<?php


/**
 * DbSimple_Generic: universal database connected by DSN.
 * (C) Dk Lab, http://en.dklab.ru
 *
 * This library 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.
 * See http://www.gnu.org/copyleft/lesser.html
 *
 * Use static DbSimple_Generic::connect($dsn) call if you don't know
 * database type and parameters, but have its DSN.
 * 
 * Additional keys can be added by appending a URI query string to the
 * end of the DSN.
 *
 * The format of the supplied DSN is in its fullest form:
 *   phptype(dbsyntax)://username:password@protocol+hostspec/database?option=8&another=true
 *
 * Most variations are allowed:
 *   phptype://username:password@protocol+hostspec:110//usr/db_file.db?mode=0644
 *   phptype://username:password@hostspec/database_name
 *   phptype://username:password@hostspec
 *   phptype://username@hostspec
 *   phptype://hostspec/database
 *   phptype://hostspec
 *   phptype(dbsyntax)
 *   phptype
 *
 * Parsing code is partially grabbed from PEAR DB class,
 * initial author: Tomas V.V.Cox <cox@idecnet.com>.
 * 
 * Contains 3 classes:
 * - DbSimple_Generic: database factory class
 * - DbSimple_Generic_Database: common database methods
 * - DbSimple_Generic_Blob: common BLOB support
 * - DbSimple_Generic_LastError: error reporting and tracking
 * 
 * Special result-set fields:
 * - ARRAY_KEY* ("*" means "anything")
 * - PARENT_KEY
 *
 * Transforms:
 * - GET_ATTRIBUTES
 * - CALC_TOTAL
 * - GET_TOTAL
 * - UNIQ_KEY
 * 
 * Query attributes:
 * - BLOB_OBJ
 * - CACHE
 *
 * @author Dmitry Koterov, http://forum.dklab.ru/users/DmitryKoterov/
 * @author Konstantin Zhinko, http://forum.dklab.ru/users/KonstantinGinkoTit/
 * 
 * @version 2.x $Id: Generic.php 226 2007-09-17 21:00:15Z dk $
 */

/**
 * Use this constant as placeholder value to skip optional SQL block [...].
 */
define('DBSIMPLE_SKIP', log(0));

/**
 * Names of special columns in result-set which is used
 * as array key (or karent key in forest-based resultsets) in 
 * resulting hash.
 */
define('DBSIMPLE_ARRAY_KEY', 'ARRAY_KEY');   // hash-based resultset support
define('DBSIMPLE_PARENT_KEY', 'PARENT_KEY'); // forrest-based resultset support


/**
 * DbSimple factory.
 */
class DbSimple_Generic
{
    /**
     * DbSimple_Generic connect(mixed $dsn)
     * 
     * Universal static function to connect ANY database using DSN syntax.
     * Choose database driver according to DSN. Return new instance
     * of this driver.
     */
    function& connect($dsn)
    {
        // Load database driver and create its instance.
        $parsed = DbSimple_Generic::parseDSN($dsn);
        if (!$parsed) {
            $dummy = null;
            return $dummy;
        }
        $class = 'DbSimple_'.ucfirst($parsed['scheme']);
        if (!class_exists($class)) {
            $file = str_replace('_', '/', $class) . ".php";
            // Try to load library file from standard include_path.
            if ($f = @fopen($file, "r", true)) {
                fclose($f);
                require_once($file);
            } else {
                // Wrong include_path; try to load from current directory.
                $base = basename($file);
                $dir = dirname(__FILE__);
                if (@is_file($path = "$dir/$base")) {
                    require_once($path);
                } else {
                    trigger_error("Error loading database driver: no file $file in include_path; no file $base in $dir", E_USER_ERROR);
                    return null;
                }
            }
        }
        $object =& new $class($parsed);
        if (isset($parsed['ident_prefix'])) {
            $object->setIdentPrefix($parsed['ident_prefix']);
        }
        $object->setCachePrefix(md5(serialize($parsed['dsn'])));
        if (@fopen('Cache/Lite.php', 'r', true)) {
            $tmp_dirs = array(
                ini_get('session.save_path'),
                getenv("TEMP"),
                getenv("TMP"),
                getenv("TMPDIR"),
                '/tmp'
            );
            foreach ($tmp_dirs as $dir) {
                if (!$dir) continue;
                $fp = @fopen($testFile = $dir . '/DbSimple_' . md5(getmypid() . microtime()), 'w');
                if ($fp) {
                    fclose($fp);
                    unlink($testFile);                
                    require_once 'Cache' . '/Lite.php'; // "." -> no phpEclipse notice
                    $t =& new Cache_Lite(array('cacheDir' => $dir.'/', 'lifeTime' => null, 'automaticSerialization' => true));
                    $object->_cacher =& $t;
                    break;
                }

