The Cost Layer Engine

The Cost Layer Engine

Business Central never costs inventory with one average number: every receipt opens a cost layer, every issue consumes layers in a defined order, and a revaluation restates what is still on the shelf. Your job is that machinery distilled to its core: a layer buffer, FIFO and LIFO application, per-issue COGS, and bookkeeping so exact that not a single cent ever appears or vanishes.

Requirements

The starter contains a table "Cost Layer" and an enum "Cost Flow Method" (values FIFO and LIFO). Keep both exactly as shipped — the grading tests seed and read the table and pass the enum values by name:

• "Entry No." — Integer, the primary key
• Quantity — Decimal, the quantity originally received; never changes after the receipt
• "Remaining Quantity" — Decimal, what is still on the layer; 0 means the layer is consumed
• "Unit Cost" — Decimal, the layer's current unit cost; revaluation restates it
• "Remaining Value" — Decimal, the money value of the remaining quantity, always whole cents

Create a codeunit named "Cost Layer Engine" with three public procedures:

procedure PostReceipt(var CostLayer: Record "Cost Layer"; Quantity: Decimal; UnitCost: Decimal): Integer
procedure PostIssue(var CostLayer: Record "Cost Layer"; Quantity: Decimal; Method: Enum "Cost Flow Method"): Decimal
procedure Revalue(var CostLayer: Record "Cost Layer"; EntryNo: Integer; NewUnitCost: Decimal): Decimal

Whenever a rule below says an amount is rounded, it means AL's default Round to 0.01 — to the nearest cent, halves away from zero.

1. PostReceipt appends a new layer and returns its entry no.: one above the highest existing "Entry No." (1 into an empty buffer). The layer stores Quantity and "Remaining Quantity" = the received quantity, "Unit Cost" as given, and "Remaining Value" = the received quantity times the unit cost, rounded.