add money tracker

src/lib/money-tracker/charts.test.ts

@@ -0,0 +1,62 @@
+import { describe, expect, it } from 'vitest';
+import { accountBalances, balanceSeries, forecastSeries, utilityEstimate } from './charts';
+
+describe('money tracker calculations', () => {
+	it('keeps balances separate across accounts and preserves transaction order', () => {
+		const accounts = [
+			{ id: 1, name: 'Cash', openingBalanceCents: 10000 },
+			{ id: 2, name: 'Bank', openingBalanceCents: 20000 }
+		];
+		const transactions = [
+			{ accountId: 1, date: '2026-01-01', amountCents: -2500 },
+			{ accountId: 2, date: '2026-01-02', amountCents: 5000 },
+			{ accountId: 1, date: '2026-01-03', amountCents: 1000 }
+		];
+		expect([...accountBalances(accounts, transactions).values()]).toEqual([8500, 25000]);
+		expect(balanceSeries(accounts, transactions)[0].points.map((point) => point.value)).toEqual([
+			10000, 7500, 8500
+		]);
+	});
+
+	it('projects only future estimates from the current balance', () => {
+		expect(
+			forecastSeries(
+				10000,
+				[
+					{ date: '2026-01-01', amountCents: -9999 },
+					{ date: '2026-10-01', amountCents: -2500 },
+					{ date: '2026-11-01', amountCents: 5000 }
+				],
+				'2026-09-23'
+			)[0].points.map((point) => point.value)
+		).toEqual([10000, 7500, 12500]);
+	});
+
+	it('compares estimated usage cost with prorated advances', () => {
+		const result = utilityEstimate(
+			[
+				{ kind: 'gas', date: '2026-01-01', reading: '100' },
+				{ kind: 'gas', date: '2026-04-01', reading: '130' }
+			],
+			'gas',
+			'1.2500',
+			2000
+		);
+		expect(result?.usage).toBe(30);
+		expect(result?.estimatedCents).toBe(3750);
+		expect(result?.advancesCents).toBeGreaterThan(5800);
+		expect(
+			utilityEstimate(
+				[
+					{ kind: 'gas', date: '2025-01-01', reading: '0' },
+					{ kind: 'gas', date: '2026-01-01', reading: '100' },
+					{ kind: 'gas', date: '2026-04-01', reading: '130' }
+				],
+				'gas',
+				'1.2500',
+				2000,
+				'2026-01-01'
+			)?.usage
+		).toBe(30);
+	});
+});