            }
        }
        return $object;
    }
    

    /**
     * array parseDSN(mixed $dsn)
     * Parse a data source name.
     * See parse_url() for details. 
     */
    function parseDSN($dsn)
    {
        if (is_array($dsn)) return $dsn;
        $parsed = @parse_url($dsn);
        if (!$parsed) return null;
        $params = null;
        if (!empty($parsed['query'])) {
            parse_str($parsed['query'], $params);
            $parsed += $params;
        }
        $parsed['dsn'] = $dsn;
        return $parsed;
    }    
}

/**
 * Support for error tracking.
 * Can hold error messages, error queries and build proper stacktraces.
 */
class DbSimple_Generic_LastError
{
    var $error = null;
    var $errmsg = null;
    var $errorHandler = null;
    var $ignoresInTraceRe = 'DbSimple_.*::.* | call_user_func.*';

    /**
     * abstract void _logQuery($query)
     * Must be overriden in derived class.
     */
    function _logQuery($query)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);;
    }

    /**
     * void _resetLastError()
     * Reset the last error. Must be called on correct queries.
     */
    function _resetLastError()
    {
        $this->error = $this->errmsg = null;
    }

    /**
     * void _setLastError(int $code, string $message, string $query)
     * Fill $this->error property with error information. Error context
     * (code initiated the query outside DbSimple) is assigned automatically.
     */
    function _setLastError($code, $msg, $query)
    {
        $context = "unknown";
        if ($t = $this->findLibraryCaller()) {
            $context = (isset($t['file'])? $t['file'] : '?') . ' line ' . (isset($t['line'])? $t['line'] : '?');
        }
        $this->error = array(
            'code'    => $code,
            'message' => rtrim($msg),
            'query'   => $query,
            'context' => $context,
        );
        $this->errmsg = rtrim($msg) . ($context? " at $context" : "");

        $this->_logQuery("  -- error #".$code.": ".preg_replace('/(\r?\n)+/s', ' ', $this->errmsg));

        if (is_callable($this->errorHandler)) {
            call_user_func($this->errorHandler, $this->errmsg, $this->error);
        }

        return null;
    }


    /**
     * callback setErrorHandler(callback $handler)
     * Set new error handler called on database errors.
     * Handler gets 3 arguments:
     * - error message
     * - full error context information (last query etc.)
     */
    function setErrorHandler($handler)
    {
        $prev = $this->errorHandler;
        $this->errorHandler = $handler;
        // In case of setting first error handler for already existed
        // error - call the handler now (usual after connect()).
        if (!$prev && $this->error) {
            call_user_func($this->errorHandler, $this->errmsg, $this->error);
        }
        return $prev;
    }

    /**
     * void addIgnoreInTrace($reName)
     * Add regular expression matching ClassName::functionName or functionName.
     * Matched stack frames will be ignored in stack traces passed to query logger. 
     */    
    function addIgnoreInTrace($name)
    {
        $this->ignoresInTraceRe .= "|" . $name;
    }
    
    /**
     * array of array findLibraryCaller()
     * Return part of stacktrace before calling first library method.
     * Used in debug purposes (query logging etc.).
     */
    function findLibraryCaller()
    {
        $caller = call_user_func(
            array(&$this, 'debug_backtrace_smart'),
            $this->ignoresInTraceRe,
            true
        );
        return $caller;
    }
    
    /**
     * array debug_backtrace_smart($ignoresRe=null, $returnCaller=false)
     * 
     * Return stacktrace. Correctly work with call_user_func*
     * (totally skip them correcting caller references).
     * If $returnCaller is true, return only first matched caller,
     * not all stacktrace.
     * 
     * @version 2.03
     */
    function debug_backtrace_smart($ignoresRe=null, $returnCaller=false)
    {
        if (!is_callable($tracer='debug_backtrace')) return array();
        $trace = $tracer();
        
        if ($ignoresRe !== null) $ignoresRe = "/^(?>{$ignoresRe})$/six";
        $smart = array();
        $framesSeen = 0;
        for ($i=0, $n=count($trace); $i<$n; $i++) {
            $t = $trace[$i];
            if (!$t) continue;
                
            // Next frame.
            $next = isset($trace[$i+1])? $trace[$i+1] : null;
            
            // Dummy frame before call_user_func* frames.
            if (!isset($t['file'])) {
                $t['over_function'] = $trace[$i+1]['function'];
                $t = $t + $trace[$i+1];
                $trace[$i+1] = null; // skip call_user_func on next iteration
            }
            
            // Skip myself frame.
            if (++$framesSeen < 2) continue;

            // 'class' and 'function' field of next frame define where
            // this frame function situated. Skip frames for functions
            // situated in ignored places.
            if ($ignoresRe && $next) {
                // Name of function "inside which" frame was generated.
                $frameCaller = (isset($next['class'])? $next['class'].'::' : '') . (isset($next['function'])? $next['function'] : '');
                if (preg_match($ignoresRe, $frameCaller)) continue;
            }
            
