import assert from 'node:assert/strict';
import { describe, it } from 'node:test';
import {
	addDays,
	compactDate,
	daysBetween,
	germanDate,
	germanDay,
	germanWeekday,
	isCalendarDate,
	schoolToday,
} from '../src/core/dates.ts';

describe('schoolToday', () => {
	it('is the school\'s date, not the container\'s', () => {
		// 23:30 UTC in January is already tomorrow in Berlin (UTC+1) — the case
		// that would make a nightly briefing prepare the wrong day.
		assert.equal(schoolToday(new Date('2026-01-15T23:30:00Z')), '2026-01-16');
		// And in summer the offset is two hours.
		assert.equal(schoolToday(new Date('2026-07-15T22:30:00Z')), '2026-07-16');
		assert.equal(schoolToday(new Date('2026-07-15T21:30:00Z')), '2026-07-15');
	});
});

describe('addDays and daysBetween', () => {
	it('walks calendar dates across a daylight-saving change', () => {
		// Clocks go forward in the EU on 2026-03-29, so a day of 23 hours lies
		// inside this range.
		assert.equal(addDays('2026-03-28', 2), '2026-03-30');
		assert.equal(daysBetween('2026-03-28', '2026-03-30'), 2);
		// And back again in October.
		assert.equal(addDays('2026-10-24', 2), '2026-10-26');
	});

	it('crosses months and years', () => {
		assert.equal(addDays('2026-12-31', 1), '2027-01-01');
		assert.equal(addDays('2026-01-01', -1), '2025-12-31');
		assert.equal(addDays('2028-02-28', 1), '2028-02-29');
		assert.equal(daysBetween('2026-09-21', '2026-09-18'), -3);
	});

	it('refuses something that is not a calendar date', () => {
		assert.throws(() => addDays('21.09.2026', 1), /YYYY-MM-DD/);
	});
});

describe('calendar date helpers', () => {
	it('recognises real dates only', () => {
		assert.equal(isCalendarDate('2026-09-21'), true);
		assert.equal(isCalendarDate('2026-13-01'), false);
		assert.equal(isCalendarDate('2026-02-30'), false);
		assert.equal(isCalendarDate('2026-9-21'), false);
		assert.equal(isCalendarDate('heute'), false);
	});

	it('formats the way a German timetable reads', () => {
		assert.equal(germanWeekday('2026-09-21'), 'Montag');
		assert.equal(germanWeekday('2026-09-17'), 'Donnerstag');
		assert.equal(germanDay('2026-09-21'), '21.09.2026');
		assert.equal(compactDate('2026-09-21'), 20_260_921);
	});

	it('gives a moment the school\'s day, with its weekday', () => {
		assert.equal(germanDate(new Date('2026-09-14T23:30:00Z')), 'Dienstag, 15.09.2026');
	});
});