time_zone.rb

class TimeZone
  unless const_defined?(:MAPPING)
    # Keys are Rails TimeZone names, values are TZInfo identifiers
    MAPPING = {
      "International Date Line West" => "Pacific/Midway",
      "Midway Island"                => "Pacific/Midway",
      "Samoa"                        => "Pacific/Pago_Pago",
      "Hawaii"                       => "Pacific/Honolulu",
      "Alaska"                       => "America/Juneau",
      "Pacific Time (US & Canada)"   => "America/Los_Angeles",
      "Tijuana"                      => "America/Tijuana",
      "Mountain Time (US & Canada)"  => "America/Denver",
      "Arizona"                      => "America/Phoenix",
      "Chihuahua"                    => "America/Chihuahua",
      "Mazatlan"                     => "America/Mazatlan",
      "Central Time (US & Canada)"   => "America/Chicago",
      "Saskatchewan"                 => "America/Regina",
      "Guadalajara"                  => "America/Mexico_City",
      "Mexico City"                  => "America/Mexico_City",
      "Monterrey"                    => "America/Monterrey",
      "Central America"              => "America/Guatemala",
      "Eastern Time (US & Canada)"   => "America/New_York",
      "Indiana (East)"               => "America/Indiana/Indianapolis",
      "Bogota"                       => "America/Bogota",
      "Lima"                         => "America/Lima",
      "Quito"                        => "America/Lima",
      "Atlantic Time (Canada)"       => "America/Halifax",
      "Caracas"                      => "America/Caracas",
      "La Paz"                       => "America/La_Paz",
      "Santiago"                     => "America/Santiago",
      "Newfoundland"                 => "America/St_Johns",
      "Brasilia"                     => "America/Argentina/Buenos_Aires",
      "Buenos Aires"                 => "America/Argentina/Buenos_Aires",
      "Georgetown"                   => "America/Argentina/San_Juan",
      "Greenland"                    => "America/Godthab",
      "Mid-Atlantic"                 => "Atlantic/South_Georgia",
      "Azores"                       => "Atlantic/Azores",
      "Cape Verde Is."               => "Atlantic/Cape_Verde",
      "Dublin"                       => "Europe/Dublin",
      "Edinburgh"                    => "Europe/Dublin",
      "Lisbon"                       => "Europe/Lisbon",
      "London"                       => "Europe/London",
      "Casablanca"                   => "Africa/Casablanca",
      "Monrovia"                     => "Africa/Monrovia",
      "UTC"                          => "Etc/UTC",
      "Belgrade"                     => "Europe/Belgrade",
      "Bratislava"                   => "Europe/Bratislava",
      "Budapest"                     => "Europe/Budapest",
      "Ljubljana"                    => "Europe/Ljubljana",
      "Prague"                       => "Europe/Prague",
      "Sarajevo"                     => "Europe/Sarajevo",
      "Skopje"                       => "Europe/Skopje",
      "Warsaw"                       => "Europe/Warsaw",
      "Zagreb"                       => "Europe/Zagreb",
      "Brussels"                     => "Europe/Brussels",
      "Copenhagen"                   => "Europe/Copenhagen",
      "Madrid"                       => "Europe/Madrid",
      "Paris"                        => "Europe/Paris",
      "Amsterdam"                    => "Europe/Amsterdam",
      "Berlin"                       => "Europe/Berlin",
      "Bern"                         => "Europe/Berlin",
      "Rome"                         => "Europe/Rome",
      "Stockholm"                    => "Europe/Stockholm",
      "Vienna"                       => "Europe/Vienna",
      "West Central Africa"          => "Africa/Algiers",
      "Bucharest"                    => "Europe/Bucharest",
      "Cairo"                        => "Africa/Cairo",
      "Helsinki"                     => "Europe/Helsinki",
      "Kyev"                         => "Europe/Kiev",
      "Riga"                         => "Europe/Riga",
      "Sofia"                        => "Europe/Sofia",
      "Tallinn"                      => "Europe/Tallinn",
      "Vilnius"                      => "Europe/Vilnius",
