Allow backdating a routine completion

1 files changed, 35 insertions, 0 deletions

diff --git a/src/lib/shared/temporal.test.ts b/src/lib/shared/temporal.test.ts
new file mode 100644
index 0000000..ef3477a
--- /dev/null
+++ b/src/lib/shared/temporal.test.ts
@@ -0,0 +1,35 @@
+import { describe, expect, it } from 'vitest';
+import { instantFromDay } from './temporal';
+
+// A weekday well inside the year so noon UTC never collides with a clamp.
+const NOW = Temporal.Instant.from('2026-09-20T08:00:00.000Z');
+
+describe('instantFromDay', () => {
+	it('stamps a past day at noon UTC', () => {
+		expect(instantFromDay('2026-09-13', NOW)).toBe('2026-09-13T12:00:00.000Z');
+	});
+
+	it('clamps today to the current instant', () => {
+		expect(instantFromDay('2026-09-20', NOW)).toBe('2026-09-20T08:00:00.000Z');
+	});
+
+	it('keeps a past day that is only hours old as-is', () => {
+		// 21:00 the day before: noon of that day is still in the past.
+		expect(instantFromDay('2026-09-19', NOW)).toBe('2026-09-19T12:00:00.000Z');
+	});
+
+	it('accepts a day a few hours ahead and clamps it to now', () => {
+		const late = Temporal.Instant.from('2026-09-20T22:00:00.000Z');
+		expect(instantFromDay('2026-09-21', late)).toBe('2026-09-20T22:00:00.000Z');
+	});
+
+	it('rejects a day more than a day ahead', () => {
+		expect(instantFromDay('2026-09-22', NOW)).toBeNull();
+	});
+
+	it('rejects malformed and impossible dates', () => {
+		expect(instantFromDay('', NOW)).toBeNull();
+		expect(instantFromDay('hier', NOW)).toBeNull();
+		expect(instantFromDay('2026-02-30', NOW)).toBeNull();
+	});
+});