Introduction

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Meziantou.Framework.Scheduling computes when something happens: the occurrences of a schedule, from a start date, in the time zone you choose. It supports the two common ways to describe a schedule, and the calendar format that carries recurring events:

Recurrence rules (RRULE), as defined by RFC 5545 (iCalendar) and RFC 2445: FREQ=MONTHLY;BYDAY=-1FR is the last Friday of every month. Calendar applications use them for recurring meetings.
Cron expressions: 0 9 * * MON-FRI is 09:00 every weekday. Job schedulers use them.
iCalendar (.ics) files, which hold events, their recurrence rule and their time zone.

What you can do with it

Enumerate the occurrences of a recurrence rule, from the start of a series. See Recurrence rules.
Find the next run of a cron expression, to schedule a job. See Cron expressions.
Follow the time zone of the user, so a daily meeting stays at 09:00 across daylight saving time changes. See Time zones.
Describe a recurrence rule in words, in English or in French, such as "every month on the last Friday". See Human-readable text.
Read and write iCalendar files, to import events from a calendar application or to export your own. See Reading iCalendar and Writing iCalendar.

Recurrence rule or cron expression?

	Recurrence rule	Cron expression
Typical use	Calendar events, user-facing schedules	Jobs and maintenance tasks
Start of the schedule	A start date (`DTSTART`) that defines the series: intervals and counts are computed from it	None: every matching date is an occurrence
Intervals	Any interval: every 3 weeks, every other month	Steps within a field: every 15 minutes, every 2 hours
End	A number of occurrences (`COUNT`) or an end date (`UNTIL`)	A year field, at most
Interoperability	iCalendar files, calendar applications	Unix cron and job schedulers

Both types implement IRecurrenceRule, so the methods that compute occurrences, such as GetNextOccurrence, work with either.

Principles

Standards-compliant. Recurrence rules follow RFC 5545 strictly: an unknown rule part or a combination the RFC forbids is an error, and the occurrences are the ones the RFC defines.
Deterministic. Results depend on the start date and the time zone you pass, never on the clock or the time zone of the machine.
Lazy. Occurrences are computed as you enumerate them, so a rule without an end is not a problem: take the ones you need.

Namespace

Every type is in the Meziantou.Framework.Scheduling namespace.

Next steps

Getting started: install the package and compute your first occurrences.