test time zone conversion using carbon

carbon-test-tz-conversion.php

<?php
        // date/time variables using CarbonImmutable: https://carbon.nesbot.com/docs/
        //set user time zone
        $userTimeZone = 'Europe/London';
        
        //======================= UTC ==============================================
        //now in UTC
        //CarbonImmutable i.e. don't change the hour value when switching timezones
        $nowUTC = CarbonImmutable::now('UTC');
        //$nowUTC = CarbonImmutable::parse('2020-05-31 23:12:58 UTC');
        //$nowUTC = CarbonImmutable::parse('2020-05-30 23:00:00 UTC');
        //$nowUTC = CarbonImmutable::parse('2020-05-31 01:00:00 UTC');
        //var_dump($nowUTC->isoFormat('YYYY-MM-DD HH:mm:ss ZZ'));
        //hour now in UTC
        $hourNowUTCFormatted = $nowUTC->isoFormat('HH'); // Carbon: HH == hour 00..23
        //minute now in UTC
        $minuteNowUTCFormatted = $nowUTC->isoFormat('mm'); // Carbon: mm == minute 00..59
        //minute now in UTC
        $secondNowUTCFormatted = $nowUTC->isoFormat('ss'); // Carbon: mm == minute 00..59
        //date now in UTC
        $dateNowUTCFormatted = $nowUTC->isoFormat('YYYY-MM-DD');
        //date yesterday in UTC
        $dateYesterdayUTCFormatted = $nowUTC->yesterday()->isoFormat('YYYY-MM-DD');

        //======================= userTimeZone ====================================
        //now timezone Europe/London
        $nowUserTimeZone = $nowUTC->setTimezone($userTimeZone);
        //var_dump($nowUserTimeZone->tzName);
        //var_dump($nowUserTimeZone->isoFormat('YYYY-MM-DD HH:mm:ss ZZ'));
        //echo "\n\n";
        $nowUserTimeZoneDateMonthDayFormatted = $nowUserTimeZone->isoFormat('MMM DD');
        $nowUserTimeZoneDateMonthDayYearFormatted = $nowUserTimeZone->isoFormat('MMM DD, YYYY');
        //hour now, timezone Europe/London
        $hourNowUserTimeZoneFormatted = $nowUserTimeZone->isoFormat('HH');
        //+1 hour from now, timezone Europe/London
        $hourNextUserTimeZoneFormatted = $nowUserTimeZone->add('1 hour')->isoFormat('HH');

        //======================= userTimeZone convert to UTC =======================
        //Convert from time zone to UTC
        //get time an hour ago
        $oneHourAgoUserTimeZone = $nowUserTimeZone->sub('1 hour');
        //Get current time in userTimeZone start of day: YYYY-MM-DD 00:00:00
        $startOfDayUserTimeZone = $oneHourAgoUserTimeZone->startOfDay();
        //Convert start of day, from userTimeZone to UTC: i.e. today Europe/London at 00:00:00 -> yesterday UTC 23:00:00
        $startOfDayUserTimeZoneToUTC = $startOfDayUserTimeZone->setTimezone('UTC')->isoFormat('YYYY-MM-DD HH:mm:ss');
        //fix for start of day, 00:00:00-00:59:59 europe/london time
        if ($nowUserTimeZone->isoFormat('HH') == "00") {
            $oneHourAgoEndOfHourUserTimeZoneToUTC = null;
        }
        else {
            $oneHourAgoEndOfHourUserTimeZoneToUTC = $oneHourAgoUserTimeZone->endOfHour()->setTimezone('UTC')->isoFormat('YYYY-MM-DD HH:mm:ss');
        }