mweibel / timex

Easy to use Date and Time modules for Elixir

Date & Time modules for Elixir

Status

Version 0.4.5 is stable and usable on Elixir 0.12.4 and 0.13+. However, future development is happening on the 0.5.0 branch, where I'm making a number of significant changes:

• Requiring Elixir 0.13+
• Moving away from records to structs/maps
• Creating seperate Date, Time, DateTime and Timezone structs (no more TimezoneInfo; Date will contain only year/month/day/calendar; Time will contain hours/mins/seconds/ms/us; DateTime will be composed of a Date struct, a Time struct, and a Timezone struct.
• Moving the primary API interface from Date to DateTime
• Removing, improving, and potentially adding new functions to work with these new changes.

The goal after 0.5.0 releases is for this to be a stable API with the goal of being merged in to the language at some future date if it turns out that it solves the problems needed for inclusion in the standard lib.

---

To use timex with your projects, edit your mix.exs file and add it as a dependency:

defp deps do
  [{:timex, github: "bitwalker/timex"}]
end

After that, run mix deps.get to load the dependency. To use Timex modules without the Timex namespace, add use Timex to the top of each module you plan on referencing Timex from. You can then reference the modules directly, for example: Date.now(), versus Timex.Date.now(). This is for compatibility with other libraries which might define their own Date/DateTime/Time implementations.

Overview

This is a draft implementation of a Date/Time library for Elixir that will deal with all aspects of working with dates and time intervals.

Basically, the Date module is for dealing with dates. It supports getting current date in any time zone, converting between timezones while taking Daylight Savings Time offsets into account, calculating time intervals between two dates, shifting a date by some amount of seconds/hours/days/years towards past and future, etc. As Erlang provides support only for the Gregorian calendar, that's what timex currently supports, but it is possible to add additional calendars if needed.

The Time module supports a finer grain level of calculations over time intervals. It is going to be used for timestamps in logs, measuring code executions times, converting time units, and so forth.

Use cases

Getting current date

Get current date in the local time zone.

date = Date.local
DateFormat.format!(date, "{ISO}")      #=> "2013-09-30T16:40:08+0300"
DateFormat.format!(date, "{RFC1123}")  #=> "Mon, 30 Sep 2013 16:40:08 EEST"
DateFormat.format!(date, "{kitchen}")  #=> "4:40PM"

The date value that Date produced encapsulates current date, time, and time zone information. This allows for great flexibility without any overhead on the user's part.

Since Erlang's native date format doesn't carry any time zone information, Date provides a bunch of constructors that take Erlang's date value and an optional time zone.

datetime = {{2013,3,17},{21,22,23}}

date = Date.from(datetime)           # datetime is assumed to be in UTC by default
DateFormat.format!(date, "{RFC1123}")   #=> "Sun, 17 Mar 2013 21:22:23 GMT"

date = Date.from(datetime, :local)   # indicates that datetime is in local time zone
DateFormat.format!(date, "{RFC1123}")   #=> "Sun, 17 Mar 2013 21:22:23 CST"

Date.local(date)  # convert date to local time zone (CST for our example)
#=> %DateTime{year: 2013, month: 3, day: 17, hour: 15, minute: 22, second: 23, timezone: ...}

# Let's see what happens if we switch the time zone
date = Date.set(date, tz: Timezone.get("EST"))
DateFormat.format!(date, "{RFC1123}")
#=> "Sun, 17 Mar 2013 17:22:23 EST"

Date.universal(date)  # convert date to UTC
#=> %DateTime{year: 2013, month: 3, day: 17, hour: 21, minute: 22, second: 23, timezone: ...}

Working with time zones

date = Date.from({2013,1,1}, Date.timezone("America/Chicago"))
DateFormat.format!(date, "{ISO}")
#=> "2013-01-01T00:00:00-0600"
DateFormat.format!(date, "{ISOz}")
#=> "2013-01-01T06:00:00Z"

DateFormat.format!(date, "{RFC1123}")
#=> "Tue, 01 Jan 2013 00:00:00 CST"

date = Date.now
# Convert to UTC
Date.universal(date)                        #=> %DateTime{...}
# Convert a date to local time
Date.local(date)                            #=> %DateTime{...}
# Convert a date to local time, and provide the local timezone
Date.local(date, Date.timezone("PST"))      #=> %DateTime{...}

Extracting information about dates

Find out current weekday, week number, number of days in a given month, etc.

date = Date.now
DateFormat.format!(date, "{RFC1123}")
#=> "Wed, 26 Feb 2014 06:02:50 GMT"

Date.weekday(date)           #=> 3
Date.iso_week(date)          #=> {2014, 9}
Date.iso_triplet(date)       #=> {2014, 9, 3}

