Money tracker: vertical month/year gridlines on wealth chart, keep range in ?range= URL param

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

@@ -4,6 +4,9 @@ import {
 	accountColor,
 	balanceSeries,
 	forecastSeries,
+	parseHistoryRange,
+	timeGrid,
+	yearLabels,
 	utilityEstimate,
 	wealthProjection,
 	wealthTimeline
@@ -308,4 +311,42 @@ describe('history range', () => {
 		expect(byAccount.map((line) => line.label)).toEqual(['Bank', 'Parents', 'Total']);
 		expect(byAccount.at(-1)!.points[0].value).toBe(1000);
 	});
+
+	it('reads the history range from the URL, defaulting to one year', () => {
+		expect(parseHistoryRange('3y')).toBe('3y');
+		expect(parseHistoryRange('all')).toBe('all');
+		expect(parseHistoryRange('1y')).toBe('1y');
+		expect(parseHistoryRange('5y')).toBe('1y');
+		expect(parseHistoryRange(null)).toBe('1y');
+	});
+
+	it('puts a gridline on every month start and marks 1 January as a year line', () => {
+		const lines = timeGrid('2025-10-24', '2026-03-01', 'months');
+		expect(lines).toEqual([
+			{ date: '2025-11-01', year: false },
+			{ date: '2025-12-01', year: false },
+			{ date: '2026-01-01', year: true },
+			{ date: '2026-02-01', year: false },
+			{ date: '2026-03-01', year: false }
+		]);
+		expect(timeGrid('2025-01-01', '2025-02-15', 'months').map((line) => line.date)).toEqual([
+			'2025-01-01',
+			'2025-02-01'
+		]);
+	});
+
+	it('puts only year lines on the all-time grid and thins crowded year labels', () => {
+		const lines = timeGrid('2007-02-01', '2027-10-24', 'years');
+		expect(lines).toHaveLength(20);
+		expect(lines.every((line) => line.year && line.date.endsWith('-01-01'))).toBe(true);
+		expect(lines[0].date).toBe('2008-01-01');
+		expect(yearLabels(lines, 30)).toHaveLength(20);
+		expect(yearLabels(lines, 6).map((date) => date.slice(0, 4))).toEqual([
+			'2010',
+			'2015',
+			'2020',
+			'2025'
+		]);
+		expect(timeGrid('2026-01-02', '2026-01-01', 'months')).toEqual([]);
+	});
 });