Twelve Buckets

Twelve Buckets

The sales team wants a small chart on the customer card: one bar per month for a chosen year, the four quarter totals underneath, and a legend that lists only the months that actually had sales. Behind that chart sits the plainest data structure AL has: a fixed-size array. An array[12] of Decimal is twelve numbered slots, and the numbering runs from 1 to 12 — there is no slot 0 and no slot 13, and touching either is a runtime error. That makes the month number a natural index: Date2DMY with 2 as its second argument turns any date into a number from 1 to 12.

An array parameter declared var arrives holding whatever the caller left in it, so a procedure that fills one has to reset it first. Clear empties an array in one call, ArrayLen tells you how many slots it has, and CompressArray moves every empty text in an array of Text to the end. This task uses all three. Moving values between slots of one array is a plain loop over the slot numbers — CopyArray copies a run of slots into a second array that must be exactly as long as the run, and a plain := between two arrays does not compile.

Requirements

Create a codeunit named "Monthly Buckets" with five public procedures:

procedure MonthlySales(CustomerNo: Code[20]; Year: Integer; var Buckets: array[12] of Decimal)
procedure AddToMonth(var Buckets: array[12] of Decimal; Month: Integer; Amount: Decimal)
procedure QuarterTotals(Buckets: array[12] of Decimal; var Quarters: array[4] of Decimal)
procedure ShiftWindow(var Buckets: array[12] of Decimal; NewMonthTotal: Decimal)
procedure NonEmptyMonthLabels(Buckets: array[12] of Decimal; var Labels: array[12] of Text): Integer

Rules:

1. MonthlySales fills Buckets[1] to Buckets[12] with the customer's sales per calendar month of Year: for every Cust. Ledger Entry whose "Customer No." is CustomerNo and whose "Posting Date" falls in Year, add its "Sales (LCY)" to the bucket of the posting month — January is slot 1, December is slot 12. Entries of other customers and entries posted in any other year — including 31 December of the year before and 1 January of the year after — are ignored. A month without entries ends up at exactly 0.
2. Every array a procedure fills is fully overwritten: whatever Buckets (in MonthlySales), Quarters or Labels held before the call is gone after it. A caller that reuses one array for several calls must never see the previous call's numbers or labels.
3. AddToMonth adds Amount to Buckets[Month], on top of what that bucket already holds, and leaves the other eleven buckets alone. A Month outside 1 to 12 must raise an error with a message that contains must be between 1 and 12 — never clamp it and never silently ignore it. Using AddToMonth inside MonthlySales is a good idea, but not graded.
4. QuarterTotals folds the twelve months into four quarters: Quarters[1] is the sum of months 1 to 3, Quarters[2] of months 4 to 6, Quarters[3] of months 7 to 9 and Quarters[4] of months 10 to 12.
5. ShiftWindow treats Buckets as a rolling twelve-month window and moves it forward by one month: the oldest month in slot 1 drops off, every other slot moves one position towards the front (slot 2 becomes slot 1, slot 3 becomes slot 2, and so on up to slot 12 becoming slot 11), and NewMonthTotal becomes the new slot 12. Mind the direction of the loop: copying slot 2 into slot 1 before slot 3 into slot 2 keeps every value; the other way round overwrites them.
6. NonEmptyMonthLabels builds the legend. A month is non-empty when its bucket is not exactly 0 — a negative month of credit memos counts too. Each non-empty month is labelled with its English three-letter abbreviation: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec. The labels sit in Labels in calendar order, packed from slot 1 with no gap between them, and every slot after the last label is an empty string. The procedure returns the number of labels — 0 for a year without sales, with all twelve slots empty.

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

Example

A customer with sales of 1200 in February, a credit memo of -300 in July and sales of 800 in November of the requested year:

Buckets   [1] 0   [2] 1200   [3] 0   [4] 0   [5] 0   [6] 0   [7] -300   [8] 0   [9] 0   [10] 0   [11] 800   [12] 0
Quarters  [1] 1200   [2] 0   [3] -300   [4] 800
Labels    [1] Feb   [2] Jul   [3] Nov   [4] to [12] empty        returns 3

ShiftWindow(Buckets, 500) on those buckets leaves 1200 in slot 1, -300 in slot 6, 800 in slot 10 and 500 in slot 12, with every other slot at 0.

What the tests check

The grading tests seed customer ledger entries directly with generated amounts, a generated year and posting dates on 1 January, 31 December and a random mid-year month, call MonthlySales, and compare all twelve buckets — the months with entries against their exact sums, every other month against 0. Separate tests post entries on 31 December of the previous year and on 1 January of the following year, and for another customer in the same month, and expect them ignored. Other tests pre-fill the output array with leftover values before calling MonthlySales, QuarterTotals and NonEmptyMonthLabels and expect the leftovers gone. AddToMonth is called with month 1, with a random month on a pre-filled array (that bucket must grow by the amount, the other eleven must not change), and with months 0 and 13, which must fail with the promised message and leave every bucket untouched. QuarterTotals is checked against twelve generated values; ShiftWindow against twelve generated values and a generated new month, every slot compared; NonEmptyMonthLabels against buckets in February, July and November, a negative month, a pre-filled label array, a year of zeros, and a year with sales in all twelve months (every abbreviation from Jan to Dec in calendar order) — labels are compared character for character, the empty trailing slots and the returned count included.

Learn More

• Array methods — declaring an array, and why its indices run from 1 to N.
• System.CopyArray method — copying a run of slots into a second array of exactly that length; read its second example before reaching for it to shift slots.
• System.CompressArray method — moving empty texts to the end of an array so a printed list has no holes.
• System.Date2DMY method — pulling the day, month or year out of a date.