Using PHP, turn an array of iCalendar Recurrence Rule properties into an array of event sequences.
This project is new. Structural & architectural changes may occur without warning.
This disclaimer will be removed when stability has been achieved and 1.0 has been tagged.
iCalendar is a widely popular specification that standardizes what an “Event” is and provides directives on how software should expect to interact with them.
It is what Outlook/Office, and Apple Calendar, and Google and others all use for their calendar applications. It’s also what many WordPress Events plugins use, in one way or another, to allow for visitors to subscribe to a feed of events directly from their sites.
From: https://datatracker.ietf.org/doc/html/rfc5545#section-3.8.5.3
This property defines a rule or repeating pattern for recurring events, to-dos, journal entries, or time zone definitions.
It is a single part of the iCalendar specification that is responsible for defining how a single event entry should reoccur multiple times into the future.
This PHP class is a generic way, without any dependencies, to parse an iCalendar RRULE property into an array of event sequences.
It accepts all notations of RFC5545 and its amendments (with basic error correction), looping through them to generate a sequence of events.
It has built-in support for WordPress, but (currently) does not consider it a requirement.
We built this for recurring events in [https://sugarcalendar.com Sugar Calendar], to be able to reliably support every possible recurring event pattern.
We did a bunch of research looking for anything like this already that we could use. We found inspiration in a few places, but nothing quite as simple or effective as we were able to achieve here.
In a WordPress plugin, you can test this quickly with something like...
add_action( 'init', function() {
/**
* First, the "INTERVAL=2" would be applied to "FREQ=YEARLY" to
* arrive at "every other year". Then, "BYMONTH=1" would be applied
* to arrive at "every January, every other year". Then, "BYDAY=SU"
* would be applied to arrive at "every Sunday in January, every
* other year". Then, "BYHOUR=8,9" would be applied to arrive at
* "every Sunday in January at 8 AM and 9 AM, every other year".
* Then, "BYMINUTE=30" would be applied to arrive at "every Sunday in
* January at 8:30 AM and 9:30 AM, every other year". Then, lacking
* information from "RRULE", the second is derived from "DTSTART", to
* end up in "every Sunday in January at 8:30:00 AM and 9:30:00 AM,
* every other year". Similarly, if the BYMINUTE, BYHOUR, BYDAY,
* BYMONTHDAY, or BYMONTH rule part were missing, the appropriate
* minute, hour, day, or month would have been retrieved from the
* "DTSTART" property.
*/
$rule = array(
'dtstart' => '2021-01-03 08:30:00',
'dtend' => '2021-01-03 09:30:00',
'format' => 'Y:m:d H:i:s',
'freq' => 'yearly',
'interval' => '2',
'until' => '2030-01-01 00:00:00',
'bymonth' => '1',
'byday' => 'SU',
'byhour' => '8,9',
'byminute' => '30'
);
// Default return value
$retval = array();
// Load it
$recur = new \Sugar_Calendar\Utilities\iCalendar\Recur\Sequence( $rule );
// Clone Events into sequences
while ( $date = $recur->next() ) {
// Add to return value
$retval[] = $date;
}
// Dump the results
var_dump( $retval ); die;
} );The output looks something like...
array (size=46)
0 =>
array (size=3)
'dtstart' => string '2021-01-03 08:30:00' (length=19)
'dtend' => string '2021-01-03 09:30:00' (length=19)
'recurrence-id' => string '20210103T083000Z' (length=16)
1 =>
array (size=4)
'dtstart' => string '2021-01-03 09:30:00' (length=19)
'dtend' => string '2021-01-03 10:30:00' (length=19)
'recurrence-id' => string '20210103T093000Z' (length=16)
'sequence' => int 1
2 =>
array (size=4)
'dtstart' => string '2021-01-10 08:30:00' (length=19)
'dtend' => string '2021-01-10 09:30:00' (length=19)
'recurrence-id' => string '20210110T083000Z' (length=16)
'sequence' => int 2
3 =>
array (size=4)
'dtstart' => string '2021-01-10 09:30:00' (length=19)
'dtend' => string '2021-01-10 10:30:00' (length=19)
'recurrence-id' => string '20210110T093000Z' (length=16)
'sequence' => int 3
4 =>
array (size=4)
'dtstart' => string '2021-01-17 08:30:00' (length=19)
'dtend' => string '2021-01-17 09:30:00' (length=19)
'recurrence-id' => string '20210117T083000Z' (length=16)
