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();
	});
});