      "Athens"                       => "Europe/Athens",
      "Istanbul"                     => "Europe/Istanbul",
      "Minsk"                        => "Europe/Minsk",
      "Jerusalem"                    => "Asia/Jerusalem",
      "Harare"                       => "Africa/Harare",
      "Pretoria"                     => "Africa/Johannesburg",
      "Moscow"                       => "Europe/Moscow",
      "St. Petersburg"               => "Europe/Moscow",
      "Volgograd"                    => "Europe/Moscow",
      "Kuwait"                       => "Asia/Kuwait",
      "Riyadh"                       => "Asia/Riyadh",
      "Nairobi"                      => "Africa/Nairobi",
      "Baghdad"                      => "Asia/Baghdad",
      "Tehran"                       => "Asia/Tehran",
      "Abu Dhabi"                    => "Asia/Muscat",
      "Muscat"                       => "Asia/Muscat",
      "Baku"                         => "Asia/Baku",
      "Tbilisi"                      => "Asia/Tbilisi",
      "Yerevan"                      => "Asia/Yerevan",
      "Kabul"                        => "Asia/Kabul",
      "Ekaterinburg"                 => "Asia/Yekaterinburg",
      "Islamabad"                    => "Asia/Karachi",
      "Karachi"                      => "Asia/Karachi",
      "Tashkent"                     => "Asia/Tashkent",
      "Chennai"                      => "Asia/Kolkata",
      "Kolkata"                      => "Asia/Kolkata",
      "Mumbai"                       => "Asia/Kolkata",
      "New Delhi"                    => "Asia/Kolkata",
      "Kathmandu"                    => "Asia/Katmandu",
      "Astana"                       => "Asia/Dhaka",
      "Dhaka"                        => "Asia/Dhaka",
      "Sri Jayawardenepura"          => "Asia/Dhaka",
      "Almaty"                       => "Asia/Almaty",
      "Novosibirsk"                  => "Asia/Novosibirsk",
      "Rangoon"                      => "Asia/Rangoon",
      "Bangkok"                      => "Asia/Bangkok",
      "Hanoi"                        => "Asia/Bangkok",
      "Jakarta"                      => "Asia/Jakarta",
      "Krasnoyarsk"                  => "Asia/Krasnoyarsk",
      "Beijing"                      => "Asia/Shanghai",
      "Chongqing"                    => "Asia/Chongqing",
      "Hong Kong"                    => "Asia/Hong_Kong",
      "Urumqi"                       => "Asia/Urumqi",
      "Kuala Lumpur"                 => "Asia/Kuala_Lumpur",
      "Singapore"                    => "Asia/Singapore",
      "Taipei"                       => "Asia/Taipei",
      "Perth"                        => "Australia/Perth",
      "Irkutsk"                      => "Asia/Irkutsk",
      "Ulaan Bataar"                 => "Asia/Ulaanbaatar",
      "Seoul"                        => "Asia/Seoul",
      "Osaka"                        => "Asia/Tokyo",
      "Sapporo"                      => "Asia/Tokyo",
      "Tokyo"                        => "Asia/Tokyo",
      "Yakutsk"                      => "Asia/Yakutsk",
      "Darwin"                       => "Australia/Darwin",
      "Adelaide"                     => "Australia/Adelaide",
      "Canberra"                     => "Australia/Melbourne",
      "Melbourne"                    => "Australia/Melbourne",
      "Sydney"                       => "Australia/Sydney",
      "Brisbane"                     => "Australia/Brisbane",
      "Hobart"                       => "Australia/Hobart",
      "Vladivostok"                  => "Asia/Vladivostok",
      "Guam"                         => "Pacific/Guam",
      "Port Moresby"                 => "Pacific/Port_Moresby",
      "Magadan"                      => "Asia/Magadan",
      "Solomon Is."                  => "Asia/Magadan",
      "New Caledonia"                => "Pacific/Noumea",
      "Fiji"                         => "Pacific/Fiji",
      "Kamchatka"                    => "Asia/Kamchatka",
      "Marshall Is."                 => "Pacific/Majuro",
      "Auckland"                     => "Pacific/Auckland",
      "Wellington"                   => "Pacific/Auckland",
      "Nuku'alofa"                   => "Pacific/Tongatapu"
    }.each { |name, zone| name.freeze; zone.freeze }
    MAPPING.freeze
  end