'sequence' => int 4
5 =>
array (size=4)
'dtstart' => string '2021-01-17 09:30:00' (length=19)
'dtend' => string '2021-01-17 10:30:00' (length=19)
'recurrence-id' => string '20210117T093000Z' (length=16)
'sequence' => int 5
6 =>
array (size=4)
'dtstart' => string '2021-01-24 08:30:00' (length=19)
'dtend' => string '2021-01-24 09:30:00' (length=19)
'recurrence-id' => string '20210124T083000Z' (length=16)
'sequence' => int 6
7 =>
array (size=4)
'dtstart' => string '2021-01-24 09:30:00' (length=19)
'dtend' => string '2021-01-24 10:30:00' (length=19)
'recurrence-id' => string '20210124T093000Z' (length=16)
'sequence' => int 7
8 =>
array (size=4)
'dtstart' => string '2021-01-31 08:30:00' (length=19)
'dtend' => string '2021-01-31 09:30:00' (length=19)
'recurrence-id' => string '20210131T083000Z' (length=16)
'sequence' => int 8
9 =>
array (size=4)
'dtstart' => string '2021-01-31 09:30:00' (length=19)
'dtend' => string '2021-01-31 10:30:00' (length=19)
'recurrence-id' => string '20210131T093000Z' (length=16)
'sequence' => int 9
10 =>
array (size=4)
'dtstart' => string '2023-01-01 08:30:00' (length=19)
'dtend' => string '2023-01-01 09:30:00' (length=19)
'recurrence-id' => string '20230101T083000Z' (length=16)
'sequence' => int 10
11 =>
array (size=4)
'dtstart' => string '2023-01-01 09:30:00' (length=19)
'dtend' => string '2023-01-01 10:30:00' (length=19)
'recurrence-id' => string '20230101T093000Z' (length=16)
'sequence' => int 11
12 =>
array (size=4)
'dtstart' => string '2023-01-08 08:30:00' (length=19)
'dtend' => string '2023-01-08 09:30:00' (length=19)
'recurrence-id' => string '20230108T083000Z' (length=16)
'sequence' => int 12
13 =>
array (size=4)
'dtstart' => string '2023-01-08 09:30:00' (length=19)
'dtend' => string '2023-01-08 10:30:00' (length=19)
'recurrence-id' => string '20230108T093000Z' (length=16)
'sequence' => int 13
14 =>
array (size=4)
'dtstart' => string '2023-01-15 08:30:00' (length=19)
'dtend' => string '2023-01-15 09:30:00' (length=19)
'recurrence-id' => string '20230115T083000Z' (length=16)
'sequence' => int 14
15 =>
array (size=4)
'dtstart' => string '2023-01-15 09:30:00' (length=19)
'dtend' => string '2023-01-15 10:30:00' (length=19)
'recurrence-id' => string '20230115T093000Z' (length=16)
'sequence' => int 15
16 =>
array (size=4)
'dtstart' => string '2023-01-22 08:30:00' (length=19)
'dtend' => string '2023-01-22 09:30:00' (length=19)
'recurrence-id' => string '20230122T083000Z' (length=16)
'sequence' => int 16
17 =>
array (size=4)
'dtstart' => string '2023-01-22 09:30:00' (length=19)
'dtend' => string '2023-01-22 10:30:00' (length=19)
'recurrence-id' => string '20230122T093000Z' (length=16)
'sequence' => int 17
18 =>
array (size=4)
'dtstart' => string '2023-01-29 08:30:00' (length=19)
'dtend' => string '2023-01-29 09:30:00' (length=19)
'recurrence-id' => string '20230129T083000Z' (length=16)
'sequence' => int 18
19 =>
array (size=4)
'dtstart' => string '2023-01-29 09:30:00' (length=19)
'dtend' => string '2023-01-29 10:30:00' (length=19)
'recurrence-id' => string '20230129T093000Z' (length=16)
'sequence' => int 19
20 =>
array (size=4)
'dtstart' => string '2025-01-05 08:30:00' (length=19)
'dtend' => string '2025-01-05 09:30:00' (length=19)
'recurrence-id' => string '20250105T083000Z' (length=16)
'sequence' => int 20
21 =>
array (size=4)
'dtstart' => string '2025-01-05 09:30:00' (length=19)
'dtend' => string '2025-01-05 10:30:00' (length=19)
'recurrence-id' => string '20250105T093000Z' (length=16)
'sequence' => int 21
22 =>
array (size=4)
'dtstart' => string '2025-01-12 08:30:00' (length=19)
'dtend' => string '2025-01-12 09:30:00' (length=19)
'recurrence-id' => string '20250112T083000Z' (length=16)
'sequence' => int 22
23 =>
array (size=4)
'dtstart' => string '2025-01-12 09:30:00' (length=19)
'dtend' => string '2025-01-12 10:30:00' (length=19)
'recurrence-id' => string '20250112T093000Z' (length=16)
'sequence' => int 23
24 =>
array (size=4)
'dtstart' => string '2025-01-19 08:30:00' (length=19)
'dtend' => string '2025-01-19 09:30:00' (length=19)
'recurrence-id' => string '20250119T083000Z' (length=16)
'sequence' => int 24
25 =>
array (size=4)
'dtstart' => string '2025-01-19 09:30:00' (length=19)
'dtend' => string '2025-01-19 10:30:00' (length=19)
'recurrence-id' => string '20250119T093000Z' (length=16)
'sequence' => int 25