Date.days_in_month(date)     #=> 28
Date.days_in_month(2012, 2)  #=> 29

Date.is_leap?(date)           #=> false
Date.is_leap?(2012)           #=> true

Date.day_to_num(:mon)         #=> 1
Date.day_to_num("Thursday")   #=> 4 (can use Thursday, thursday, Thu, thu, :thu)
Date.day_name(4)              #=> "Thursday"

Date.month_to_num(:apr)       #=> 4 (same as day_to_num with possible formats)
Date.month_name(4)            #=> "April"

Date arithmetic

Date can convert dates to time intervals since UNIX epoch or year 0. Calculating time intervals between two dates is possible via the diff() function (not implemented yet).

date = Date.now
DateFormat.format!(date, "{RFC1123}")
#=> "Mon, 30 Sep 2013 16:55:02 EEST"

Date.convert(date, :secs)  # seconds since Epoch
#=> 1380549302

Date.to_sec(date, :zero)  # seconds since year 0
#=> 63547768502

DateFormat.format!(Date.epoch(), "{ISO}")
#=> "1970-01-01T00:00:00+0000"

Date.epoch(:secs)  # seconds since year 0 to Epoch
#=> 62167219200

date = Date.from(Date.epoch(:secs) + 144, :secs, :zero)  # :zero indicates year 0
DateFormat.format!(date, "{ISOz}")
#=> "1970-01-01T00:02:24Z"

Shifting dates

Shifting refers to moving by some amount of time towards past or future. Date supports multiple ways of doing this.

date = Date.now
DateFormat.format!(date, "{RFC1123}")
#=> "Mon, 30 Sep 2013 16:58:13 EEST"

DateFormat.format!( Date.shift(date, secs: 78), "{RFC1123}" )
#=> "Mon, 30 Sep 2013 16:59:31 EEST"

DateFormat.format!( Date.shift(date, secs: -1078), "{RFC1123}" )
#=> "Mon, 30 Sep 2013 16:40:15 EEST"

DateFormat.format!( Date.shift(date, days: 1), "{RFC1123}" )
#=> "Tue, 01 Oct 2013 16:58:13 EEST"

DateFormat.format!( Date.shift(date, weeks: 3), "{RFC1123}" )
#=> "Mon, 21 Oct 2013 16:58:13 EEST"

DateFormat.format!( Date.shift(date, years: -13), "{RFC1123}" )
#=> "Sat, 30 Sep 2000 16:58:13 EEST"

Working with Time module

The Time module already has some conversions and functionality for measuring time.

## Time.now returns time since UNIX epoch ##

Time.now
#=> {1362,781057,813380}

Time.now(:secs)
#=> 1362781082.040016

Time.now(:msecs)
#=> 1362781088623.741


## Converting units is easy ##

t = Time.now
#=> {1362,781097,857429}

Time.to_usecs(t)
#=> 1362781097857429.0

Time.to_secs(t)
#=> 1362781097.857429

Time.to_secs(13, :hours)
#=> 46800

Time.to_secs(13, :msecs)
#=> 0.013


## We can also convert from timestamps to other units using a single function ##

Time.convert(t, :secs)
#=> 1362781097.857429

Time.convert(t, :mins)
#=> 22713018.297623817

Time.convert(t, :hours)
#=> 378550.30496039696


## elapsed() calculates time interval between now and t ##

Time.elapsed(t)
#=> {0,68,-51450}

Time.elapsed(t, :secs)
#=> 72.100247

t1 = Time.elapsed(t)
#=> {0,90,-339935}


## diff() calculates time interval between two timestamps ##

Time.diff(t1, t)
#=> {-1362,-781007,-1197364}

Time.diff(Time.now, t)
#=> {0,105,-300112}

Time.diff(Time.now, t, :hours)
#=> 0.03031450388888889

Converting time units

dt = Time.now
Time.convert(dt, :secs)
Time.convert(dt, :mins)
Time.convert(dt, :hours)
Time.to_timestamp(13, :secs)

FAQ

Which functions provide microsecond precision?

If you need to work with time intervals down to microsecond precision, you should take a look at the functions in the Time module. The Date module is designed for things like handling different time zones and working with dates separated by large intervals, so the minimum time unit it uses is seconds.

So how do I work with time intervals defined with microsecond precision?

Use functions from the Time module for time interval arithmetic.

How do I find the time interval between two dates?

Use Date.diff to obtain the number of seconds, minutes, hours, days, months, weeks, or years between two dates.

What kind of operations is this lib going to support eventually?

The goal is to make it so you never have to use Erlang's calendar/time functions.

Some inspirations I'm currently drawing from:

• Moment.js
• JodaTime

What is the support for time zones?

Full support for retreiving local timezone configuration on OSX, *NIX, and Windows, conversion to any timezone in the Olson timezone database, and full support for daylight savings time transitions.

Timezone support is also exposed via the Timezone, Timezone.Local, and Timezone.Dst modules. Their functionality is exposed via the Date module's API, and most common use cases shouldn't need to access the Timezone namespace directly, but it's there if needed.

License

This software is licensed under the MIT license.