            // On each iteration we consider ability to add PREVIOUS frame
            // to $smart stack.
            if ($returnCaller) return $t;
            $smart[] = $t;
        }
        return $smart;
    }
    
}

/**
 * Base class for all databases.
 * Can create transactions and new BLOBs, parse DSNs.
 * 
 * Logger is COMMON for multiple transactions.
 * Error handler is private for each transaction and database.
 */
class DbSimple_Generic_Database extends DbSimple_Generic_LastError
{
    /**
     * Public methods.
     */

    /**
     * object blob($blob_id)
     * Create new blob
     */
    function blob($blob_id = null)
    {
        $this->_resetLastError();
        return $this->_performNewBlob($blob_id);
    }
    
    /**
     * void transaction($mode)
     * Create new transaction.
     */
    function transaction($mode=null)
    {
        $this->_resetLastError();
        $this->_logQuery('-- START TRANSACTION '.$mode);
        return $this->_performTransaction($mode);
    }

    /**
     * mixed commit()
     * Commit the transaction.
     */
    function commit()
    {
        $this->_resetLastError();
        $this->_logQuery('-- COMMIT');
        return $this->_performCommit();
    }

    /**
     * mixed rollback()
     * Rollback the transaction.
     */
    function rollback()
    {
        $this->_resetLastError();
        $this->_logQuery('-- ROLLBACK');
        return $this->_performRollback();
    }

    /**
     * mixed select(string $query [, $arg1] [,$arg2] ...)
     * Execute query and return the result.
     */
    function select($query)
    {
        $args = func_get_args();
        $total = false;
        return $this->_query($args, $total);
    }
    
    /**
     * mixed selectPage(int &$total, string $query [, $arg1] [,$arg2] ...)
     * Execute query and return the result.
     * Total number of found rows (independent to LIMIT) is returned in $total
     * (in most cases second query is performed to calculate $total).
     */
    function selectPage(&$total, $query)
    {
        $args = func_get_args();
        array_shift($args);
        $total = true;
        return $this->_query($args, $total);
    }

    /**
     * hash selectRow(string $query [, $arg1] [,$arg2] ...)
     * Return the first row of query result.
     * On errors return null and set last error.
     * If no one row found, return array()! It is useful while debugging,
     * because PHP DOES NOT generates notice on $row['abc'] if $row === null
     * or $row === false (but, if $row is empty array, notice is generated).
     */
    function selectRow()
    {
        $args = func_get_args();
        $total = false;
        $rows = $this->_query($args, $total);
        if (!is_array($rows)) return $rows;
        if (!count($rows)) return array();
        reset($rows);
        return current($rows);
    }

    /**
     * array selectCol(string $query [, $arg1] [,$arg2] ...)
     * Return the first column of query result as array.
     */
    function selectCol()
    {
        $args = func_get_args();
        $total = false;
        $rows = $this->_query($args, $total);
        if (!is_array($rows)) return $rows;
        $this->_shrinkLastArrayDimensionCallback($rows);
        return $rows;
    }

    /**
     * scalar selectCell(string $query [, $arg1] [,$arg2] ...)
     * Return the first cell of the first column of query result.
     * If no one row selected, return null.
     */
    function selectCell()
    {
        $args = func_get_args();
        $total = false;
        $rows = $this->_query($args, $total);
        if (!is_array($rows)) return $rows;
        if (!count($rows)) return null;
        reset($rows);
        $row = current($rows);
        if (!is_array($row)) return $row;
        reset($row);
        return current($row);
    }

    /**
     * mixed query(string $query [, $arg1] [,$arg2] ...)
     * Alias for select(). May be used for INSERT or UPDATE queries.
     */
    function query()
    {
        $args = func_get_args();
        $total = false;
        return $this->_query($args, $total);
    }
    
    /**
     * string escape(mixed $s, bool $isIdent=false)
     * Enclose the string into database quotes correctly escaping
     * special characters. If $isIdent is true, value quoted as identifier 
     * (e.g.: `value` in MySQL, "value" in Firebird, [value] in MSSQL).
     */
    function escape($s, $isIdent=false)
    {
        return $this->_performEscape($s, $isIdent);
    }
    

    /**
     * callback setLogger(callback $logger)
     * Set query logger called before each query is executed.
     * Returns previous logger.
     */
    function setLogger($logger)
    {
        $prev = $this->_logger;
        $this->_logger = $logger;
        return $prev;
    }
    
    /**
     * callback setCacher(callback $cacher)
     * Set cache mechanism called during each query if specified.
     * Returns previous handler.
     */
    function setCacher($cacher)
    {
        $prev = $this->_cacher;
        $this->_cacher = $cacher;
        return $prev;
    }
    
    /**
     * string setIdentPrefix($prx)
     * Set identifier prefix used for $_ placeholder.
     */
    function setIdentPrefix($prx)
    {
        $old = $this->_identPrefix;
        if ($prx !== null) $this->_identPrefix = $prx;
        return $old;
    }

