Multiple times VTIMEZONE set doesn't work

[arwinvdv]

• PHP Version: 7.2.21
• ICS Parser Version: 2.1.15

Description of the Issue:

I have a ical from Microsoft and Google with 2 VTIMEZONE's defined. The parser only uses 1 timezone.

Steps to Reproduce:

1. Use this ical from Microsoft:

   BEGIN:VCALENDAR
   METHOD:PUBLISH
   PRODID:Microsoft Exchange Server 2010
   VERSION:2.0
   X-WR-CALNAME:Example calendar
   BEGIN:VTIMEZONE
   TZID:Customized Time Zone
   BEGIN:STANDARD
   DTSTART:16010101T030000
   TZOFFSETFROM:+0200
   TZOFFSETTO:+0100
   RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=10
   END:STANDARD
   BEGIN:DAYLIGHT
   DTSTART:16010101T020000
   TZOFFSETFROM:+0100
   TZOFFSETTO:+0200
   RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=3
   END:DAYLIGHT
   END:VTIMEZONE
   BEGIN:VTIMEZONE
   TZID:Greenwich Standard Time
   BEGIN:STANDARD
   DTSTART:16010101T000000
   TZOFFSETFROM:+0000
   TZOFFSETTO:+0000
   END:STANDARD
   BEGIN:DAYLIGHT
   DTSTART:16010101T000000
   TZOFFSETFROM:+0000
   TZOFFSETTO:+0000
   END:DAYLIGHT
   END:VTIMEZONE
   BEGIN:VEVENT
   UID:0123
   SUMMARY:example consult 1
   DTSTART;TZID=Customized Time Zone:20191003T093000
   DTEND;TZID=Customized Time Zone:20191003T110000
   CLASS:PUBLIC
   PRIORITY:5
   DTSTAMP:20200103T132704Z
   TRANSP:OPAQUE
   STATUS:CONFIRMED
   SEQUENCE:0
   LOCATION:
   X-MICROSOFT-CDO-APPT-SEQUENCE:0
   X-MICROSOFT-CDO-BUSYSTATUS:BUSY
   X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY
   X-MICROSOFT-CDO-ALLDAYEVENT:FALSE
   X-MICROSOFT-CDO-IMPORTANCE:1
   X-MICROSOFT-CDO-INSTTYPE:0
   X-MICROSOFT-DONOTFORWARDMEETING:FALSE
   X-MICROSOFT-DISALLOW-COUNTER:FALSE
   END:VEVENT
   BEGIN:VEVENT
   UID:12345
   SUMMARY:example consult 2
   DTSTART;TZID=Greenwich Standard Time:20191003T093000
   DTEND;TZID=Greenwich Standard Time:20191003T110000
   CLASS:PUBLIC
   PRIORITY:5
   DTSTAMP:20200103T132704Z
   TRANSP:OPAQUE
   STATUS:CONFIRMED
   SEQUENCE:0
   LOCATION:
   X-MICROSOFT-CDO-APPT-SEQUENCE:0
   X-MICROSOFT-CDO-BUSYSTATUS:BUSY
   X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY
   X-MICROSOFT-CDO-ALLDAYEVENT:FALSE
   X-MICROSOFT-CDO-IMPORTANCE:1
   X-MICROSOFT-CDO-INSTTYPE:0
   X-MICROSOFT-DONOTFORWARDMEETING:FALSE
   X-MICROSOFT-DISALLOW-COUNTER:FALSE
   END:VEVENT
   END:VCALENDAR

2. The parser doesn't handle the 2 timezones. The 2 events has the same time as output, but they have a different timezone.

[u01jmg3]

@s0600204: I understand if you're busy but your input would be welcome on this issue

[s0600204]

The primary issue here can be summed up as a quote from the project's readme:

Requirements

• PHP 5 (≥ 5.6)
• Valid ICS (.ics, .ical, .ifb) file
• IANA, Unicode CLDR or Windows Time Zones

The timezone named Customized Time Zone fails the third requirement.

---

In order to support user-defined timezones, we'd need a way to specify a timezone in a way that PHP's DateTime class can understand/use it. In other words: we'd need to take what's defined in a VTIMEZONE block and convert it into a DateTimeZone class instance.

Unfortunately, DateTimeZone itself lacks full support for user-defined timezones (with daylight savings transitions et al.) - the best it can do is a single offset-from-UTC.

Thus to support a Standard/Daylight transition we'd need to create two DateTimeZone instances - one for "Standard" and one for "Daylight [Savings]". We'd also need a way to detect which of these two are in effect for any given date-time; apply them consistently with regards to event recurrences; and only do this if the timezone is a user-defined one.

[u01jmg3]

@arwinvdv: in light of the info @s0600204 has kindly provided, at this point in time, I won't be exploring user-defined timezones unless more users are interested in such a feature. However, if you want to put a PR together, I'd be happy to take a look.