Next N Occurrences

Next N Occurrences

Operations wants one planner for every recurring job in the company: the cycle count runs every Monday, Wednesday and Friday at 06:00; the subscription invoices go out on the last Friday of each month at 17:00. You are building the module that answers the only question anyone ever asks a schedule: when does it fire next?

Requirements

The starter declares an enum "Recurrence Ordinal" with the values First, Second, Third, Fourth, Last — keep its name and values exactly as given, since the tests bind to them.

Create a codeunit named "Recurrence Planner" with four public procedures:

procedure CreateWeekly(StartDate: Date; StartTime: Time; Weekdays: List of [Integer]; EndDate: Date)
procedure CreateMonthlyByDayOfWeek(StartDate: Date; StartTime: Time; Ordinal: Enum "Recurrence Ordinal"; Weekday: Integer; EndDate: Date)
procedure CalculateNextOccurrence(LastOccurrence: DateTime): DateTime
procedure NextOccurrences(FromDateTime: DateTime; MaxCount: Integer): List of [DateTime]

A planner instance holds one schedule at a time: each Create call defines the schedule and replaces whatever schedule the same instance held before.

Weekday numbers run 1 (Monday) through 7 (Sunday) — the numbering Date2DWY uses.

Every occurrence of a schedule happens at StartTime; which dates carry an occurrence depends on how the schedule was created:

• CreateWeekly: every date from StartDate onward whose weekday number is in Weekdays is an occurrence date.
• CreateMonthlyByDayOfWeek: every calendar month has exactly one candidate date — the first, second, third, fourth or last date in that month whose weekday number is Weekday, as picked by Ordinal. Every candidate date on or after StartDate is an occurrence date. Note that Fourth and Last are not the same thing: in a month with five Fridays, the fourth Friday and the last Friday are a week apart.
• In both kinds, when EndDate is not 0D the schedule ends there: a date on EndDate still carries an occurrence; any later date does not. When EndDate is 0D the schedule never ends.

CalculateNextOccurrence returns the earliest occurrence DateTime that is strictly later than LastOccurrence — so passing an occurrence's own DateTime returns the one after it, and passing 0DT returns the very first occurrence of the schedule. Note the same-day case: when LastOccurrence falls on an occurrence date but earlier in the day than StartTime, that same day's occurrence is still ahead and must be returned. When no occurrence remains before the schedule ends, return 0DT. If it is called before any Create procedure has run on the instance, raise an error with a message that contains the text No schedule has been created.

NextOccurrences returns the occurrences strictly later than FromDateTime in ascending order — at most MaxCount of them, fewer when the schedule ends first, an empty list when nothing remains at all. If MaxCount is below 1, raise an error with a message that contains the text at least one occurrence.

What you may rely on — the tests never violate this:

• Weekdays holds between 1 and 7 distinct values, each 1 to 7; it is never empty.
• Weekday is a single value from 1 to 7.
• StartDate and StartTime are always set; EndDate is either 0D or on/after StartDate.
• LastOccurrence and FromDateTime can be any DateTime, including 0DT and moments far before StartDate or far after EndDate.

Pick object IDs in the range 50100–50199 and reference other objects by name, never by ID.

What the tests check

The tests assert exact DateTime sequences from fixed anchors in 2026: the first occurrence and the five-element sequence of a Monday-Wednesday-Friday weekly plan, an anchor that starts on an unscheduled weekday, a query from a moment weeks before StartDate that must yield the anchor's occurrence and never an earlier date, the strictly-after rule from an occurrence's own DateTime and from an earlier moment on the same day, the EndDate boundary from both sides in both schedule kinds — including a monthly candidate landing exactly on EndDate — a never-ending schedule queried years past its anchor, NextOccurrences stopping early at the schedule's end, all five ordinals (first-Monday and last-Friday sequences across months, a second-Tuesday and a third-Wednesday pick, and the fourth-versus-last Friday split in a five-Friday month), a monthly anchor that has already passed its month's candidate, a second Create call replacing the first schedule, and both error rules against the exact message fragments quoted above. One test builds a randomized weekly schedule — random anchor date, time of day, weekday set and end date — and compares your output element by element against an independent day-by-day walk over the calendar, so hardcoding the fixed examples will not pass.

Learn More

• DateTime data type — what 0DT means and how DateTime values compare.
• System.CreateDateTime(Date, Time) Method — joining a date and a time into one DateTime.
• System.DT2Date(DateTime) Method — splitting the date back out of a DateTime.
• System.Date2DWY(Date, Integer) Method — the weekday numbering the schedule contract uses.