    /**
     * string setIdentPrefix($prx)
     * Set cache prefix used in key caclulation.
     */
    function setCachePrefix($prx)
    {
        $old = $this->_cachePrefix;
        if ($prx !== null) $this->_cachePrefix = $prx;
        return $old;
    }
    
    /**
     * array getStatistics()
     * Returns various statistical information.
     */
    function getStatistics()
    {
        return $this->_statistics;
    }


    /**
     * Virtual protected methods
     */
    function ____________PROTECTED() {} // for phpEclipse outline


    /**
     * string _performEscape(mixed $s, bool $isIdent=false)
     */
    function _performEscape($s, $isIdent)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }

    /**
     * object _performNewBlob($id)
     * 
     * Returns new blob object.
     */
    function& _performNewBlob($id)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }

    /**
     * list _performGetBlobFieldNames($resultResource)
     * Get list of all BLOB field names in result-set.
     */
    function _performGetBlobFieldNames($result)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }
    
    /**
     * mixed _performTransformQuery(array &$query, string $how)
     * 
     * Transform query different way specified by $how.
     * May return some information about performed transform.
     */
    function _performTransformQuery(&$queryMain, $how)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }
    
    
    /**
     * resource _performQuery($arrayQuery)
     * Must return:
     * - For SELECT queries: ID of result-set (PHP resource).
     * - For other  queries: query status (scalar).
     * - For error  queries: null (and call _setLastError()).
     */
    function _performQuery($arrayQuery)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }
    
    /**
     * mixed _performFetch($resultResource)
     * Fetch ONE NEXT row from result-set.
     * Must return:
     * - For SELECT queries: all the rows of the query (2d arrray).
     * - For INSERT queries: ID of inserted row.
     * - For UPDATE queries: number of updated rows.
     * - For other  queries: query status (scalar).
     * - For error  queries: null (and call _setLastError()).
     */
    function _performFetch($result)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }

    /**
     * array _performTotal($arrayQuery)
     */
    function _performTotal($arrayQuery)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }

    /**
     * mixed _performTransaction($mode)
     * Start new transaction.
     */
    function _performTransaction($mode=null)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }
    
    /**
     * mixed _performCommit()
     * Commit the transaction.
     */
    function _performCommit()
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }

    /**
     * mixed _performRollback()
     * Rollback the transaction.
     */
    function _performRollback()
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }
    
    /**
     * string _performGetPlaceholderIgnoreRe()
     * Return regular expression which matches ignored query parts.
     * This is needed to skip placeholder replacement inside comments, constants etc.
     */
    function _performGetPlaceholderIgnoreRe()
    {
        return '';
    }    
    
    /**
     * Returns marker for native database placeholder. E.g. in FireBird it is '?',
     * in PostgreSQL - '$1', '$2' etc.
     * 
     * @param int $n Number of native placeholder from the beginning of the query (begins from 0!).
     * @return string String representation of native placeholder marker (by default - '?').
     */
    function _performGetNativePlaceholderMarker($n)
    {
        return '?';
    }  
      
    
    /**
     * Private methods.
     */
    function ____________PRIVATE() {} // for phpEclipse outline     


    /**
     * array _query($query, &$total)
     * See _performQuery().
     */
    function _query($query, &$total)
    {
        $this->_resetLastError();
        
        // Fetch query attributes.
        $this->attributes = $this->_transformQuery($query, 'GET_ATTRIBUTES');

        // Modify query if needed for total counting.
        if ($total) {
            $this->_transformQuery($query, 'CALC_TOTAL');
        }
        $is_cacher_callable = (is_callable($this->_cacher) || (method_exists($this->_cacher, 'get') && method_exists($this->_cacher, 'save')));
        $rows = null;
        $cache_it = false;
        if (!empty($this->attributes['CACHE']) && $is_cacher_callable) {

            $hash = $this->_cachePrefix . md5(serialize($query));
            // Getting data from cache if possible
            $fetchTime = $firstFetchTime = 0;
            $qStart    = $this->_microtime();
            $cacheData = $this->_cache($hash);
            $queryTime = $this->_microtime() - $qStart;

            $storeTime  = isset($cacheData['storeTime'])  ? $cacheData['storeTime']  : null;
            $invalCache = isset($cacheData['invalCache']) ? $cacheData['invalCache'] : null;
            $result     = isset($cacheData['result'])     ? $cacheData['result']     : null; 
            $rows       = isset($cacheData['rows'])       ? $cacheData['rows']       : null; 


            $cache_params = $this->attributes['CACHE'];

            // Calculating cache time to live
            $re = '/
                (
                    ([0-9]+)           #2 - hours
                h)? [ \t]* 
                (
                    ([0-9]+)           #4 - minutes
                m)? [ \t]* 
                (
                    ([0-9]+)           #6 - seconds
                s?)? (,)?
            /sx';
            $m = null;
            preg_match($re, $cache_params, $m);
            $ttl = @$m[6] + @$m[4] * 60 + @$m[2] * 3600;
            // Cutting out time param - now there are just fields for uniqKey or nothing 
            $cache_params = trim(preg_replace($re, '', $cache_params, 1));

