PHPOffice / PhpSpreadsheet

        // Execute function

        $excelDateValue = \PhpOffice\PhpSpreadsheet\Shared\Date::formattedPHPToExcel($year, $month, $day);

        switch (Functions::getReturnDateType()) {

            case Functions::RETURNDATE_EXCEL:

                return (float) $excelDateValue;

            case Functions::RETURNDATE_PHP_NUMERIC:

                return (integer) \PhpOffice\PhpSpreadsheet\Shared\Date::excelToTimestamp($excelDateValue);

            case Functions::RETURNDATE_PHP_OBJECT:

                return \PhpOffice\PhpSpreadsheet\Shared\Date::excelToDateTimeObject($excelDateValue);

        }

    }

    /**

            }

        }

        switch (Functions::getReturnDateType()) {

            case Functions::RETURNDATE_EXCEL:

                return (float) $endDate;

            case Functions::RETURNDATE_PHP_NUMERIC:

                return (integer) \PhpOffice\PhpSpreadsheet\Shared\Date::excelToTimestamp($endDate);

            case Functions::RETURNDATE_PHP_OBJECT:

                return \PhpOffice\PhpSpreadsheet\Shared\Date::excelToDateTimeObject($endDate);

        }

    }

    /**

        // Execute function

        $PHPDateObject = self::adjustDateByMonths($dateValue, $adjustmentMonths);

        switch (Functions::getReturnDateType()) {

            case Functions::RETURNDATE_EXCEL:

                return (float) \PhpOffice\PhpSpreadsheet\Shared\Date::PHPToExcel($PHPDateObject);

            case Functions::RETURNDATE_PHP_NUMERIC:

                return (integer) \PhpOffice\PhpSpreadsheet\Shared\Date::excelToTimestamp(\PhpOffice\PhpSpreadsheet\Shared\Date::PHPToExcel($PHPDateObject));

            case Functions::RETURNDATE_PHP_OBJECT:

                return $PHPDateObject;

        }

    }

    /**

        $adjustDaysString = '-' . $adjustDays . ' days';

        $PHPDateObject->modify($adjustDaysString);

        switch (Functions::getReturnDateType()) {

            case Functions::RETURNDATE_EXCEL:

                return (float) \PhpOffice\PhpSpreadsheet\Shared\Date::PHPToExcel($PHPDateObject);

            case Functions::RETURNDATE_PHP_NUMERIC:

                return (integer) \PhpOffice\PhpSpreadsheet\Shared\Date::excelToTimestamp(\PhpOffice\PhpSpreadsheet\Shared\Date::PHPToExcel($PHPDateObject));

            case Functions::RETURNDATE_PHP_OBJECT:

                return $PHPDateObject;

        }

    }

}