PHP Datetime format with Codeigniter default timezone

/**
     * This function can convert 3 date formats:
     *  - 2019-11-20T15:34:03.000+0300      
     *  - 2019-11-19T17:21:53Z
     *  - unix time with 000 at the end
     * @param type $timestamp
     * @return date("Y-m-d H:i:s") with app default timezone
     */
    function dateTimeFormat($timestamp = NULL)
    {
        if ((empty($timestamp)) || (is_null($timestamp)) || (is_object($timestamp)) || (is_array($timestamp)))
        {
            return $timestamp;
        }
        elseif (is_numeric($timestamp) && (strlen($timestamp) == 13) && (substr($timestamp, -3) == "000"))
        {
            $timestamp = substr($timestamp, 0, -3);
            return $this->getTime($timestamp, date_default_timezone_get());
        }
        elseif (preg_match('/^' .
                        '(\d{4})-(\d{2})-(\d{2})T' . // YYYY-MM-DDT ex: 2014-01-01T
                        '(\d{2}):(\d{2}):(\d{2})' . // HH-MM-SS  ex: 17:00:00
                        '(Z|((-|\+)\d{2}:\d{2}))' . // Z or +01:00 or -01:00
                        '$/', $timestamp, $parts) == true)
        {
            return $this->getTime(strtotime($timestamp), date_default_timezone_get());
        }
        elseif (preg_match('/^' .
                        '(\d{4})-(\d{2})-(\d{2})T' . // YYYY-MM-DDT ex: 2014-01-01T
                        '(\d{2}):(\d{2}):(\d{2})' . // HH-MM-SS  ex: 17:00:00
                        '(.\d{3})' .
                        '(((-|\+)\d{4}))' . // Z or +01:00 or -01:00
                        '$/', $timestamp, $parts) == true)
        {
            $timestamp = str_replace("T", ' ', substr($timestamp, 0, 19));
            return $this->getTime(strtotime($timestamp), date_default_timezone_get());
        }
        return $timestamp;
    }

    /**
     * Return date for specific timezone
     * @param type $timestamp   input: 1518404518,America/Los_Angeles 
     * @param type $timezone
     * @return type
     */
    function getTime($timestamp, $timezone)
    {
        try
        {
            $date = new DateTime(date("Y-m-d H:i:s", $timestamp));
            $date->setTimezone(new DateTimeZone($timezone));
            $rt   = $date->format('Y-m-d H:i:s'); /* output: Feb 11, 2018 7:01:58 pm */
            return $rt;
        }
        catch (\Exception $e)
        {
            log_message('error', "Library->Helpers::ts2time: Error on time conversion: $timestamp | $e");
            return "";
        }
    }