Timezone: Handle timezones

Indeed, I commented out some timezone lines of code, since it did not seems to be used, yet.
Patches are welcome.

No, I have no vision, yet. But here's a breakdown:

The main use cases would be: OH on users around the globe; OH on entities (restaurants, stores) around the globe.

We have 3 timezones:
1. system timezone
2. user/viewer timezone
3. entity timezone.

Task 1: Where to store the timezone:
1. fetch from another field of the entity?
2. Encode in the OH field?
On first glance, I prefer 1.
[EDIT after reading #10: ]
- fetch from the Time zone field on the same Entity (wich can also be a user)

Task 2: How to show the timezone: This should be configurable per use case
-- do not show/do not use (current situation)
-- show ccs-able subfield with entity's timezone (like 'GMT')
-- show css-able difference (like 'these times are 2 hours earlier then yours')
-- change the times to the user's timezone.
You might need to show the user's timezone in the OH formatter, since most users will not have edited this. Anonymous users can be around the globe, and don't even have the possibility.
Overkill: We can provide some buttons 'set my timezone' ; 'show times in my timezone'; 'show times in local timezone'

Should we use a thirdparty module?
- there is a built-in 'user time zone'
- http://drupal.org/project/tzfield can be added to any entity
- http://drupal.org/project/clock can be used to copy its code to do: "Time zone can be configured as: Site time zone, user time zone, local time zone and custom time zone."

Preferably the timezone is prefilled, depending on an Address in the entity's fields.
- http://drupal.org/project/autotimezone could be adapted to prefill the entity's timezone

linking

Related issues of http://drupal.org/project/tzfield :
#1932968: Set default value to user's timezone
#655032: Does tzfield work with the Date module when displaying event times?

I think it would be extremely useful, to use a Geofield (using the drupal module with the same name) for an entity based timezone. For example, I have a site, that stores the opening hours of many museums all over the world. The nodes representing the museums have a geofield. It would be nice to use that geofield to specify the entities time zone.
I would contribute some code, but maybe we put together our visions and use cases first.

But autodetect timezone of the client with javascript seems not to be a clean solution. The user could be everywhere putting in the office hours for elsewhere. Do you think, it would be useful to add an option to the field settings, that makes it possible to select a geofield, that later can be used for the timezone detection?

You are right! So, I am going to write a patch for the time zone field: http://drupal.org/node/1962888
Is there anybody out there who has started yet to integrate time zone field to office hours?

I think we agree:
- tzfield is the field to store the timezone. (not sure about users, though, which already hve a time zone field)
- Gunwald's idea is OK, to make sure tzfield has the correct value. I've updated #1962888-2: Use geofield to auto set time zone field, Even better, Geofield should add a subfield for this. But that's out of our league.
- Giorgio can now start on that basis.
- I'll just lean back ;-) and test.

So we'll have nodes with the following fields + dataflow:
Addressfield/Location + (Geocoder) + Geofield lat/lon + (new Timezonecoder) + tzfield + (new timezone decoder) + office_hours

That's a long chain! But I guess it's all right.

Add Work Breakdown to summary

I've updated the summary with the text from #3. Feel free to update.

I've made patch, to respect user timezone, when field located in user node.

I am not sure about #13.
Can you explain the use case? It seems it takes the time from the timezone of the owner of the entity, and shows it on the formatter.
It seems this works for smaller websites, but when the website is maintained by several offices, you are not sure about the time.

Patch for D8.

fixed

The basic concept of handling timezone is to save time in UTC format into database and to display the time according to user's time zone. In Drupal 7, you can use format_date() function while saving and displaying time.

We should take into account all 3 instances of timezone in the module. See #2799987: Datetime and Datelist element's timezone handling is fragile, buggy and wrongly documented for a change in core.

Can you explain the use case?

My website is bulletin board. Multiple accounts (clients) with different cities and timezones. Client set his timezone. His articles (offices) has office hours with current status (open\closed). Client set it to e.g. 8-20.
Visitor choose his city and he want to see if offices in this city is opened.

Patch #13 not suite for version D7 1.9 and further, because open status from 1.9 calculates in js.

Fixed.

Shouldn't we check whether the user has set his timezone properly? Or will that handled automatically?

@johnvNo, user timezone check performs.

Fixed.

Some changes because of patches conflict.

I added hook_office_hours_isopen_time_alter() to alter current time in IsOpen() method.

Thank you @hswong3i.
Well done! I've already started fixing patch but you were the first :)

@super_romeo, @hswong3i,
let me make your life a bit simpler.

I committed the patch/merge request:
- isolating the 2 hooks in a central function
- adding a missing piece of code in api.php file
- sorry for renaming the hook to: hook_office_hours_current_time_alter, since that is what happening: you change the 'current' time, in order to change the isOpen indicator (and Current day formatter).

@super_romeo, I added your use case to the api.php file:
// Use case is a website as bulletin board.
// Multiple accounts (clients) with different cities and timezones.
// Client sets his timezone in his account data.
// His articles (offices) have office hours with current status (open\closed).
// Client sets it to e.g., 8:00-20:00.
// Visitor chooses his city and wants to see if offices in this city are open.

Regarding the client and visitor:
// Client sets his timezone in his account data. <-- is this true? I assumed it.
// Visitor chooses his city <-- How? in his account, or in a view? Does visitor set the time zone, too?

So, keeping the ticket open for full functionality. Please check the committed code.
Also please test the getCacheTime(), since it (max-age') may be wrong.

Thank you @johnv!

Client sets his timezone in his account data. <-- is this true?

Yes. It's is in registration form and I get it as $account->getTimeZone().

/**
 * Implements hook_office_hours_isopen_time_alter().
 */
function rg_opened_office_hours_isopen_time_alter(
  int &$time,
  EntityInterface $entity
) {
  // Assume that all owned entities (for example, offices and ad) should
  // depends on user timezone. Add user timezone to time.
  if ($entity instanceof \Drupal\user\EntityOwnerInterface
    && ($account = $entity->getOwner())
    && ($account->isAuthenticated())
  ) {
    $time += RgOpenedHelper::getTimezoneOffset($account->getTimeZone());
  }
}

Visitor chooses his city <-- How?

In a view's filter.

Does visitor set the time zone, too?

No. Each city has assigned time zone value.
Then in my custom view's filter I add time condition to query.

Thanks, updated the comments.