timezone-functions.php

<?php

/*
* Set timezone used internally by PHP. See full list at https://www.php.net/manual/en/timezones.php
*
* @access   public
* @param    string  $tz     Timezone, e.g., America/Mexico_City
* @return
* @author   Quinn Comendant <quinn@strangecode.com>
* @since    28 Jan 2019 16:38:38
*/
public function setTimezone($tz)
{
    // Set timezone for PHP.
    if (date_default_timezone_set($tz)) {
        $this->logMsg(sprintf('Using php timezone: %s', $tz), LOG_DEBUG, __FILE__, __LINE__);
    } else {
        // Failed!
        $this->logMsg(sprintf('Failed to set php timezone: %s', $tz), LOG_WARNING, __FILE__, __LINE__);
    }
}

/*
* Create a DateTime object from a string and convert its timezone.
*
* @access   public
* @param    string  $datetime   A date-time string or unit timestamp, e.g., `now + 60 days` or `1606165903`.
* @param    string  $from_tz    A PHP timezone, e.g., UTC
* @param    string  $to_tz      A PHP timezone, e.g., America/Mexico_City
* @return   DateTime            A DateTime object ready to use with, e.g., ->format(…).
* @author   Quinn Comendant <quinn@strangecode.com>
* @since    23 Nov 2020 15:08:45
*/
function convertTZ($datetime, $from_tz, $to_tz)
{
    if (preg_match('/^\d+$/', $datetime)) {
        // It's a timestamp, format as required by DateTime::__construct().
        $datetime = "@$datetime";
    }

    $dt = new DateTime($datetime, new DateTimeZone($from_tz));
    $dt->setTimezone(new DateTimeZone($to_tz));

    return $dt;
}

/*
* Convert a given date-time string from php_timezone to user_timezone, and return formatted.
*
* @access   public
* @param    string  $datetime   A date-time string or unit timestamp, e.g., `now + 60 days` or `1606165903`.
* @param    string  $format     A date format string for DateTime->format(…) or strftime(…). Set to lc_date_format by default.
* @return   string              A formatted date in the user's timezone.
* @author   Quinn Comendant <quinn@strangecode.com>
* @since    23 Nov 2020 15:13:26
*/
function dateToUserTZ($datetime, $format=null)
{
    if (empty($datetime) || in_array($datetime, ['0000-00-00 00:00:00', '0000-00-00', '1000-01-01 00:00:00', '1000-01-01'])) {
        // Zero dates in MySQL should never be displayed.
        return '';
    }

    try {
        // Create a DateTime object and convert the timezone from server to user.
        $dt = $this->convertTZ($datetime, $this->getParam('php_timezone'), $this->getParam('user_timezone'));
    } catch (Exception $e) {
        $this->logMsg(sprintf('DateTime failed to parse string in %s: %s', __METHOD__, $datetime), LOG_NOTICE, __FILE__, __LINE__);
        return '';
    }

    // By default, we try to use a localized date format. Set lc_date_format to null to use regular date_format instead.
    $format = $format ?: $this->getParam('lc_date_format');
    if ($format && mb_strpos($format, '%') !== false) {
        // The data format is localized for strftime(). It only accepts a timestamp, which are always in UTC, so we hack this by offering the date from the user's timezone in a format without a TZ specified, which is used to a make a timestamp for strftime (we can't use DaateTime->format('U') because that would convert the date back to UTC).
        return strftime($format, strtotime($dt->format('Y-m-d H:i:s')));
    } else {
        // Otherwise use a regular date format.
        $format = $format ?: $this->getParam('date_format');
        return $dt->format($format);
    }
}

/*
* Convert a given date-time string from user_timezone to php_timezone, and formatted as YYYY-MM-DD HH:MM:SS.
*
* @access   public
* @param    string  $datetime   A date-time string or unit timestamp, e.g., `now + 60 days` or `1606165903`.
* @param    string  $format     A date format string for DateTime->format(…). Set to 'Y-m-d H:i:s' by default.
* @return   string              A formatted date in the server's timezone.
* @author   Quinn Comendant <quinn@strangecode.com>
* @since    23 Nov 2020 15:13:26
*/
function dateToServerTZ($datetime, $format='Y-m-d H:i:s')
{
    try {
        // Create a DateTime object and conver the timezone from server to user.
        $dt = $this->convertTZ($datetime, $this->getParam('user_timezone'), $this->getParam('php_timezone'));
    } catch (Exception $e) {
        $this->logMsg(sprintf('DateTime failed to parse string in %s: %s', __METHOD__, $datetime), LOG_NOTICE, __FILE__, __LINE__);
        return '';
    }

    return $dt->format($format);
}