  include Comparable
  attr_reader :name

  # Create a new TimeZone object with the given name and offset. The
  # offset is the number of seconds that this time zone is offset from UTC
  # (GMT). Seconds were chosen as the offset unit because that is the unit that
  # Ruby uses to represent time zone offsets (see Time#utc_offset).
  def initialize(name, utc_offset, tzinfo = nil)
    @name = name
    @utc_offset = utc_offset
    @tzinfo = tzinfo
  end

  def utc_offset
    @utc_offset ||= tzinfo.current_period.utc_offset
  end

  # Returns the offset of this time zone as a formatted string, of the
  # format "+HH:MM".
  def formatted_offset(colon=true, alternate_utc_string = nil)
    utc_offset == 0 && alternate_utc_string || utc_offset.to_utc_offset_s(colon)
  end

  # Compare this time zone to the parameter. The two are comapred first on
  # their offsets, and then by name.
  def <=>(zone)
    result = (utc_offset <=> zone.utc_offset)
    result = (name <=> zone.name) if result == 0
    result
  end

  # Returns a textual representation of this time zone.
  def to_s
    "(UTC#{formatted_offset}) #{name}"
  end

  # Method for creating new ActiveSupport::TimeWithZone instance in time zone of +self+ from given values. Example:
  #
  #   Time.zone = "Hawaii"                      # => "Hawaii"
  #   Time.zone.local(2007, 2, 1, 15, 30, 45)   # => Thu, 01 Feb 2007 15:30:45 HST -10:00
  def local(*args)
    time = Time.utc_time(*args)
    ActiveSupport::TimeWithZone.new(nil, self, time)
  end

  # Method for creating new ActiveSupport::TimeWithZone instance in time zone of +self+ from number of seconds since the Unix epoch. Example:
  #
  #   Time.zone = "Hawaii"        # => "Hawaii"
  #   Time.utc(2000).to_f         # => 946684800.0
  #   Time.zone.at(946684800.0)   # => Fri, 31 Dec 1999 14:00:00 HST -10:00
  def at(secs)
    utc = Time.at(secs).utc rescue DateTime.civil(1970).since(secs)
    utc.in_time_zone(self)
  end

  # Method for creating new ActiveSupport::TimeWithZone instance in time zone of +self+ from parsed string. Example:
  #
  #   Time.zone = "Hawaii"                      # => "Hawaii"
  #   Time.zone.parse('1999-12-31 14:00:00')    # => Fri, 31 Dec 1999 14:00:00 HST -10:00
  #
  # If upper components are missing from the string, they are supplied from TimeZone#now:
  #
  #   Time.zone.now                 # => Fri, 31 Dec 1999 14:00:00 HST -10:00
  #   Time.zone.parse('22:30:00')   # => Fri, 31 Dec 1999 22:30:00 HST -10:00
  def parse(str, now=now)
    date_parts = Date._parse(str)
    return if date_parts.blank?
    time = Time.parse(str, now) rescue DateTime.parse(str)
    if date_parts[:offset].nil?
      ActiveSupport::TimeWithZone.new(nil, self, time)
    else
      time.in_time_zone(self)
    end
  end

  # Returns an ActiveSupport::TimeWithZone instance representing the current time
  # in the time zone represented by +self+. Example:
  #
  #   Time.zone = 'Hawaii'  # => "Hawaii"
  #   Time.zone.now         # => Wed, 23 Jan 2008 20:24:27 HST -10:00
  def now
    Time.now.utc.in_time_zone(self)
  end

  # Return the current date in this time zone.
  def today
    tzinfo.now.to_date
  end

  # Adjust the given time to the simultaneous time in the time zone represented by +self+. Returns a
  # Time.utc() instance -- if you want an ActiveSupport::TimeWithZone instance, use Time#in_time_zone() instead.
  def utc_to_local(time)
    tzinfo.utc_to_local(time)
  end

  # Adjust the given time to the simultaneous time in UTC. Returns a Time.utc() instance.
  def local_to_utc(time, dst=true)
    tzinfo.local_to_utc(time, dst)
  end

  # Available so that TimeZone instances respond like TZInfo::Timezone instances
  def period_for_utc(time)
    tzinfo.period_for_utc(time)
  end

  # Available so that TimeZone instances respond like TZInfo::Timezone instances
  def period_for_local(time, dst=true)
    tzinfo.period_for_local(time, dst)
  end

  # TODO: Preload instead of lazy load for thread safety
  def tzinfo
    @tzinfo ||= TZInfo::Timezone.get(MAPPING[name])
  end

