Calculate the difference between timezone dates

Question

I need to calculate the difference between 2 dates with different time zone:
The calculation is between the date of posting and the current date.

Assuming a post is from America/Sao_Paulo and another of Europe/Amsterdam.
For each log entry I must keep the user Timezone or the server?

How do I compute the difference when one user is reading another user’s post?
If the São Paulo user accesses the Amsterdam post, how to show that it was the X minutes?

I don’t know the best way to record the input moment of posts...

Answer 1

I suggest you convert to a common Timezone when storing the posting date (server Timezone for example).

When displaying the date to the user, convert the date stored on the server using DateTime

<?php

// String timezone - America/Sao_Paulo exemplo
$timezoneServer = $config['timezoneDefault'];

$date = new DateTime('2014-07-25', new DateTimeZone($timezoneServer));
// Pode-se omitir o segundo parametro para usar o padrão do servidor
// $date = new DateTime('2014-07-25);

// Rotina para recuperar o Timezone do usuário
$userTimezone = $userModel->getUserTimeZone();

// Recupera a data do post e converte para a Timezone do usuário
$postDate = new DateTime($post->date, new DateTimeZone($userTimezone));

// "P" exibe a representação em relação a GMT (-03:00, -02:30)
echo $postDate->format('Y-m-d  H:i:sP');

Answer 2

I suggest you save the logs with the server Timezone and calculate the difference at the time of display (as long as you have saved each user’s Timezone).

• When displaying that the post was X minutes, just calculate the difference between now and the time of posting.
• When displaying the date and time of the post, calculate the difference between the server and user Timezone.

To do this, use the PHP Datetime class (PHP >= 5.2).
Docs.: http://php.net/manual/en/class.datetime.php

Example:

// cria obj com a tz do servidor
$datetime = new DateTime($post->datetime);
// seta a tz do obj com a tz do usuário (isso já converte a datetime do post)
$datetime->setTimezone(new DateTimeZone($user->timezone));
// imprime
echo $datetime->format('d/m/Y H:i');