FA-58094 / Double-entry ledger accounting / Member archive

FIFO perpetual inventory journal: layer merge target · case 04

New purchases jump the FIFO queue when their cost matches the oldest layer.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

x = [['buy', qty, unit_cost] | ['sell', qty, unit_price] | ['purchase_return', qty, unit_cost]]. Layers are kept oldest first; a buy at the same cost as the newest layer merges into it. A sale consumes layers oldest first (COGS) and records revenue; a sale exceeding on-hand quantity is rejected whole. A purchase return removes qty from the newest layer at that cost holding at least qty, else it is rejected. Emptied layers are removed. Return {'cogs', 'revenue', 'inventory': sum qty*cost, 'layers', 'rejected': event indexes}.

Why this case matters

Ledger software must keep debits equal to credits and apply normal-balance, period and cutoff rules exactly; small sign or boundary slips silently misstate financial statements.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: layer merge target	`{"cogs": 540, "inventory": 1860, "layers": [[8, 120], [3, 100], [1, 100], [5, 100]], "rejected": [3], "revenue": 800}`	`{"cogs": 540, "inventory": 1960, "layers": [[8, 120], [1, 100], [2, 150], [6, 100]], "rejected": [3], "revenue": 800}`	Failed

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