26 =>
array (size=4)
'dtstart' => string '2025-01-26 08:30:00' (length=19)
'dtend' => string '2025-01-26 09:30:00' (length=19)
'recurrence-id' => string '20250126T083000Z' (length=16)
'sequence' => int 26
27 =>
array (size=4)
'dtstart' => string '2025-01-26 09:30:00' (length=19)
'dtend' => string '2025-01-26 10:30:00' (length=19)
'recurrence-id' => string '20250126T093000Z' (length=16)
'sequence' => int 27
28 =>
array (size=4)
'dtstart' => string '2027-01-03 08:30:00' (length=19)
'dtend' => string '2027-01-03 09:30:00' (length=19)
'recurrence-id' => string '20270103T083000Z' (length=16)
'sequence' => int 28
29 =>
array (size=4)
'dtstart' => string '2027-01-03 09:30:00' (length=19)
'dtend' => string '2027-01-03 10:30:00' (length=19)
'recurrence-id' => string '20270103T093000Z' (length=16)
'sequence' => int 29
30 =>
array (size=4)
'dtstart' => string '2027-01-10 08:30:00' (length=19)
'dtend' => string '2027-01-10 09:30:00' (length=19)
'recurrence-id' => string '20270110T083000Z' (length=16)
'sequence' => int 30
31 =>
array (size=4)
'dtstart' => string '2027-01-10 09:30:00' (length=19)
'dtend' => string '2027-01-10 10:30:00' (length=19)
'recurrence-id' => string '20270110T093000Z' (length=16)
'sequence' => int 31
32 =>
array (size=4)
'dtstart' => string '2027-01-17 08:30:00' (length=19)
'dtend' => string '2027-01-17 09:30:00' (length=19)
'recurrence-id' => string '20270117T083000Z' (length=16)
'sequence' => int 32
33 =>
array (size=4)
'dtstart' => string '2027-01-17 09:30:00' (length=19)
'dtend' => string '2027-01-17 10:30:00' (length=19)
'recurrence-id' => string '20270117T093000Z' (length=16)
'sequence' => int 33
34 =>
array (size=4)
'dtstart' => string '2027-01-24 08:30:00' (length=19)
'dtend' => string '2027-01-24 09:30:00' (length=19)
'recurrence-id' => string '20270124T083000Z' (length=16)
'sequence' => int 34
35 =>
array (size=4)
'dtstart' => string '2027-01-24 09:30:00' (length=19)
'dtend' => string '2027-01-24 10:30:00' (length=19)
'recurrence-id' => string '20270124T093000Z' (length=16)
'sequence' => int 35
36 =>
array (size=4)
'dtstart' => string '2027-01-31 08:30:00' (length=19)
'dtend' => string '2027-01-31 09:30:00' (length=19)
'recurrence-id' => string '20270131T083000Z' (length=16)
'sequence' => int 36
37 =>
array (size=4)
'dtstart' => string '2027-01-31 09:30:00' (length=19)
'dtend' => string '2027-01-31 10:30:00' (length=19)
'recurrence-id' => string '20270131T093000Z' (length=16)
'sequence' => int 37
38 =>
array (size=4)
'dtstart' => string '2029-01-07 08:30:00' (length=19)
'dtend' => string '2029-01-07 09:30:00' (length=19)
'recurrence-id' => string '20290107T083000Z' (length=16)
'sequence' => int 38
39 =>
array (size=4)
'dtstart' => string '2029-01-07 09:30:00' (length=19)
'dtend' => string '2029-01-07 10:30:00' (length=19)
'recurrence-id' => string '20290107T093000Z' (length=16)
'sequence' => int 39
40 =>
array (size=4)
'dtstart' => string '2029-01-14 08:30:00' (length=19)
'dtend' => string '2029-01-14 09:30:00' (length=19)
'recurrence-id' => string '20290114T083000Z' (length=16)
'sequence' => int 40
41 =>
array (size=4)
'dtstart' => string '2029-01-14 09:30:00' (length=19)
'dtend' => string '2029-01-14 10:30:00' (length=19)
'recurrence-id' => string '20290114T093000Z' (length=16)
'sequence' => int 41
42 =>
array (size=4)
'dtstart' => string '2029-01-21 08:30:00' (length=19)
'dtend' => string '2029-01-21 09:30:00' (length=19)
'recurrence-id' => string '20290121T083000Z' (length=16)
'sequence' => int 42
43 =>
array (size=4)
'dtstart' => string '2029-01-21 09:30:00' (length=19)
'dtend' => string '2029-01-21 10:30:00' (length=19)
'recurrence-id' => string '20290121T093000Z' (length=16)
'sequence' => int 43
44 =>
array (size=4)
'dtstart' => string '2029-01-28 08:30:00' (length=19)
'dtend' => string '2029-01-28 09:30:00' (length=19)
'recurrence-id' => string '20290128T083000Z' (length=16)
'sequence' => int 44
45 =>
array (size=4)
'dtstart' => string '2029-01-28 09:30:00' (length=19)
'dtend' => string '2029-01-28 10:30:00' (length=19)
'recurrence-id' => string '20290128T093000Z' (length=16)
'sequence' => int 45Results are returned as an array of dtstart, dtend, recurrence-id, and sequence keys:
Y-m-d H:i:s by defaultdtstart of the original event1 for the first event in the recurring sequence, after the original