class SQL extends PDO {

    private static $instance = null;
    private $dsn;
    private $userName;
    private $password;
    private $options;
    private $serverName;
    private $returnType;
    private $tablePrefix;
    private $charSet;
    private static $command;
    private $data;
    private $fetchMode;

    private function __clone() {

    }


    public static function getInstance($serverName = 'db', $fetchMode = PDO::FETCH_OBJ) {
        if (!isset(self::$instance)) {
            self::$instance = new SQL($serverName, $fetchMode);
        }
        return self::$instance;
    }

    private function loadConfig() {
        $configPath = 'server->' . $this->serverName . '_' . RUN_MODE . '->';
        $this->dsn = Config::read($configPath . 'dsn');
        $this->userName = Config::read($configPath . 'userName');
        $this->password = Config::read($configPath . 'password');
        $this->tablePrefix = Config::read($configPath . 'tablePrefix');
        $this->charSet = Config::read($configPath . 'charSet');
        $this->options = array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES '" . $this->charSet . "'");
    }

    public function __construct($serverName, $fetchMode) {
        $this->serverName = $serverName;
        $this->fetchMode = $fetchMode;

        $this->loadConfig();
        parent::__construct($this->dsn, $this->userName, $this->password, $this->options);
        parent::setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }

    private function parseCommand() {
        foreach ($this->data as $value) {
            if (!is_numeric($value)) {
                $this->data[] = parent::quote($value);
            }
        }
        $commandVars = '';
        $commandValues = '';
        if (preg_match_all(' /\{(.*?)}/', self::$command, $variables)) {

            $commandVars = $variables[0];
            for ($i = 0; $i < count($variables[1]); $i++) {
                $commandValues [] = $this->tablePrefix . $variables[1][$i];
            }
        }
        self::$command = vsprintf(str_replace($commandVars, $commandValues, self::$command), $this->data);
        $return = explode(' ', self::$command);
        $this->returnType = $return[0];
    }

    public function execute() {

        $this->data = func_get_args();
        self::$command = $this->data[0];
        array_shift($this->data);
        $this->parseCommand();

        if (strtolower($this->returnType) == 'select') {
            $command = $this->prepare(self::$command);
            $command->setFetchMode($this->fetchMode);
            $command->execute();
            self::$command = '';
            return $command->fetchAll();
        } else {
            $command = false;
            try {
                $command = $this->exec(self::$command);
            } catch (PDOException $err) {
                // echo $err->getMessage();
            }

            self::$command = '';
            if ($command == false) {
                return false;
            } else {
                return true;
            }
        }
    }

}