TZInfo - Ruby Timezone Library
==============================

[TZInfo](http://tzinfo.github.io) provides daylight savings aware 
transformations between times in different timezones.


Data Sources
------------

TZInfo requires a source of timezone data. There are two built-in options:

1. The TZInfo::Data library (the tzinfo-data gem). TZInfo::Data contains a set 
   of Ruby modules that are generated from the [IANA Time Zone Database](http://www.iana.org/time-zones).
2. A zoneinfo directory. Most Unix-like systems include a zoneinfo directory 
   containing timezone definitions. These are also generated from the 
   [IANA Time Zone Database](http://www.iana.org/time-zones).

By default, TZInfo::Data will be used. If TZInfo::Data is not available (i.e. 
if require 'tzinfo/data' fails), then TZInfo will search for a zoneinfo
directory instead (using the search path specified by 
TZInfo::ZoneinfoDataSource::DEFAULT_SEARCH_PATH).

If no data source can be found, a TZInfo::DataSourceNotFound exception will be
raised when TZInfo is used.

The default data source selection can be overridden using 
TZInfo::DataSource.set.

Custom data sources can also be used. See TZInfo::DataSource.set for
further details.


Installation
------------

The TZInfo gem can be installed by running:

    gem install tzinfo

To use the Ruby modules as the data source, TZInfo::Data will also need to be
installed:

    gem install tzinfo-data
  

Example Usage
-------------

The following code will obtain the America/New_York timezone (as an instance
of TZInfo::Timezone) and covert a time in UTC to local New York time:

    require 'tzinfo'
    
    tz = TZInfo::Timezone.get('America/New_York')
    local = tz.utc_to_local(Time.utc(2005,8,29,15,35,0))

Note that the local Time returned will have a UTC timezone (local.zone will 
return "UTC"). This is because the Ruby Time class only supports two timezones: 
UTC and the current system local timezone.
  
To convert from a local time to UTC, the local_to_utc method can be used as
follows:

    utc = tz.local_to_utc(local)

Note that the timezone information of the local Time object is ignored (TZInfo
will just read the date and time and treat them as if there were in the 'tz'
timezone). The following two lines will return the same result regardless of 
the system's local timezone:

    tz.local_to_utc(Time.local(2006,6,26,1,0,0))
    tz.local_to_utc(Time.utc(2006,6,26,1,0,0))
  
To obtain information about the rules in force at a particular UTC or local 
time, the TZInfo::Timezone.period_for_utc and TZInfo::Timezone.period_for_local
methods can be used. Both of these methods return TZInfo::TimezonePeriod 
objects. The following gets the identifier for the period (in this case EDT).

    period = tz.period_for_utc(Time.utc(2005,8,29,15,35,0))
    id = period.zone_identifier
  
The current local time in a Timezone can be obtained with the 
TZInfo::Timezone#now method:

    now = tz.now

All methods in TZInfo that operate on a time can be used with either Time or 
DateTime instances or with Integer timestamps (i.e. as returned by Time#to_i). 
The type of the values returned will match the the type passed in.

A list of all the available Timezone identifiers can be obtained using the
TZInfo::Timezone.all_identifiers method. TZInfo::Timezone.all can be called
to get an Array of all the TZInfo::Timezone instances.

Timezones can also be accessed by country (using an ISO 3166-1 alpha-2 country 
code). The following code retrieves the TZInfo::Country instance representing 
the USA (country code 'US') and then gets all the Timezone identifiers used in 
the USA.

    us = TZInfo::Country.get('US')
    timezones = us.zone_identifiers
  
The TZInfo::Country#zone_info method provides an additional description and 
geographic location for each Timezone in a Country.

A list of all the available country codes can be obtained using the
TZInfo::Country.all_codes method. TZInfo::Country.all can be called to get an 
Array of all the Country instances.
  
For further detail, please refer to the API documentation for the 
TZInfo::Timezone and TZInfo::Country classes.


Thread-Safety
-------------

The TZInfo::Country and TZInfo::Timezone classes are thread-safe. It is safe to 
use class and instance methods of TZInfo::Country and TZInfo::Timezone in 
concurrently executing threads. Instances of both classes can be shared across 
thread boundaries.


Documentation
-------------

API documentation for TZInfo is available on [RubyDoc.info](http://rubydoc.info/gems/tzinfo/frames).


License
-------

TZInfo is released under the MIT license, see LICENSE for details.


Source Code
-----------

Source code for TZInfo is available on [GitHub](https://github.com/tzinfo/tzinfo).


Issue Tracker
-------------

Please post any bugs, issues, feature requests or questions to the 
[GitHub issue tracker](https://github.com/tzinfo/tzinfo/issues).
