class SQL
{
    private $_connection;

    public function __construct( $arguments = null )
    {
        /**
         *  Assign default credentials - you can also load and assign these from another file, to keep the SQL class clean and
         *  do something like Config::getSQLCredentials();
         */
        $this->hostname = 'host';
        $this->username = 'user';
        $this->password = 'password';
        $this->database = 'database';

        // Overwrite default credentials, if any arguments has been passed
        if( $arguments !== null && is_array( $arguments ) && count( $arguments ) )
        {
            if( array_key_exists( 'hostname', $arguments ) )
                $this->hostname = $arguments[ 'hostname' ];

            if( array_key_exists( 'database', $arguments ) )
                $this->database = $arguments[ 'database' ];

            if( array_key_exists( 'username', $arguments ) )
                $this->username = $arguments[ 'username' ];

            if( array_key_exists( 'password', $arguments ) )
                $this->password = $arguments[ 'password' ];
        }

        $this->_connection = new \mysqli
        (
            $this->hostname,
            $this->username,
            $this->password,
            $this->database
        );
    }

    public function __destruct()
    {
        mysqli_close( $this->_connection );
    }

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

    private function getConnection()
    {
        if ( !$this->_connection )
            die( 'Connection not initialized, aborting..' );

        return $this->_connection;
    }
}

// ---- MAIN ----

$sql = new SQL();

// OR

$sql = new SQL(
                  array
                  (
                      'hostname' => 'asd',
                      'password' => 'asr2we99sdf'
                  )
              );