $limitLocation + 5);
        $offset = substr ($offset, 0, stripos ($offset, ' '));
        $offset = trim ($offset);

        // check for another parameter
        if (stripos ($offset, ',') === false) {
            // no more parameters
            $offset = 0;
            $total = intval ($offset);
        } else {
            // found another parameter
            $offset = intval ($offset);

            $total = substr ($query, $limitLocation + 5);
            $total = substr ($total, stripos ($total, ','));

            $total = substr ($total, 0, stripos ($total, ' '));
            $total = intval ($total);
        }

        $query = trim (substr ($query, 0, $limitLocation));

        if ($offset == 0 && $total !== 0) {
            if (strpos($query, "SELECT") === false) {
                $query = "TOP {$total} " . $query;
            } else {
                $query = preg_replace('/SELECT(\s*DISTINCT)?/Dsi', 'SELECT$1 TOP '.$total, $query);
            }
        } else if ($offset > 0) {
            $query = preg_replace('/SELECT(\s*DISTINCT)?/Dsi', 'SELECT$1 TOP(10000000) ', $query);
            $query = 'SELECT *
                    FROM (SELECT sub2.*, ROW_NUMBER() OVER(ORDER BY sub2.line2) AS line3
                    FROM (SELECT 1 AS line2, sub1.* FROM (' . $query . ') AS sub1) as sub2) AS sub3';

            if ($total > 0) {
                $query .= ' WHERE line3 BETWEEN ' . ($offset + 1) . ' AND ' . ($offset + $total);
            } else {
                $query .= ' WHERE line3 > ' . $offset;
            }
        }
        return $query;
    }
    
	/**
	 * @brief drop a table
	 * @param string $tableName the table to drop
	 */
	public static function dropTable($tableName) {
		self::connectDoctrine();
		OC_DB_Schema::dropTable(self::$connection, $tableName);
	}

	/**
	 * remove all tables defined in a database structure xml file
	 * @param string $file the xml file describing the tables
	 */
	public static function removeDBStructure($file) {
		self::connectDoctrine();
		OC_DB_Schema::removeDBStructure(self::$connection, $file);
	}

	/**
	 * @brief replaces the owncloud tables with a new set
	 * @param $file string path to the MDB2 xml db export file
	 */
	public static function replaceDB( $file ) {
		self::connectDoctrine();
		OC_DB_Schema::replaceDB(self::$connection, $file);
	}

	/**
	 * Start a transaction
	 * @return bool
	 */
	public static function beginTransaction() {
		self::connect();
		self::$connection->beginTransaction();
		self::$inTransaction=true;
		return true;
	}

	/**
	 * Commit the database changes done during a transaction that is in progress
	 * @return bool
	 */
	public static function commit() {
		self::connect();
		if(!self::$inTransaction) {
			return false;
		}
		self::$connection->commit();
		self::$inTransaction=false;
		return true;
	}

	/**
	 * check if a result is an error, works with Doctrine
	 * @param mixed $result
	 * @return bool
	 */
	public static function isError($result) {
		if(!$result) {
			return true;
		} else {
			return false;
		}
	}

	/**
	 * returns the error code and message as a string for logging
	 * works with DoctrineException
	 * @param mixed $error
	 * @return string
	 */
	public static function getErrorMessage($error) {
		if (self::$backend==self::BACKEND_DOCTRINE and self::$DOCTRINE) {
			$msg = self::$DOCTRINE->errorCode() . ': ';
			$errorInfo = self::$DOCTRINE->errorInfo();
			if (is_array($errorInfo)) {
				$msg .= 'SQLSTATE = '.$errorInfo[0] . ', ';
				$msg .= 'Driver Code = '.$errorInfo[1] . ', ';
				$msg .= 'Driver Message = '.$errorInfo[2];
			} else {
				$msg = '';
			}
		} else {
			$msg = '';
		}
		return $msg;
	}

	/**
	 * @param bool $enabled
	 */
	static public function enableCaching($enabled) {
		if (!$enabled) {
			self::$preparedQueries = array();
		}
		self::$cachingEnabled = $enabled;
	}
}

