Data.Time.LocalTime.TimeZone.Detect

Exposes utilities derived from the excellent ZoneDetect library https://github.com/BertoldVdb/ZoneDetect. To use this module, you need to obtain database files from the aforementioned library's server.

Additionally, if you have a local time, latitude and longitude, we use the timezone-series and timezone-olson packages to help determine the equivalent UTC instant to that point in geography and time.

The only relevant binding to ZoneDetect is lookupTimeZoneName, richer information that plays neatly with the notion of TimeZone could be derived, but I didn't have a personal need for that yet.

Documentation

lookupTimeZoneName :: MonadFail m => FilePath -> Double -> Double -> m TimeZoneName

Given a timezone database, latitude and longitude, try to determine the timezone name. Follow the instructions in the C library's repository to obtain timezone database files (https://github.com/BertoldVdb/ZoneDetect/tree/05567e367576d7f3efa00083b7661a01e43dc8ca/database) Once in possesion of said files, the lookup looks as follows:

>>> tz <- lookupTimeZoneName "./test/tz_db/timezone21.bin" 40.7831 (-73.9712) :: Maybe TimeZoneName
Just "America/New_York"

An invalid database file, or invalid coordinates, will cause the given monad to fail.

timeAtPointToUTC :: FilePath -> Double -> Double -> LocalTime -> IO UTCTime

Given a timezone database, latitude, longitude and a local reference time, find the UTC Time equivalent of that reference time in the given timezone. The reference time helps determine which offset was in effect, since daylight savings, historical circumstances, political revisions and other circumstances (documented in the olson tz database) may have been in effect at that point in spacetime.

timeInTimeZoneToUTC :: TimeZoneName -> LocalTime -> IO UTCTime

Given a timezone name (presumably obtained via lookupTimeZoneName,) and a reference time in LocalTime, find the UTC equivalent.

getTimeZoneSeriesFromOlsonFileUNIX :: TimeZoneName -> IO TimeZoneSeries

Gets timezone info from the standard location in UNIX systems. The name should be one of the standard tz database names, as returned by lookupTimeZoneName. See: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones

type TimeZoneName = FilePath

Alias for clarity, timezones are path-like strings that follow the IANA conventions documented here: https://data.iana.org/time-zones/tz-link.html and here: https://en.wikipedia.org/wiki/Tz_database#Names_of_time_zones