            $uniq_key = null;

            // UNIQ_KEY calculation
            if (!empty($cache_params)) {
                $dummy = null;
                // There is no need in query, cos' needle in $this->attributes['CACHE']
                $this->_transformQuery($dummy, 'UNIQ_KEY');
                $uniq_key = call_user_func_array(array(&$this, 'select'), $dummy);
                $uniq_key = md5(serialize($uniq_key));
            }
            // Check TTL?
            $ttl = empty($ttl) ? true : (int)$storeTime > (time() - $ttl);

            // Invalidate cache?
            if ($ttl && $uniq_key == $invalCache) {
                $this->_logQuery($query);
                $this->_logQueryStat($queryTime, $fetchTime, $firstFetchTime, $rows);

            }
            else $cache_it = true;
        } 

        if (null === $rows || true === $cache_it) {
            $this->_logQuery($query);

            // Run the query (counting time).
            $qStart = $this->_microtime();        
            $result = $this->_performQuery($query);
            $fetchTime = $firstFetchTime = 0;

            if (is_resource($result)) {
                $rows = array();
                // Fetch result row by row.
                $fStart = $this->_microtime();
                $row = $this->_performFetch($result);
                $firstFetchTime = $this->_microtime() - $fStart;
                if ($row !== null) {
                    $rows[] = $row;
                    while ($row=$this->_performFetch($result)) {
                        $rows[] = $row;
                    }
                }
                $fetchTime = $this->_microtime() - $fStart;
            } else {
                $rows = $result;
            }
            $queryTime = $this->_microtime() - $qStart;

            // Log query statistics.
            $this->_logQueryStat($queryTime, $fetchTime, $firstFetchTime, $rows);
            
            // Prepare BLOB objects if needed.
            if (is_array($rows) && !empty($this->attributes['BLOB_OBJ'])) {
                $blobFieldNames = $this->_performGetBlobFieldNames($result);
                foreach ($blobFieldNames as $name) {
                    for ($r = count($rows)-1; $r>=0; $r--) {
                        $rows[$r][$name] =& $this->_performNewBlob($rows[$r][$name]);
                    }
                }
            }
    
            // Transform resulting rows.
            $result = $this->_transformResult($rows);

            // Storing data in cache
            if ($cache_it && $is_cacher_callable) {
                $this->_cache(
                    $hash,
                    array(
                        'storeTime'  => time(),
                        'invalCache' => $uniq_key,
                        'result'     => $result,
                        'rows'       => $rows
                    )
                );
            }

        }
        // Count total number of rows if needed.
        if (is_array($result) && $total) {
            $this->_transformQuery($query, 'GET_TOTAL');
            $total = call_user_func_array(array(&$this, 'selectCell'), $query);
        }

        return $result;
    }
    
    
    /**
     * mixed _transformQuery(array &$query, string $how)
     * 
     * Transform query different way specified by $how.
     * May return some information about performed transform.
     */
    function _transformQuery(&$query, $how)
    {
        // Do overriden transformation.
        $result = $this->_performTransformQuery($query, $how);
        if ($result === true) return $result;
        // Common transformations.
        switch ($how) {
            case 'GET_ATTRIBUTES':
                // Extract query attributes.
                $options = array();
                $q = $query[0];
                $m = null;
                while (preg_match('/^ \s* -- [ \t]+ (\w+): ([^\r\n]+) [\r\n]* /sx', $q, $m)) {
                    $options[$m[1]] = trim($m[2]);
                    $q = substr($q, strlen($m[0]));
                }
                return $options;
            case 'UNIQ_KEY':
                $q = $this->attributes['CACHE'];
                $i = 0;
                $query = "  -- UNIQ_KEY\n";
                while(preg_match('/(\w+)\.\w+/sx', $q, $m)) {
                    if($i > 0)$query .= "\nUNION\n";
                    $query .= 'SELECT MAX('.$m[0].') AS M, COUNT(*) AS C FROM '.$m[1];
                    $q = substr($q, strlen($m[0]));
                    $i++;
                }
                return true;
        }
        // No such transform.
        $this->_setLastError(-1, "No such transform type: $how", $query);
    }
        
        
    /**
     * void _expandPlaceholders(array &$queryAndArgs, bool $useNative=false)
     * Replace placeholders by quoted values.
     * Modify $queryAndArgs.
     */
    function _expandPlaceholders(&$queryAndArgs, $useNative=false)
    {
        $cacheCode = null;
        if ($this->_logger) {
            // Serialize is much faster than placeholder expansion. So use caching.
            $cacheCode = md5(serialize($queryAndArgs) . '|' . $useNative . '|' . $this->_identPrefix);
            if (isset($this->_placeholderCache[$cacheCode])) {
                $queryAndArgs = $this->_placeholderCache[$cacheCode];
                return;
            }
        }
        
        if (!is_array($queryAndArgs)) {
            $queryAndArgs = array($queryAndArgs);
        }

