Terms of Payment

Algorithm

Medium

dates

dateformula

payment-terms

Terms of Payment

An accounts-payable clerk just escalated three invoices: the vendor's portal says they fall due two days later than your system does, and one early-payment discount was refused that she swears was earned. Every invoice in Business Central carries a due date and a discount date, both computed from compact date-formula expressions stored on the payment terms — <14D>, <CM+1M>, <-WD2> — and the disagreements always surface at the nasty spots: months of different lengths, leap years, and weekday-based terms. You will build that calculator and get every calendar edge right.

Requirements

Create a codeunit named "Payment Terms Calculator" with two public procedures:

procedure CalcDueDate(DocumentDate: Date; DueDateFormulaText: Text): Date
procedure QualifiesForDiscount(DocumentDate: Date; PaymentDate: Date; DiscountDateFormulaText: Text): Boolean

How a date-formula text is read — this is the full contract the tests grade:

A formula arrives wrapped in angle brackets (<14D>, <CM+1M>) and contains up to three terms, read left to right; each term moves a running date that starts at DocumentDate, and the final running date is the result.
nD and nW move the running date exactly n days or n weeks forward; a leading - moves backward instead.
nM and nY move to the same day of the month n calendar months or years away; when that day does not exist in the target month, the result is the last day of the target month — 31 January plus 1M is 28 February, or 29 February in a leap year, and 1Y applied to 29 February 2024 is 28 February 2025.
CM jumps the running date forward to the last day of its own month.
WDn (weekday n, Monday = 1 through Sunday = 7) jumps forward to the next date falling on that weekday, always moving by at least one day — so <WD2> on a date that is already a Tuesday lands a full week later; -WDn jumps backward to the previous such date, always moving back by at least one day.
Terms apply strictly in the order written: <CM+1M> is month-end first, then one month — from 15 February 2024 that is 29 March 2024 — while <1M+CM> from the same date gives 31 March 2024. The tests grade this distinction.
Blank text means due immediately: CalcDueDate returns DocumentDate unchanged.
Text that is not a valid date formula must raise an error, and the error message must include the rejected text.

QualifiesForDiscount applies DiscountDateFormulaText to DocumentDate under exactly the same rules to get the discount date, and returns true when PaymentDate falls on or before that date — paying on the discount date itself still earns the discount.

What you may rely on — the tests never violate this: every formula the tests pass is blank, deliberately invalid, or built only from the term forms above; the number in a term never exceeds 300; all dates are ordinary dates well inside the supported calendar.

What the tests check

Fixed calendar cases check each rule above — a plain day offset, month steps clamping into February of a common year and of a leap year, <1Y> off a leap day, both orderings of CM and 1M from 15 February 2024, a <CM-10D> combination, a three-term <CM+1M-10D> combination, the next-Tuesday and previous-Tuesday weekday jumps including the full-week move in each direction when the start date is already a Tuesday, blank text, and the invalid-text error (matched as a substring on the rejected text). QualifiesForDiscount is graded on, before, and after the discount date. Finally, randomized day and week offsets are checked against plain calendar arithmetic, so hardcoding the fixed examples fails.

Learn More

Hint 1

Month arithmetic is where hand-rolled calendars die: one month past 31 January must clamp to 28 — or 29 — February, and a year past a leap day clamps too. Before you write day-count loops, notice that this notation is not invented for the task: it is exactly what sits in the Due Date Calculation field of every payment terms record.

Hint 2

The platform has a dedicated data type for these expressions and a system method that applies one to a reference date — month-end clamping, leap years, left-to-right term order, and the always-move-at-least-a-day weekday rule all come with it. Blank input is a valid, empty formula to that method.

Hint 3

Convert the incoming text into a DateFormula variable with Evaluate — a failed Evaluate is precisely your invalid-text signal, so raise your own error that names the text — then hand the formula and the document date to CalcDate. The discount check is one on-or-before comparison against the same calculation.

ALBusiness Central 28.4

Press Compile to check your code compiles — Submit runs the tests.

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