Fix leftover balance usage in budget covering logic (#7131) (#7272)

* Fix leftover balance usage in budget covering logic (#7131)

* [autofix.ci] apply automated fixes

* Add regression unit tests for `coverOverbudgeted` fixes

* Update release note for a more user-facing sentence

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

packages/loot-core/src/server/budget/actions.test.ts

@@ -0,0 +1,99 @@
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+
+import * as db from '../db';
+import * as sheet from '../sheet';
+
+import {
+  coverOverbudgeted,
+  getSheetValue,
+  setBudget,
+  setCategoryCarryover,
+} from './actions';
+import * as budget from './base';
+
+describe('coverOverbudgeted', () => {
+  beforeEach(global.emptyDatabase());
+  afterEach(global.emptyDatabase());
+
+  it('fully covers the overbudget when category has sufficient leftover', async () => {
+    // Setup: cat1 has 100 leftover, overbudget is 90
+    await prepareDatabase();
+
+    await coverOverbudgeted({
+      month: '2024-02',
+      category: 'cat1',
+      currencyCode: 'USD',
+    });
+    await sheet.waitOnSpreadsheet();
+
+    const sheetName = 'budget202402';
+    expect(await getSheetValue(sheetName, 'to-budget')).toBe(0);
+    expect(await getSheetValue(sheetName, 'leftover-cat1')).toBe(10);
+  });
+
+  it('partially covers the overbudget when category leftover is insufficient', async () => {
+    // Setup: cat3 has 10 leftover, overbudget is 90
+    await prepareDatabase();
+
+    await coverOverbudgeted({
+      month: '2024-02',
+      category: 'cat3',
+      currencyCode: 'USD',
+    });
+    await sheet.waitOnSpreadsheet();
+
+    const sheetName = 'budget202402';
+    expect(await getSheetValue(sheetName, 'to-budget')).toBe(-80);
+    expect(await getSheetValue(sheetName, 'leftover-cat3')).toBe(0);
+  });
+});
+
+// Setup: 2024-02, is 90 overbudgeted
+// with balances of cat1 = 100, cat2 = -20, cat3 = 10
+async function prepareDatabase() {
+  await db.insertCategoryGroup({
+    id: 'income-group',
+    name: 'Income',
+    is_income: 1,
+  });
+  await db.insertCategory({
+    id: 'income-cat',
+    name: 'Income',
+    cat_group: 'income-group',
+    is_income: 1,
+  });
+
+  await db.insertCategoryGroup({ id: 'group1', name: 'group1', is_income: 0 });
+  await db.insertCategory({
+    id: 'cat1',
+    name: 'cat1',
+    cat_group: 'group1',
+    is_income: 0,
+  });
+  await db.insertCategory({
+    id: 'cat2',
+    name: 'cat2',
+    cat_group: 'group1',
+    is_income: 0,
+  });
+  await db.insertCategory({
+    id: 'cat3',
+    name: 'cat3',
+    cat_group: 'group1',
+    is_income: 0,
+  });
+
+  await setBudget({ category: 'cat1', month: '2024-01', amount: 100 });
+  await setBudget({ category: 'cat2', month: '2024-01', amount: -20 });
+  await setBudget({ category: 'cat3', month: '2024-01', amount: 10 });
+
+  await sheet.loadSpreadsheet(db);
+  await budget.createBudget(['2024-01', '2024-02']);
+
+  await setCategoryCarryover({
+    startMonth: '2024-01',
+    category: 'cat2',
+    flag: true,
+  });
+  await sheet.waitOnSpreadsheet();
+}

packages/loot-core/src/server/budget/actions.ts

@@ -520,6 +520,10 @@ export async function coverOverbudgeted({
 }): Promise<void> {
   const sheetName = monthUtils.sheetForMonth(month);
   const categoryBudget = await getSheetValue(sheetName, 'budget-' + category);
+  const categoryLeftover = await getSheetValue(
+    sheetName,
+    'leftover-' + category,
+  );
 
   // Cover provided amount (can be partial) or full overbudgeted amount.
   const amountToCover = amount
@@ -527,12 +531,12 @@ export async function coverOverbudgeted({
       -amount
     : await getSheetValue(sheetName, 'to-budget');
 
-  if (amountToCover >= 0 || categoryBudget <= 0) {
+  if (amountToCover >= 0 || categoryLeftover <= 0) {
     return;
   }
 
-  // Don't allow the budget of the covering category to go negative.
-  const coverableAmount = Math.min(Math.abs(amountToCover), categoryBudget);
+  // Don't exceed the available balance of the covering category.
+  const coverableAmount = Math.min(Math.abs(amountToCover), categoryLeftover);
 
   await batchMessages(async () => {
     await setBudget({

upcoming-release-notes/7272.md

@@ -0,0 +1,6 @@
+---
+category: Bugfixes
+authors: [JSkinnerUK]
+---
+
+Fixed an issue that prevented category's leftover from being able to cover an overbudgeted amount.