        $this->_placeholderNativeArgs = $useNative? array() : null;
        $this->_placeholderArgs = array_reverse($queryAndArgs);

        $query = array_pop($this->_placeholderArgs); // array_pop is faster than array_shift

        // Do all the work.
        $this->_placeholderNoValueFound = false;
        $query = $this->_expandPlaceholdersFlow($query);

        if ($useNative) {
            array_unshift($this->_placeholderNativeArgs, $query);
            $queryAndArgs = $this->_placeholderNativeArgs;
        } else {
            $queryAndArgs = array($query);
        }
        
        if ($cacheCode) {
            $this->_placeholderCache[$cacheCode] = $queryAndArgs;
        }
    }

        
    /**
     * Do real placeholder processing.
     * Imply that all interval variables (_placeholder_*) already prepared.
     * May be called recurrent!
     */
    function _expandPlaceholdersFlow($query)
    {
        $re = '{
            (?>
                # Ignored chunks.
                (?>
                    # Comment. 
                    -- [^\r\n]* 
                ) 
                  |
                (?> 
                    # DB-specifics.
                    ' . trim($this->_performGetPlaceholderIgnoreRe()) . '
                )
            ) 
              |
            (?> 
                # Optional blocks
                \{
                    # Use "+" here, not "*"! Else nested blocks are not processed well.
                    ( (?> (?>[^{}]+)  |  (?R) )* )             #1
                \}
            )
              |
            (?>
                # Placeholder
                (\?) ( [_dsafn\#]? )                           #2 #3
            )
        }sx';
        $query = preg_replace_callback(
            $re,
            array(&$this, '_expandPlaceholdersCallback'), 
            $query
        );
        return $query;
    }
    

    /**
     * string _expandPlaceholdersCallback(list $m)
     * Internal function to replace placeholders (see preg_replace_callback).
     */
    function _expandPlaceholdersCallback($m)
    {
        // Placeholder.
        if (!empty($m[2])) {
            $type = $m[3];
            
            // Idenifier prefix.
            if ($type == '_') {
                return $this->_identPrefix;
            }
            
            // Value-based placeholder.
            if (!$this->_placeholderArgs) return 'DBSIMPLE_ERROR_NO_VALUE';
            $value = array_pop($this->_placeholderArgs);

            // Skip this value?
            if ($value === DBSIMPLE_SKIP) {
                $this->_placeholderNoValueFound = true;
                return '';
            }
            
            // First process guaranteed non-native placeholders.
            switch ($type) {
                case 'a':
                    if (!$value) $this->_placeholderNoValueFound = true;
                    if (!is_array($value)) return 'DBSIMPLE_ERROR_VALUE_NOT_ARRAY';
                    $parts = array();
                    foreach ($value as $k=>$v) {
                        $v = $v === null? 'NULL' : $this->escape($v);
                        if (!is_int($k)) {
                            $k = $this->escape($k, true);
                            $parts[] = "$k=$v";
                        } else {
                            $parts[] = $v;
                        }
                    }
                    return join(', ', $parts);
                case "#":
                    // Identifier.
                    if (!is_array($value)) return $this->escape($value, true);
                    $parts = array();
                    foreach ($value as $table => $identifier) {
                        if (!is_string($identifier)) return 'DBSIMPLE_ERROR_ARRAY_VALUE_NOT_STRING';
                        $parts[] = (!is_int($table)? $this->escape($table, true) . '.' : '') . $this->escape($identifier, true);
                    }
                    return join(', ', $parts);
                case 'n':
                    // NULL-based placeholder.
                    return empty($value)? 'NULL' : intval($value);
            }

            // Native arguments are not processed.
            if ($this->_placeholderNativeArgs !== null) {
                $this->_placeholderNativeArgs[] = $value;
                return $this->_performGetNativePlaceholderMarker(count($this->_placeholderNativeArgs) - 1);
            } 
            
            // In non-native mode arguments are quoted.
            if ($value === null) return 'NULL';
            switch ($type) {
                case '':
                    if (!is_scalar($value)) return 'DBSIMPLE_ERROR_VALUE_NOT_SCALAR';
                    return $this->escape($value);
                case 'd': 
                    return intval($value);
                case 'f':
                    return str_replace(',', '.', floatval($value));
            }
            // By default - escape as string.
            return $this->escape($value);
        }
        
        // Optional block.
        if (isset($m[1]) && strlen($block=$m[1])) {
            $prev = @$this->_placeholderNoValueFound;
            $block = $this->_expandPlaceholdersFlow($block);
            $block = $this->_placeholderNoValueFound? '' : ' ' . $block . ' ';
            $this->_placeholderNoValueFound = $prev; // recurrent-safe            
            return $block;
        }
        
