✨ installments: strictly match total amount

exactly · Oct 18, 2024 · e6ef876 · e6ef876
1 parent 67f1016
commit e6ef876
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Showing 2 changed files with 3 additions and 2 deletions.
diff --git a/src/installments/split.ts b/src/installments/split.ts
@@ -56,6 +56,8 @@ export default function splitInstallments(
     const diffs = sub(installments, mean(installments));
     amounts = sub(amounts, mulDivUp(diffs, weight, WAD));
     amounts = mulDivUp(amounts, totalAmount, sum(amounts));
+    const excess = sum(amounts) - totalAmount;
+    for (let index = 0; index < excess; ++index) amounts[index]! -= 1n; // eslint-disable-line @typescript-eslint/no-non-null-assertion
     error = mean(mulDivUp(abs(diffs), weight, WAD));
   } while (error >= tolerance);
 

diff --git a/test/installments.test.ts b/test/installments.test.ts
@@ -49,8 +49,7 @@ describe("installments", () => {
           );
 
           expect(amounts).toHaveLength(count);
-          expect(sum(amounts)).toBeGreaterThanOrEqual(totalAmount);
-          expect(sum(amounts) - totalAmount).toBeLessThanOrEqual(count);
+          expect(sum(amounts)).toStrictEqual(totalAmount);
           expect(effectiveRate).toBeGreaterThanOrEqual(min(rates));
           expect(effectiveRate).toBeLessThanOrEqual(max(rates));