从时间戳中减去用户TimeZone偏移量（例如+02：00）

Question

Background:

I am displaying a list of times as an associative array. The array looks like this (11:00 AM to 12:00 AM):

array(5) {
  [1475226000]=>
  string(35) "September 30, 2016, 11:00 am +02:00"
  [1475226900]=>
  string(35) "September 30, 2016, 11:15 am +02:00"
  [1475227800]=>
  string(35) "September 30, 2016, 11:30 am +02:00"
  [1475228700]=>
  string(35) "September 30, 2016, 11:45 am +02:00"
  [1475229600]=>
  string(35) "September 30, 2016, 12:00 pm +02:00"
}

The key is a unix timestamp. The value is the formatted unix timestamp displayed in the users time zone.

My Code

Here is my commented class that generates the array:

<?php

class Time
{
    public function __construct()
    {
        date_default_timezone_set('UTC');
    }

    public function getTimeSlots($year, $month, $day, $start_time = '11:00', $end_time = '12:00')
    {
        $date = $year . '-' .  $month . '-' . $day;
        // get GMT timestamp of 2016-09-30 00:00 Europe/London
        $gmt_date = strtotime($this->getRelativeDateTime($date));

        $gmt_date = $gmt_date - 7200;
        // subtract from or add to $gmt_date whatever our timezone offset in hours is

        // get start time offset in seconds from 2016-9-30 00:00
        $seconds_start = strtotime('1970-01-01 ' . $start_time . ' UTC');
        // get end time offset in seconds from 2016-9-30 00:00
        $seconds_end   = strtotime('1970-01-01 ' . $end_time . ' UTC');

        $unix_seconds_start = $gmt_date + $seconds_start; // GMT
        $unix_seconds_end   = $gmt_date + $seconds_end;

        // echo $unix_seconds_start . date('Y-m-d H:i', $unix_seconds_start);
        // echo '<br>';
        // echo $unix_seconds_end . date('Y-m-d H:i', $unix_seconds_end);

        while ($unix_seconds_start <= $unix_seconds_end) {

            $dt = new DateTime('@' . $unix_seconds_start);
            $dt->setTimezone(new DateTimeZone('Europe/Paris'));
            $slots[$unix_seconds_start] = $dt->format('F j, Y, H:i a P');
            $unix_seconds_start = $unix_seconds_start + 900;

        }
        echo '<pre>', var_dump($slots), '</pre>';
    }

    public function getRelativeDateTime($date)
    {
        $date = new DateTime($date, new DateTimeZone('Europe/Paris'));
        return $date->format('Y-m-d H:i');
    }
}

$time = new Time;
$time->getTimeSlots('2016', '09', '30');

// we want var_dump to show the following
// --------------------------------------
//
// array () {
//     from 00:00
//     1234567890 (unix timestamp) => '00:00' (users time)
//     1234567890 (unix timestamp) => '00:15' (users time)
//     1234567890 (unix timestamp) => '00:30' (users time)
//     1234567890 (unix timestamp) => '00:45' (users time)
//     to  24:00
// }

Issue

I want my times to start strictly at 00:00 AM and end at 24:00pm for the user, however as you can see if you run the code I am getting an offset depending on my users time offset.

That means if the user has his time zone as Europe/London +01:00 my array starts at 01:00.

The problem is on line 16. As you can see if you uncomment line 16 and run the code it works but only because I am explicitly subtracting two hours (in seconds) from the timestamp.

http://sandbox.onlinephpfunctions.com/code/d19b6fc5335f41af491dfedcfae2c390aa3000ec

Question

Is there a way using DateTime (or any other method!) to subtract the users time zone offset from the $gmt_date variable?

Answer 1

This is your answer. Use DateTime object and create a timezone.

<?php

$tz_array = array('UTC', 'Europe/Paris', 'Asia/Jerusalem');

foreach ($tz_array as $tz) {
    $time = new Time($tz);
    $time->getTimeSlots('2016', '09', '30');
}

class Time {

    /** @var DateTimeZone */
    private $tz;

    public function __construct($tz) {
        $this->tz = new DateTimeZone($tz);
    }

    public function getTimeSlots($year, $month, $day, $start_time = '11:00', $end_time = '12:00') {

        $from = new DateTime("$year-$month-$day $start_time:00", $this->tz);
        $to = new DateTime("$year-$month-$day $end_time:00", $this->tz);

        $unix_seconds_start = $from->getTimestamp();
        $unix_seconds_end = $to->getTimestamp();

        $interval = new DateInterval('PT900S'); // 900 seconds interval

        $slots = array();

        while ($unix_seconds_start <= $unix_seconds_end) {

            $slots[$unix_seconds_start] = $from->format('F j, Y, H:i a P');
            $from->add($interval);
            $unix_seconds_start = $from->getTimestamp();
        }

        echo
        "Time slots demo for timezone ",
        $this->tz->getName();
        var_dump($slots);
    }

}