feat: support adding and fetching recurrence with rrule

[differental]

Adds support of adding and fetching recurrence with rrule, which follows RFC-5545. Tests are added as well.

Note: Presumably src/period.rs and src/repeats.rs can be removed if this is a satisfactory implementation.

[qwandor]

It looks like this ignores any EXRULE, RDATE or EXDATE from the set, which seems misleading. I think it should either add them as well (and maybe do something about the DTSTART matching?) or take an RRule rather than an RRuleSet.

[differental]

RDATE and EXDATE added - thanks for spotting this. (EXRULE is deprecated)

For DTSTART matching, I can try adding it. The logic might become a bit complex though, since rrule takes a chrono::DateTime<Tz> and icalendar has a DatePerhapsTime. I would imagine it'll need some methods under chrono-tz flag, so I'm not sure whether it's best to be included in this pr as well... open to your thoughts. ;)

[differental]

Sorry for the oversight. rrule v0.10.0 is the latest supported by rustc 1.60, hence that was added when I ran cargo add.

v0.10.0 also did not put RDATE, EXRULE and EXDATE in fmt, leading me to believe everything's in RRULE.

I'll update my pr to include these three, hopefully v0.10.0 is sufficient.

[hoodie]

Hi, first of all thanks for the contribution. I've been putting this off thinking we could maybe implement a native/own version of this here at some point, but now that I've looked at the rrule crate, there's a lot of stuff in there that I wouldn't want to debug myself 😆

I welcome this addition, still, it pulls in a large dependency and change a few things. So let's be a bit careful. I would recommend making this an optional feature and making sure that it works together well with the parsing aspects of this library.

[hoodie]

You probably have some nice usecase for rrule. Could you perhaps write one or two examples that illustrate what we can do with it?

[hoodie]

I was just playing with it briefly, I don't have a lot of time so I didn't get a good feel for the api yet. It might be that the API experience is still a bit complicated, when you have to give it a start data with the rrule tz. Also I wonder if an event itself that has a recurrence should maybe implement ToIterator or something?

Here is my short attempt at an example (5min efford).

use chrono::*;
use icalendar::*;

fn main() {
    let my_calendar = Calendar::new()
        .name("example calendar")
        .push(
            // add an all-day event
            Event::new()
                .all_day(NaiveDate::from_ymd_opt(2016, 3, 15).unwrap())
                .recurrence(
                    rrule::RRule::new(rrule::Frequency::Yearly)
                        .build(chrono::Utc::now().with_timezone(&rrule::Tz::UTC))
                        .unwrap(),
                )
                .summary("My Birthday")
                .description("Hey, I'm gonna have a party\nBYOB: Bring your own beer.\nHendrik")
                .done(),
        )
        .done();

    for event in my_calendar
        .components
        .first()
        .unwrap()
        .as_event()
        .unwrap()
        .get_recurrence()
        .iter()
    {
        println!("Event: {:?}", event);
    }

[hoodie]

Would be nice if we could create a birthday event and then .iter().take(5) print the first 5 occurences of the event. or similar. I'm not saying you have to write this example, I'm just dumping my brain :D

[differental]

The recurrence_parse example isn't working as intended - the example ics in fixtures/icalendar-rb/recurrence.ics seems to not have EXDATE immediately after RRULE and this is causing issues. I'll change the code to parse them separately

[differental]

Oops sorry didn't see the comments - I added two examples that seem to work, and thankfully the parsing example with the recurrence fixture helped me discover the bug with parsing ics. Had to make some significant changes but now everything should work - I added an extra test just to be sure

[differental]

Would be nice if we could create a birthday event and then .iter().take(5) print the first 5 occurences of the event. or similar. I'm not saying you have to write this example, I'm just dumping my brain :D

That actually looks cleaner than their "recommended" method .all(limit).dates -> Vec<DateTime>, maybe I should change the one I added to the example ;)

Sorry for messing this up by the way, I'm glad there were some fixture ics that caught my bug

[hoodie]

No worries. Still grateful for the contribution. This is actually a complex feature. Let's take it slow.

[differental]

It should work now though, I'll double-check the parsing just in case