        // Default: skipped part of the string.
        return $m[0];
    }
    
    
    /**
     * void _setLastError($code, $msg, $query)
     * Set last database error context.
     * Aditionally expand placeholders.
     */
    function _setLastError($code, $msg, $query)
    {
        if (is_array($query)) {
            $this->_expandPlaceholders($query, false);
            $query = $query[0];
        }
        return DbSimple_Generic_LastError::_setLastError($code, $msg, $query);
    }
    
    
    /**
     * Return microtime as float value.
     */
    function _microtime()
    {
        $t = explode(" ", microtime());
        return $t[0] + $t[1];
    }
    
    
    /**
     * Convert SQL field-list to COUNT(...) clause
     * (e.g. 'DISTINCT a AS aa, b AS bb' -> 'COUNT(DISTINCT a, b)').
     */
    function _fieldList2Count($fields)
    {
        $m = null;
        if (preg_match('/^\s* DISTINCT \s* (.*)/sx', $fields, $m)) {
            $fields = $m[1];
            $fields = preg_replace('/\s+ AS \s+ .*? (?=,|$)/sx', '', $fields);
            return "COUNT(DISTINCT $fields)";
        } else {
            return 'COUNT(*)';
        }
    }


    /**
     * array _transformResult(list $rows)
     * Transform resulting rows to various formats.
     */
    function _transformResult($rows)
    {
        // Process ARRAY_KEY feature.
        if (is_array($rows) && $rows) {
            // Find ARRAY_KEY* AND PARENT_KEY fields in field list.
            $pk = null;
            $ak = array();
            foreach (current($rows) as $fieldName => $dummy) {
                if (0 == strncasecmp($fieldName, DBSIMPLE_ARRAY_KEY, strlen(DBSIMPLE_ARRAY_KEY))) {
                    $ak[] = $fieldName;
                } else if (0 == strncasecmp($fieldName, DBSIMPLE_PARENT_KEY, strlen(DBSIMPLE_PARENT_KEY))) {
                    $pk = $fieldName;
                }
            }
            natsort($ak); // sort ARRAY_KEY* using natural comparision
            
            if ($ak) {
                // Tree-based array? Fields: ARRAY_KEY, PARENT_KEY
                if ($pk !== null) {
                    return $this->_transformResultToForest($rows, $ak[0], $pk);
                }
                // Key-based array? Fields: ARRAY_KEY.
                return $this->_transformResultToHash($rows, $ak);
            }
        }
        return $rows;
    }


    /**
     * Converts rowset to key-based array.
     * 
     * @param array $rows   Two-dimensional array of resulting rows.
     * @param array $ak     List of ARRAY_KEY* field names.
     * @return array        Transformed array.
     */
    function _transformResultToHash($rows, $arrayKeys)
    {
        $arrayKeys = (array)$arrayKeys;
        $result = array();
        foreach ($rows as $row) {
            // Iterate over all of ARRAY_KEY* fields and build array dimensions.
            $current =& $result;
            foreach ($arrayKeys as $ak) {
                $key = $row[$ak];
                unset($row[$ak]); // remove ARRAY_KEY* field from result row
                if ($key !== null) {
                    $current =& $current[$key];
                } else {
                    // IF ARRAY_KEY field === null, use array auto-indices.
                    $tmp = array();
                    $current[] =& $tmp;
                    $current =& $tmp;
                    unset($tmp); // we use tmp because don't know the value of auto-index
                }
            }
            $current = $row; // save the row in last dimension
        }
        return $result;
    }


    /**
     * Converts rowset to the forest.
     * 
     * @param array $rows       Two-dimensional array of resulting rows.
     * @param string $idName    Name of ID field.
     * @param string $pidName   Name of PARENT_ID field.
     * @return array            Transformed array (tree).
     */
    function _transformResultToForest($rows, $idName, $pidName)
    {
        $children = array(); // children of each ID
        $ids = array();
        // Collect who are children of whom.
        foreach ($rows as $i=>$r) {
            $row =& $rows[$i];
            $id = $row[$idName];
            if ($id === null) {
                // Rows without an ID are totally invalid and makes the result tree to 
                // be empty (because PARENT_ID = null means "a root of the tree"). So 
                // skip them totally.
                continue;
            }
            $pid = $row[$pidName];
            if ($id == $pid) $pid = null;
            $children[$pid][$id] =& $row;
            if (!isset($children[$id])) $children[$id] = array();
            $row['childNodes'] =& $children[$id];
            $ids[$id] = true;
        }
        // Root elements are elements with non-found PIDs.
        $forest = array();
        foreach ($rows as $i=>$r) {
            $row =& $rows[$i];
            $id = $row[$idName];
            $pid = $row[$pidName];
            if ($pid == $id) $pid = null;
            if (!isset($ids[$pid])) {
                $forest[$row[$idName]] =& $row;
            }
            unset($row[$idName]); 
            unset($row[$pidName]);
        }
        return $forest;
    }