/**
 * small wrapper around \Doctrine\DBAL\Driver\Statement to make it behave, more like an MDB2 Statement
 */
class DoctrineStatementWrapper {
	/**
	 * @var \Doctrine\DBAL\Driver\Statement
	 */
	private $statement=null;
	private $lastArguments=array();

	public function __construct($statement) {
		$this->statement=$statement;
	}

	/**
	 * pass all other function directly to the \Doctrine\DBAL\Driver\Statement
	 */
	public function __call($name,$arguments) {
		return call_user_func_array(array($this->statement,$name), $arguments);
	}

	/**
	 * provide numRows
	 */
	public function numRows() {
		return $this->statement->rowCount();
	}

	/**
	 * make execute return the result instead of a bool
	 */
	public function execute($input=array()) {
		$this->lastArguments = $input;
		if (count($input) > 0) {

			if (!isset($type)) {
				$type = OC_Config::getValue( "dbtype", "sqlite" );
			}

			if ($type == 'mssql') {
				$input = $this->tryFixSubstringLastArgumentDataForMSSQL($input);
			}

			$result=$this->statement->execute($input);
		} else {
			$result=$this->statement->execute();
		}
		
		if ($result) {
			return $this;
		} else {
			return false;
		}
	}

	private function tryFixSubstringLastArgumentDataForMSSQL($input) {
		$query = $this->statement->queryString;
		$pos = stripos ($query, 'SUBSTRING');

		if ( $pos === false) {
			return;
		}

		try {
			$newQuery = '';

			$cArg = 0;

			$inSubstring = false;

			// Create new query
			for ($i = 0; $i < strlen ($query); $i++) {
				if ($inSubstring == false) {
					// Defines when we should start inserting values
					if (substr ($query, $i, 9) == 'SUBSTRING') {
						$inSubstring = true;
					}
				} else {
					// Defines when we should stop inserting values
					if (substr ($query, $i, 1) == ')') {
						$inSubstring = false;
					}
				}

				if (substr ($query, $i, 1) == '?') {
					// We found a question mark
					if ($inSubstring) {
						$newQuery .= $input[$cArg];

						//
						// Remove from input array
						//
						array_splice ($input, $cArg, 1);
					} else {
						$newQuery .= substr ($query, $i, 1);
						$cArg++;
					}
				} else {
					$newQuery .= substr ($query, $i, 1);
				}
			}

			// The global data we need
			$name = OC_Config::getValue( "dbname", "owncloud" );
			$host = OC_Config::getValue( "dbhost", "" );
			$user = OC_Config::getValue( "dbuser", "" );
			$pass = OC_Config::getValue( "dbpassword", "" );
			if (strpos($host,':')) {
				list($host, $port) = explode(':', $host, 2);
			} else {
				$port = false;
			}
			$opts = array();

			if ($port) {
				$dsn = 'sqlsrv:Server='.$host.','.$port.';Database='.$name;
			} else {
				$dsn = 'sqlsrv:Server='.$host.';Database='.$name;
			}

			$PDO = new PDO($dsn, $user, $pass, $opts);
			$PDO->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
			$PDO->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

			$this->statement = $PDO->prepare($newQuery);

			$this->lastArguments = $input;

			return $input;
		} catch (PDOException $e){
			$entry = 'PDO DB Error: "'.$e->getMessage().'"<br />';
			$entry .= 'Offending command was: '.$this->statement->queryString .'<br />';
			$entry .= 'Input parameters: ' .print_r($input, true).'<br />';
			$entry .= 'Stack trace: ' .$e->getTraceAsString().'<br />';
			OC_Log::write('core', $entry, OC_Log::FATAL);
			OC_User::setUserId(null);

			// send http status 503
			header('HTTP/1.1 503 Service Temporarily Unavailable');
			header('Status: 503 Service Temporarily Unavailable');
			OC_Template::printErrorPage('Failed to connect to database');
			die ($entry);
		}
	}
    
	/**
	 * provide an alias for fetch
	 */
	public function fetchRow() {
		return $this->statement->fetch();
	}

	/**
	 * Provide a simple fetchOne.
	 * fetch single column from the next row
	 * @param int $colnum the column number to fetch
	 */
	public function fetchOne($colnum = 0) {
		return $this->statement->fetchColumn($colnum);
	}
}