FA-59623 / Subscription proration billing / Member archive

Sequential plan changes within one cycle: change window · case 03

Changes timestamped before the period start produce prorations larger than the period price.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input {start, end, initial price, changes: [[t, price]]}. Changes are ordered by time; at equal times only the last applies. A change outside [start, end) or to the current price is ignored. Each effective change emits a credit line -(current*(end-t)/span) and a debit line new*(end-t)/span, magnitudes half-up, and the new price becomes current. Return the list of line amounts.

Why this case matters

Customers who change plans several times in a cycle must be credited for the plan they actually had at each change.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression 0	`[-2200, 5500, -4333, 4040, -2486, 3733]`	`[-1733, 4040, -2486, 3733]`	Failed

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