feat: add timezone parsing support with tests from @epologee

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Added
 - Indonesian translations. ([#505](https://github.com/seejohnrun/ice_cube/pull/505)) by [@achmiral](https://github.com/achmiral)
+- The `IceCube::IcalParser` finds the time zones matching an iCal schedule's date/time strings, accomodating for times with daylight savings ([#555](https://github.com/ice-cube-ruby/ice_cube/pull/555)) by [@jankeesvw](https://github.com/jankeesvw) and [@epologee](https://github.com/epologee)
 
 ### Changed
 - Removed use of `delegate` method added in [66f1d797](https://github.com/ice-cube-ruby/ice_cube/commit/66f1d797092734563bfabd2132c024c7d087f683) , reverting to previous implementation. ([#522](https://github.com/ice-cube-ruby/ice_cube/pull/522))  by [@pacso](https://github.com/pacso)

lib/ice_cube/parsers/ical_parser.rb

@@ -4,18 +4,27 @@ def self.schedule_from_ical(ical_string, options = {})
       data = {}
       ical_string.each_line do |line|
         (property, value) = line.split(":")
-        (property, _tzid) = property.split(";")
+        (property, tzid) = property.split(";")
+        zone = find_zone(tzid, value) if tzid
         case property
         when "DTSTART"
+          value = { time: value, zone: zone } if zone
           data[:start_time] = TimeUtil.deserialize_time(value)
         when "DTEND"
+          value = { time: value, zone: zone } if zone
           data[:end_time] = TimeUtil.deserialize_time(value)
         when "RDATE"
           data[:rtimes] ||= []
-          data[:rtimes] += value.split(",").map { |v| TimeUtil.deserialize_time(v) }
+          data[:rtimes] += value.split(",").map do |v|
+            v = {time: v, zone: zone} if zone
+            TimeUtil.deserialize_time(v)
+          end
         when "EXDATE"
           data[:extimes] ||= []
-          data[:extimes] += value.split(",").map { |v| TimeUtil.deserialize_time(v) }
+          data[:extimes] += value.split(",").map do |v|
+            v = {time: v, zone: zone} if zone
+            TimeUtil.deserialize_time(v)
+          end
         when "DURATION"
           data[:duration] # FIXME
         when "RRULE"
@@ -83,5 +92,20 @@ def self.rule_from_ical(ical)
 
       Rule.from_hash(params)
     end
+
+    private_class_method def self.find_zone(tzid, time_string)
+      (_, zone) = tzid&.split("=")
+      begin
+        Time.find_zone!(zone) if zone
+      rescue ArgumentError
+        (rails_zone, _tzinfo_id) = ActiveSupport::TimeZone::MAPPING.find do |(k, _)|
+          time = Time.parse(time_string)
+
+          Time.find_zone!(k).local(time.year, time.month, time.day, time.hour, time.min).strftime("%Z") == zone
+        end
+
+        Time.find_zone(rails_zone)
+      end
+    end
   end
 end

spec/examples/from_ical_spec.rb

@@ -348,6 +348,69 @@ def sorted_ical(ical)
       end
     end
 
+    describe "time zone support" do
+      it "parses start time with the correct time zone" do
+        schedule = IceCube::Schedule.from_ical ical_string_with_multiple_rules
+
+        expect(schedule.start_time).to eq Time.find_zone!("America/Chicago").local(2015, 10, 5, 19, 55, 41)
+      end
+
+      it "parses time zones correctly" do
+        schedule = IceCube::Schedule.from_ical ical_string_with_multiple_exdates_and_rdates
+
+        utc_times = [
+          schedule.recurrence_rules.map(&:until_time)
+        ].flatten
+
+        denver_times = [
+          schedule.start_time,
+          schedule.end_time,
+          schedule.exception_times,
+          schedule.rtimes
+        ].flatten
+
+        utc_times.each do |t|
+          expect(t.zone).to eq "UTC"
+        end
+
+        denver_times.each do |t|
+          expect(t.zone).to eq "MDT"
+        end
+      end
+
+      it "round trips from and to ical with time zones in the summer (MDT)" do
+        original = <<-ICAL.gsub(/^\s*/, "").strip
+          DTSTART;TZID=MDT:20130731T143000
+          RRULE:FREQ=WEEKLY;UNTIL=20140730T203000Z;BYDAY=MO,WE,FR
+          RDATE;TZID=MDT:20150812T143000
+          RDATE;TZID=MDT:20150807T143000
+          EXDATE;TZID=MDT:20130823T143000
+          EXDATE;TZID=MDT:20130812T143000
+          EXDATE;TZID=MDT:20130807T143000
+          DTEND;TZID=MDT:20130731T153000
+        ICAL
+
+        schedule_from_ical = IceCube::Schedule.from_ical original
+        expect(schedule_from_ical.to_ical).to eq original
+      end
+
+      it "round trips from and to ical with time zones in the winter (MST)" do
+        original = <<-ICAL.gsub(/^\s*/, "").strip
+          DTSTART;TZID=MST:20130131T143000
+          RRULE:FREQ=WEEKLY;UNTIL=20140130T203000Z;BYDAY=MO,WE,FR
+          RDATE;TZID=MST:20150212T143000
+          RDATE;TZID=MST:20150207T143000
+          EXDATE;TZID=MST:20130223T143000
+          EXDATE;TZID=MST:20130212T143000
+          EXDATE;TZID=MST:20130207T143000
+          DTEND;TZID=MST:20130131T153000
+        ICAL
+
+        schedule_from_ical = IceCube::Schedule.from_ical original
+        expect(schedule_from_ical.to_ical).to eq original
+      end
+    end
+
     describe "exceptions" do
       it "handles single EXDATE lines, single RDATE lines" do
         start_time = Time.now