Parse ISO-8601 time strings and respect the embedded time zone.

time_utilities.rb

require 'active_support/core_ext/time'
require 'active_support/values/time_zone'

module TimeUtilities

  # Parses an ISO-8601 time string with a time zone and keeps the time zone in
  # the Time object returned, unlike Ruby Core.
  #
  # Examples:
  #
  # >> s = TimeUtilities.parse_with_time_zone('2014-08-15T15:35:00Z').utc_offset
  # => 0
  #
  # >> s = TimeUtilities.parse_with_time_zone('2014-08-15T15:35:00-05:00').utc_offset
  # => -18000
  # >> ActiveSupport::TimeZone.seconds_to_utc_offset(s)
  # => "-05:00"
  #
  # @param time_string [String] an ISO-8601 time string with a time zone
  # @return [ActiveSupport::TimeWithZone]
  #
  def self.parse_with_time_zone(time_string)
    unless time_string[4] == '-' && time_string[10] == 'T' && '-+Z'.include?(time_string[19])
      raise ArgumentError, "Must be an ISO-8601-formatted date."
    end

    if time_string[-1] == 'Z'
      ActiveSupport::TimeZone['UTC'].parse(time_string)
    else # -05:00 / +09:30 / +11:00
      offset  = time_string[-6..-1]
      sign    = offset[0] == '-' ? -1 : 1
      hours   = offset[1] == '0' ? Integer(offset[2]) : Integer(offset[1..2])
      minutes = offset[4] == '0' ? Integer(offset[5]) : Integer(offset[4..5])

      offset_seconds = ((hours * 60 * 60) + (minutes * 60)) * sign
      zone = ActiveSupport::TimeZone[offset_seconds]
      raise "Unknown time zone with offset: #{ActiveSupport::TimeZone.seconds_to_utc_offset(offset_seconds)}" unless zone
      zone.parse(time_string[0...-6])
    end
  end

end

time_utilities_spec.rb

require_relative '../spec_helper'

describe TimeUtilities do
  describe '.parse_with_time_zone' do
    let(:m) { described_class.method(:parse_with_time_zone) }

    context "for a time in UTC" do
      it "gives back a Time object that has its time zone as UTC" do
        expect(m['2014-08-15T13:55:00Z'].utc?).to be_true
      end
    end

    context "for a time in a negative offset time zone" do
      it "gives back a Time object that has its time zone set correctly" do
        time = m['2014-08-15T13:55:00-05:00']
        expect(ActiveSupport::TimeZone.seconds_to_utc_offset(time.utc_offset)).to eq('-05:00')
      end
    end

    context "for a time in a positive offset time zone" do
      it "gives back a Time object that has its time zone set correctly" do
        time = m['2014-08-15T13:55:00+11:00']
        expect(ActiveSupport::TimeZone.seconds_to_utc_offset(time.utc_offset)).to eq('+11:00')
      end
    end

    context "for a time in an invalid time zone" do
      it "raises an exception" do
        expect { m['2014-08-15T13:55:00-03:27'] }.to raise_exception
      end
    end

    context "for a non-ISO-8601 time string" do
      it "raises an exception" do
        expect { m['2014-08-18 15:49:40 -0400'] }.to raise_exception
      end
    end
  end
end

z-LICENSE

The MIT License

Copyright (c) 2014 Brad Fults, The Last Guide Company

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
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copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
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