icalendar | Library for reading and writing iCalendar files in PHP | Calendar library

• If you don't have an instance of it already in your code, you need to create an instance of RssProdutos as a resource in your xaml by giving it a key:

If I understand the requirement correctly, it is not exactly conditional. It is that ONLY the first of the first Monday and first Wednesday is required. BYSETPOS is aimed at this.

In this example, it is being used to calculate the last working day https://icalevents.com/2555-paydays-last-working-days-and-why-bysetpos-is-useful/

For your example

RRULE:FREQ=MONTHLY;BYDAY=1MO,1WE;BYSETPOS=1

should do the trick,

Basically the RRULE will expand out all the first MONDAY and WEDNESDAYs and then 'contract' ie take the first date of each pair.

Page 43 of the specification https://www.ietf.org/rfc/rfc5545.txt shows the priorities of the 'expansions' and 'contractions'.

Okay, so after a lot of trial and error I finally got this working. I hope the code will be helpful to others.

So, firstly, what I did was send an actual event invite from iCalendar and receive this .ics invite (which actually got rendered in both Outlook and Gmail). I looked at how this file was different from what I was generating and found a curious thing:

the key to get this working was...

MAGIC STRINGS

Yeah, totally random, weird magic strings.

Below I'm posting the .ics file content that worked for me.

TOTTALLY-RANDOM-MAGIC-STRING - is a placeholder for a totally random strings like uuids or maybe your organisation emails or anything else.

The key is: with these strings in the file Outlook and Gmail render the invite correctly, and without them - don't. Weird, but working.

I wasn't able to find anything meaningful about this in the docs or RFCs, so I guess it's safe for now to call these magic strings.

The first magic string is TOTTALLY-RANDOM-MAGIC-STRING@imip.me.com.

And the second magic string is /TOTTALLY-RANDOM-MAGIC-STRING/principal/.

Re: "How to calculate the timezone offset":

It is not 'calculated', but rather looked up - most systems have this information built in using the Olson timezone database, and kept (hopefully) up to date. The systems or languages usually have a function to get the offset for a given date and time. EG:

• in php https://www.php.net/manual/en/datetime.getoffset.php. or one can get all the transitions to output to a VTIMEZONE https://www.php.net/manual/en/datetimezone.gettransitions.php
• general comment here https://en.wikipedia.org/wiki/Time_zone#Computer_systems

Most systems maintain such a db. Usually there is a recurring rule that always is so, however countries and areas may change the date of daylight saving change. See https://en.wikipedia.org/wiki/Daylight_saving_time_in_Australia#Western_Australia and changes made for the Olympics. This would mean an extra set of VTIMEZONE DST transition definitions for those areas, with DTSTARTS and UNTIL's on any recurring rules to indicate over what years they apply or do not apply.

Now the .ics specification says we must include these timezone transitions - the daylight saving changes in a VTIMEZONE definition in the file.

That leads us to your other question:

RE: what is TZOFFSETFROM and TZOFFSETTO?

They are literally for each transition date generated by the RRULE (or just a date if not recurring if it was a one-off), relative to UTC or GMT:

• the OFFSET FROM which a daylight saving change is coming and
• the OFFSET TO which a daylight saving change is going

Take the New York 2021 daylight savings change on 14 March. The timezone offset is -5. After 14 march 2021 2 am, the timezoneoffset will be -4. See https://www.timeanddate.com/time/zone/usa/new-york-state.

So If we look at what google calendar outputs, we see that on the second sunday of march at 2am, Daylight saving begins, NY goes

• FROM -05 and
• TO -04.

Then when they revert to Standard Time on the 1st sunday in November, NY goes

• FROM an offset of -04 and
• TO an offset of -05.

NOTE that both (a FROM and a TO offset) are required because the change is NOT always by an hour. Sometimes the change may be 30 minutes. See https://www.timeanddate.com/time/time-zones-interesting.html and scroll down near the bottom. You'll see Lord Howe Island had a 1/2 hour change and further down under 'Historic half hour offsets' what North Korea did in 2015 and Venezuela in 2016.

Google Calendar New York example:

Ok - After many hours of reading RFC5546, Stackoverflow, and many other blogs, I finally have the answers.

Scope:

1. Sending calendar invites to Gmail / Outlook / Privateemail (namecheap's email client)
2. Email clients automatically recognizing .ics files and generating "accept" templates
3. Events automatically appearing in client calendars as "tentative"
4. Sending event revisions that automatically move client calendar events

There are two fundamental principles that are critical to making this work:

1. The contents of the .ics file must very closely match the .ics file of the Gmail / Outlook community, this includes the parameters and the order of the parameters.

2. The way the .ics file is attached to the email transmission is odd but critical: (a) the .ics file must be turned into 'base64', and (b) the headers of the file need to give a type: 'text/calendar;method=REQUEST;name="file.ics"'

Below I will give examples of each, which I hope save others time on this process.

.ics Content Example:

Try this:

Turns out that everything is working as expected, but – just as @anmari pointed out in a comment – receiving applications check at their own pace.

Most likely what is happening is that you are trying this code on a read item. The getAttachmentsAsync fn only exists in compose mode, so you would see the error above if you are not composing an email. For read emails you should be able to just access the attachments property Office.context.mailbox.item.attachments (https://docs.microsoft.com/en-us/javascript/api/outlook/office.attachmentdetails?view=outlook-js-preview)