To datetime with timezone

[jadlr]

This changes the behavior of to_datetime when called with a DateTime struct.

I'm writing an application that needs to convert datetimes to other timezones and I didn't know about Timex.Timezone.convert/2

I was surprised by the current behavior:

iex(1)> Timex.to_datetime(Timex.now, "Europe/Berlin") 
#<DateTime(2016-10-11T16:05:08.439973Z Etc/UTC)>

I was even more surprised by:

iex(2)> Timex.to_datetime(Timex.now, "Hello")        
#<DateTime(2016-10-11T16:05:45.608048Z Etc/UTC)>

I think the more logical thing to do is to convert the date if the timezone differs from the one in the DateTime struct.

What do you think? Is there something I am overlooking?

[coveralls]

Coverage increased (+0.01%) to 64.812% when pulling 6ed44ee on trsc:to_datetime_with_timezone into f0f1753 on bitwalker:master.

[bitwalker]

You can just do to_datetime(%DateTime{time_zone: timezone} = d, timezone), do: d which will only match if both the provided timezone and the one on the DateTime are the same.

[bitwalker]

You're definitely correct, your changes look good except for the one tweak I suggested. I'll get this merged once that's updated. Thanks for the PR!

[coveralls]

Coverage increased (+0.01%) to 64.812% when pulling 6b0fe32 on trsc:to_datetime_with_timezone into f0f1753 on bitwalker:master.

[coveralls]

Coverage increased (+0.01%) to 64.812% when pulling 6b0fe32 on trsc:to_datetime_with_timezone into f0f1753 on bitwalker:master.

[jadlr]

@bitwalker thanks for the hint! I didn't know that.

I just found out that Timex.Timezone.convert can return an AmbiguousDateTime. Could that be a problem? Should I add AmbiguousDateTime to the @spec of to_datetime?

[bitwalker]

Yeah could you add it to the @spec, it should be there. AmbiguousDateTime is intended to be resolved by the caller, but it should only occur with DateTime, no other types, so we need to pass it back to the caller for any conversions like this which may result in an AmbiguousDateTime.

[coveralls]

Coverage increased (+0.01%) to 64.812% when pulling da9513f on trsc:to_datetime_with_timezone into f0f1753 on bitwalker:master.

[jadlr]

@bitwalker OK, done

[bitwalker]

Thanks again!