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A simple way to get accurate current and historical timezone information based on zone or latitude and longitude coordinates. This gem uses the tz database (http://www.twinsun.com/tz/tz-link.htm) for historical timezone information. It also uses the geonames API for timezone latitude and longitude lookup (http://www.geonames.org/export/web-servi…
Ruby
branch: master

README.markdown

Timezone

A simple way to get accurate current and historical timezone information based on zone or latitude and longitude coordinates. This gem uses the tz database for historical timezone information. It also uses the geonames API or the Google Timezone API for timezone latitude and longitude lookup.

Installation

Add the following to your Gemfile:

gem 'timezone'

Then install your bundle.

bundle install

Getting Started

Getting the current time or any historical time in any timezone, with daylight savings time taken into consideration, is easy:

timezone = Timezone::Zone.new :zone => 'America/Los_Angeles'

timezone.time(Time.now)
=> 2011-02-11 17:29:05 UTC

timezone.time(Time.utc(2010, 1, 1, 0, 0, 0))
=> 2009-12-31 16:00:00 UTC

timezone.time_with_offset(Time.utc(2010,1,1,0,0,0))
=> 2009-12-31 16:00:00 -0800

Time is always returned in the UTC timezone when using the time function, but it accurately reflects the actual time in the specified timezone. The reason for this is that this function also takes into account daylight savings time and historical changes in timezone, which can alter the offset. If you want a time with the appropriate offset at the given time, then use the time_with_offset function as shown above.

You can use the timezone object to convert local times into the best UTC estimate. The reason this is an estimate is that some local times do not actually map to UTC times (for example when time jumps forward) and some local times map to multiple UTC times (for example when time falls back).

timezone = Timezone::Zone.new :zone => 'America/Los_Angeles'

timezone.local_to_utc(Time.utc(2015,11,1,1,50,0))
=> 2015-11-01 08:50:00 UTC

You can also query a Timezone::Zone object to determine if it was in Daylight Savings Time:

timezone = Timezone::Zone.new :zone => 'America/Los_Angeles'
timezone.dst?(Time.now)
=> true
timezone.dst?(Time.utc(2010, 1, 1, 0, 0, 0))
=> false

Getting the timezone for a specific latitude and longitude

First, make sure you have a geonames username. It's free and easy to setup, you can do so here.

Second, add the following to your application.rb file, or before you perform a coordinate lookup.

Timezone::Configure.begin do |c|
  c.username = 'your_geonames_username_goes_here'
end

Alternatively, timezone can be used with a Google api key, which you can get here.

Next, add the following to your application.rb file, or before you perform a coordinate lookup.

Timezone::Configure.begin do |c|
  c.google_api_key = 'your_google_api_key_goes_here'
  c.google_client_id = 'your_google_client_id' # only if using 'Google for Work'
end

Finally, for either geonames or Google implementation, pass the coordinates to your timezone initialization function.

timezone = Timezone::Zone.new :latlon => [-34.92771808058, 138.477041423321]
timezone.zone
=> "Australia/Adelaide"
timezone.time Time.now
=> 2011-02-12 12:02:13 UTC

Displaying a timezone's name in a Rails/ActiveSupport compatible format

timezone = Timezone::Zone.new :latlon => [-34.92771808058, 138.477041423321]
timezone.active_support_time_zone
=> "Eastern Time (US & Canada)"

Getting the complete list of timezones.

Retrieving the complete list of timezones is quite simple:

timezones = Timezone::Zone.names
=> ["Africa/Abidjan", "Africa/Accra", "Africa/Addis_Ababa", "Africa/Algiers", ...]

Listing current information from specific timezones

If you need information from a specific set of timezones rather than a complete list or one at a time, this can be accomplished with the following:

zone_list = Timezone::Zone.list "America/Chicago", "America/New_York", "America/Boise"
# This will return an array of information hashes in the following format:
# {
#   :zone => "America/Chicago",
#   :title => "America/Chicago", # this can be customized to your needs
#   :offset => -18000, # UTC offset in seconds
#   :utc_offset => -5, # UTC offset in hours
#   :dst => false
# }

You can customize what is placed in the :title key in the configuration block. This would be useful in the case of an HTML select list that you would like to display different values than the default name. For example, the following configuration will set the :title key in the list hash to "Chicago" rather than "America/Chicago".

Timezone::Configure.build do |c|
  c.replace "America/Chicago", with: "Chicago"
end

Also, if you make numerous calls to the Zone#list method in your software, but you would like to avoid duplicating which timezones to retrieve, you can set a default in the configuration:

Timezone::Configure.begin do |c|
  c.default_for_list = "America/Chicago", "America/New_York", "Australia/Sydney"
end

Finally, by default the Zone#list method will order the results by the timezone's UTC offset. You can customize this behavior this way:

Timezone::Configure.begin do |c|
  # this can equal any hash key returned by the Zone#list method
  c.order_list_by = :title
end

Using Your Own HTTP Client

If you have non-standard http request needs or want to have more control over API calls to Geonames and Google, you can write your own very simple http client wrapper instead of using the built-in default. Be aware that the Google timezone API uses https protocol.

class MyHTTPClient
  def initialize(protocol, host)
  end

  # Return a response object that responds to #body and #code
  def get(url)
  end
end

Timezone::Configure.begin do |c|
  c.http_client = MyHTTPClient
end

For an example, see Timezone::NetHTTPClient which uses the standard Net::HTTP library to perform API calls.

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