    /**
     * Replaces the last array in a multi-dimensional array $V by its first value.
     * Used for selectCol(), when we need to transform (N+1)d resulting array
     * to Nd array (column).
     */
    function _shrinkLastArrayDimensionCallback(&$v)
    {
        if (!$v) return;
        reset($v);
        if (!is_array($firstCell = current($v))) {
            $v = $firstCell;
        } else {
            array_walk($v, array(&$this, '_shrinkLastArrayDimensionCallback'));
        }
    }

    /**
     * void _logQuery($query, $noTrace=false)
     * Must be called on each query.
     * If $noTrace is true, library caller is not solved (speed improvement).
     */
    function _logQuery($query, $noTrace=false)
    {
        if (!$this->_logger) return;
        $this->_expandPlaceholders($query, false);
        $args = array();
        $args[] =& $this;
        $args[] = $query[0];
        $args[] = $noTrace? null : $this->findLibraryCaller();
        return call_user_func_array($this->_logger, $args);
    }
    
    
    /**
     * void _logQueryStat($queryTime, $fetchTime, $firstFetchTime, $rows)
     * Log information about performed query statistics.
     */
    function _logQueryStat($queryTime, $fetchTime, $firstFetchTime, $rows)
    {
        // Always increment counters.
        $this->_statistics['time'] += $queryTime;
        $this->_statistics['count']++;
        
        // If no logger, economize CPU resources and actually log nothing.
        if (!$this->_logger) return;
        
        $dt = round($queryTime * 1000);
        $firstFetchTime = round($firstFetchTime*1000);
        $tailFetchTime = round($fetchTime * 1000) - $firstFetchTime;
        $log = "  -- ";
        if ($firstFetchTime + $tailFetchTime) {
            $log = sprintf("  -- %d ms = %d+%d".($tailFetchTime? "+%d" : ""), $dt, $dt-$firstFetchTime-$tailFetchTime, $firstFetchTime, $tailFetchTime);
        } else {
            $log = sprintf("  -- %d ms", $dt);
        }
        $log .= "; returned ";

        if (!is_array($rows)) {
            $log .= $this->escape($rows); 
        } else {
            $detailed = null;
            if (count($rows) == 1) {
                $len = 0;
                $values = array();
                foreach ($rows[0] as $k=>$v) {
                    $len += strlen($v);
                    if ($len > $this->MAX_LOG_ROW_LEN) {
                        break;
                    }
                    $values[] = $v === null? 'NULL' : $this->escape($v);
                }
                if ($len <= $this->MAX_LOG_ROW_LEN) {
                    $detailed = "(" . preg_replace("/\r?\n/", "\\n", join(', ', $values)) . ")";
                }
            }
            if ($detailed) {
                $log .= $detailed;
            } else {
                $log .= count($rows). " row(s)";
            }
        }
        
        $this->_logQuery($log, true);
    }
    
    /**
     * mixed _cache($hash, $result=null)
     * Calls cache mechanism if possible.
     */
    function _cache($hash, $result=null)
    {
        if (is_callable($this->_cacher)) {
            return call_user_func($this->_cacher, $hash, $result);
        } else if (is_object($this->_cacher) && method_exists($this->_cacher, 'get') && method_exists($this->_cacher, 'save')) {
            if (null === $result)
                return $this->_cacher->get($hash);
            else
                $this->_cacher->save($result, $hash);
        }
        else return false;
    }
    
    
    /**
     * protected constructor(string $dsn)
     * 
     * Prevent from direct creation of this object.
     */
    function DbSimple_Generic_Database()
    {
        die("This is protected constructor! Do not instantiate directly at ".__FILE__." line ".__LINE__);
    }
    
    // Identifiers prefix (used for ?_ placeholder).
    var $_identPrefix = '';

    // Queries statistics.
    var $_statistics = array(
        'time'  => 0,
        'count' => 0,
    );
    
    var $_cachePrefix = '';

    var $_logger = null;
    var $_cacher = null;
    var $_placeholderArgs, $_placeholderNativeArgs, $_placeholderCache=array();
    var $_placeholderNoValueFound;
    
    /**
     * When string representation of row (in characters) is greater than this,
     * row data will not be logged.
    */
    var $MAX_LOG_ROW_LEN = 128;
}

/**
 * Database BLOB.
 * Can read blob chunk by chunk, write data to BLOB.
 */
class DbSimple_Generic_Blob extends DbSimple_Generic_LastError
{
    /**
     * string read(int $length)
     * Returns following $length bytes from the blob.
     */
    function read($len)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }

    /**
     * string write($data)
     * Appends data to blob.
     */
    function write($data)
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }

    /**
     * int length()
     * Returns length of the blob.
     */
    function length()
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }

    /**
     * blobid close()
     * Closes the blob. Return its ID. No other way to obtain this ID!
     */
    function close()
    {
        die("Method must be defined in derived class. Abstract function called at ".__FILE__." line ".__LINE__);
    }
}