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require 'active_support/core_ext/object/blank'
require 'active_support/core_ext/object/try'

module ActiveSupport
  # The TimeZone class serves as a wrapper around TZInfo::Timezone instances.
  # It allows us to do the following:
  #
  # * Limit the set of zones provided by TZInfo to a meaningful subset of 146
  # zones.
  # * Retrieve and display zones with a friendlier name
  # (e.g., "Eastern Time (US & Canada)" instead of "America/New_York").
  # * Lazily load TZInfo::Timezone instances only when they're needed.
  # * Create ActiveSupport::TimeWithZone instances via TimeZone's +local+,
  # +parse+, +at+ and +now+ methods.
  #
  # If you set <tt>config.time_zone</tt> in the Rails Application, you can
  # access this TimeZone object via <tt>Time.zone</tt>:
  #
  # # application.rb:
  # class Application < Rails::Application
  # config.time_zone = 'Eastern Time (US & Canada)'
  # end
  #
  # Time.zone # => #<TimeZone:0x514834...>
  # Time.zone.name # => "Eastern Time (US & Canada)"
  # Time.zone.now # => Sun, 18 May 2008 14:30:44 EDT -04:00
  #
  # The version of TZInfo bundled with Active Support only includes the
  # definitions necessary to support the zones defined by the TimeZone class.
  # If you need to use zones that aren't defined by TimeZone, you'll need to
  # install the TZInfo gem (if a recent version of the gem is installed locally,
  # this will be used instead of the bundled version.)
  class TimeZone
    # Keys are Rails TimeZone names, values are TZInfo identifiers.
    MAPPING = {
      "International Date Line West" => "Pacific/Midway",
      "Midway Island" => "Pacific/Midway",
      "American 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/Sao_Paulo",
      "Buenos Aires" => "America/Argentina/Buenos_Aires",
      "Montevideo" => "America/Montevideo",
      "Georgetown" => "America/Guyana",
      "Greenland" => "America/Godthab",
      "Mid-Atlantic" => "Atlantic/South_Georgia",
      "Azores" => "Atlantic/Azores",
      "Cape Verde Is." => "Atlantic/Cape_Verde",
      "Dublin" => "Europe/Dublin",
      "Edinburgh" => "Europe/London",
      "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",
      "Kyiv" => "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/Kathmandu",
      "Astana" => "Asia/Dhaka",
      "Dhaka" => "Asia/Dhaka",
      "Sri Jayawardenepura" => "Asia/Colombo",
      "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",
      "Ulaanbaatar" => "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." => "Pacific/Guadalcanal",
      "New Caledonia" => "Pacific/Noumea",
      "Fiji" => "Pacific/Fiji",
      "Kamchatka" => "Asia/Kamchatka",
      "Marshall Is." => "Pacific/Majuro",
      "Auckland" => "Pacific/Auckland",
      "Wellington" => "Pacific/Auckland",
      "Nuku'alofa" => "Pacific/Tongatapu",
      "Tokelau Is." => "Pacific/Fakaofo",
      "Chatham Is." => "Pacific/Chatham",
      "Samoa" => "Pacific/Apia"
    }

    UTC_OFFSET_WITH_COLON = '%s%02d:%02d'
    UTC_OFFSET_WITHOUT_COLON = UTC_OFFSET_WITH_COLON.sub(':', '')

    # Assumes self represents an offset from UTC in seconds (as returned from
    # Time#utc_offset) and turns this into an +HH:MM formatted string.
    #
    # TimeZone.seconds_to_utc_offset(-21_600) # => "-06:00"
    def self.seconds_to_utc_offset(seconds, colon = true)
      format = colon ? UTC_OFFSET_WITH_COLON : UTC_OFFSET_WITHOUT_COLON
      sign = (seconds < 0 ? '-' : '+')
      hours = seconds.abs / 3600
      minutes = (seconds.abs % 3600) / 60
      format % [sign, hours, minutes]
    end

    include Comparable
    attr_reader :name
    attr_reader :tzinfo

    # 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 = nil, tzinfo = nil)
      self.class.send(:require_tzinfo)

      @name = name
      @utc_offset = utc_offset
      @tzinfo = tzinfo || TimeZone.find_tzinfo(name)
      @current_period = nil
    end

    # Returns the offset of this time zone from UTC in seconds.
    def utc_offset
      if @utc_offset
        @utc_offset
      else
        @current_period ||= tzinfo.try(:current_period)
        @current_period.try(:utc_offset)
      end
    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 || self.class.seconds_to_utc_offset(utc_offset, colon)
    end

    # Compare this time zone to the parameter. The two are compared 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

    # Compare #name and TZInfo identifier to a supplied regexp, returning +true+
    # if a match is found.
    def =~(re)
      re === name || re === MAPPING[name]
    end

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

    # Method for creating new ActiveSupport::TimeWithZone instance in time zone
    # of +self+ from given values.
    #
    # 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(*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.
    #
    # 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)
      Time.at(secs).utc.in_time_zone(self)
    end

    # Method for creating new ActiveSupport::TimeWithZone instance in time zone
    # of +self+ from parsed string.
    #
    # 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)
      parts = Date._parse(str, false)
      return if parts.empty?

      time = Time.new(
        parts.fetch(:year, now.year),
        parts.fetch(:mon, now.month),
        parts.fetch(:mday, now.day),
        parts.fetch(:hour, 0),
        parts.fetch(:min, 0),
        parts.fetch(:sec, 0) + parts.fetch(:sec_fraction, 0),
        parts.fetch(:offset, 0)
      )

      if parts[:offset]
        TimeWithZone.new(time.utc, self)
      else
        TimeWithZone.new(nil, self, time)
      end
    end

    # Returns an ActiveSupport::TimeWithZone instance representing the current
    # time in the time zone represented by +self+.
    #
    # 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

    def self.find_tzinfo(name)
      TZInfo::TimezoneProxy.new(MAPPING[name] || name)
    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 ||= zones_map.values.sort
      end

      def zones_map
        @zones_map ||= begin
          new_zones_names = MAPPING.keys - lazy_zones_map.keys
          new_zones = Hash[new_zones_names.map { |place| [place, create(place)] }]

          lazy_zones_map.merge(new_zones)
        end
      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
          begin
            lazy_zones_map[arg] ||= lookup(arg).tap { |tz| tz.utc_offset }
          rescue TZInfo::InvalidTimezoneIdentifier
            nil
          end
          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 convenience method for returning a collection of TimeZone objects
      # for time zones in the USA.
      def us_zones
        @us_zones ||= all.find_all { |z| z.name =~ /US|Arizona|Indiana|Hawaii|Alaska/ }
      end

      protected

        def require_tzinfo
          require 'tzinfo' unless defined?(::TZInfo)
        rescue LoadError
          $stderr.puts "You don't have tzinfo installed in your application. Please add it to your Gemfile and run bundle install"
          raise
        end

      private

        def lookup(name)
          (tzinfo = find_tzinfo(name)) && create(tzinfo.name.freeze)
        end

        def lazy_zones_map
          require_tzinfo

          @lazy_zones_map ||= Hash.new do |hash, place|
            hash[place] = create(place) if MAPPING.has_key?(place)
          end
        end
    end

    private

    def time_now
      Time.now
    end
  end
end
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