On the backend (phoenix app) I have a situation where I am creating Events with a start_date. Every event will have one Location known in advance, with geo (lat lng) coordinates. A concert or sports event for example.

On the client side, rather than ask the user for a time zone directly, I decided that it would be cool to extract that info using the location coords and Google Maps Time Zone API (Get Started  |  Time Zone API  |  Google for Developers).

You pass the coordinates of a location (lat, lng) and a unix timestamp, and it returns the tz name, utc offset, dst offset.

Here is my idea for how it would work:

The user submitted start_date is a NaiveDateTime representing the local/wall time of the event. However the Google API expects the timestamp as unix, which is essentially UTC if I’m correct. So my thinking is that could send the unix current time to the Time Zone API to get the locations timezone. Then use a library like Calendar or Timex to apply this timezone with the naive datetime, to generate a correct DateTime.

It seems a little like going round the houses though . I did think I could query the location after it’s first created and save the timezone alongside it, but not sure if that would be a bad idea when dealing with tz data.

Any feedback on this flow would be greatly appreciated!