  unless const_defined?(:ZONES)
    ZONES = []
    ZONES_MAP = {}
    [[-39_600, "International Date Line West", "Midway Island", "Samoa" ],
     [-36_000, "Hawaii" ],
     [-32_400, "Alaska" ],
     [-28_800, "Pacific Time (US & Canada)", "Tijuana" ],
     [-25_200, "Mountain Time (US & Canada)", "Chihuahua", "Mazatlan",
               "Arizona" ],
     [-21_600, "Central Time (US & Canada)", "Saskatchewan", "Guadalajara",
               "Mexico City", "Monterrey", "Central America" ],
     [-18_000, "Eastern Time (US & Canada)", "Indiana (East)", "Bogota",
               "Lima", "Quito" ],
     [-14_400, "Atlantic Time (Canada)", "Caracas", "La Paz", "Santiago" ],
     [-12_600, "Newfoundland" ],
     [-10_800, "Brasilia", "Buenos Aires", "Georgetown", "Greenland" ],
     [ -7_200, "Mid-Atlantic" ],
     [ -3_600, "Azores", "Cape Verde Is." ],
     [      0, "Dublin", "Edinburgh", "Lisbon", "London", "Casablanca",
               "Monrovia", "UTC" ],
     [  3_600, "Belgrade", "Bratislava", "Budapest", "Ljubljana", "Prague",
               "Sarajevo", "Skopje", "Warsaw", "Zagreb", "Brussels",
               "Copenhagen", "Madrid", "Paris", "Amsterdam", "Berlin",
               "Bern", "Rome", "Stockholm", "Vienna",
               "West Central Africa" ],
     [  7_200, "Bucharest", "Cairo", "Helsinki", "Kyev", "Riga", "Sofia",
               "Tallinn", "Vilnius", "Athens", "Istanbul", "Minsk",
               "Jerusalem", "Harare", "Pretoria" ],
     [ 10_800, "Moscow", "St. Petersburg", "Volgograd", "Kuwait", "Riyadh",
               "Nairobi", "Baghdad" ],
     [ 12_600, "Tehran" ],
     [ 14_400, "Abu Dhabi", "Muscat", "Baku", "Tbilisi", "Yerevan" ],
     [ 16_200, "Kabul" ],
     [ 18_000, "Ekaterinburg", "Islamabad", "Karachi", "Tashkent" ],
     [ 19_800, "Chennai", "Kolkata", "Mumbai", "New Delhi" ],
     [ 20_700, "Kathmandu" ],
     [ 21_600, "Astana", "Dhaka", "Sri Jayawardenepura", "Almaty",
               "Novosibirsk" ],
     [ 23_400, "Rangoon" ],
     [ 25_200, "Bangkok", "Hanoi", "Jakarta", "Krasnoyarsk" ],
     [ 28_800, "Beijing", "Chongqing", "Hong Kong", "Urumqi",
               "Kuala Lumpur", "Singapore", "Taipei", "Perth", "Irkutsk",
               "Ulaan Bataar" ],
     [ 32_400, "Seoul", "Osaka", "Sapporo", "Tokyo", "Yakutsk" ],
     [ 34_200, "Darwin", "Adelaide" ],
     [ 36_000, "Canberra", "Melbourne", "Sydney", "Brisbane", "Hobart",
               "Vladivostok", "Guam", "Port Moresby" ],
     [ 39_600, "Magadan", "Solomon Is.", "New Caledonia" ],
     [ 43_200, "Fiji", "Kamchatka", "Marshall Is.", "Auckland",
               "Wellington" ],
     [ 46_800, "Nuku'alofa" ]].
    each do |offset, *places|
      places.each do |place|
        place.freeze
        zone = new(place, offset)
        ZONES << zone
        ZONES_MAP[place] = zone
      end
    end
    ZONES.sort!
    ZONES.freeze
    ZONES_MAP.freeze
  end

  class << self
    alias_method :create, :new

    # Return a TimeZone instance with the given name, or +nil+ if no
    # such TimeZone instance exists. (This exists to support the use of
    # this class with the #composed_of macro.)
    def new(name)
      self[name]
    end

    # Return an array of all TimeZone objects. There are multiple
    # TimeZone objects per time zone, in many cases, to make it easier
    # for users to find their own time zone.
    def all
      ZONES
    end

    # Locate a specific time zone object. If the argument is a string, it
    # is interpreted to mean the name of the timezone to locate. If it is a
    # numeric value it is either the hour offset, or the second offset, of the
    # timezone to find. (The first one with that offset will be returned.)
    # Returns +nil+ if no such time zone is known to the system.
    def [](arg)
      case arg
        when String
          ZONES_MAP[arg]
        when Numeric, ActiveSupport::Duration
          arg *= 3600 if arg.abs <= 13
          all.find { |z| z.utc_offset == arg.to_i }
        else
          raise ArgumentError, "invalid argument to TimeZone[]: #{arg.inspect}"
      end
    end

    # A regular expression that matches the names of all time zones in
    # the USA.
    US_ZONES = /US|Arizona|Indiana|Hawaii|Alaska/.freeze

    # A convenience method for returning a collection of TimeZone objects
    # for time zones in the USA.
    def us_zones
      all.find_all { |z| z.name =~ US_ZONES }
    end
  end
end