when-am-i / files / src / utils / dateRange.test.ts

dateRange.test.ts

1	import { describe, it, expect } from 'vitest';
2	import { deriveMinYear } from './dateRange';
3	import type { CalendarRegion, Era } from '../types';
4
5	const WORLD_GEO = { type: 'Polygon' as const, coordinates: [[[0, 0], [1, 0], [1, 1], [0, 0]] as [number, number][]] };
6
7	function regionWith(eras: Era[]): CalendarRegion {
8	return { region: { name: 'Test', geo: WORLD_GEO }, eras };
9	}
10
11	describe('deriveMinYear', () => {
12	it('falls back to 2000 BCE when no era has a dated start', () => {
13	const regions = [regionWith([{ name: 'Open', start: null, end: null, calendar: 'Gregorian' }])];
14	expect(deriveMinYear(regions, 2026)).toBe(-1999);
15	});
16
17	it('uses the oldest dated start across all regions, minus a 10% margin', () => {
18	const regions = [
19	regionWith([{ name: 'A', start: '1700-01-01', end: null, calendar: 'Gregorian' }]),
20	regionWith([{ name: 'B', start: '-0036-01-01', end: null, calendar: 'Maya Long Count' }]),
21	];
22	// oldest = -36; span to 2026 = 2062; margin = 206.2 → floor(-36 - 206.2) = -243
23	expect(deriveMinYear(regions, 2026)).toBe(-243);
24	});
25
26	it('ignores null-start eras even when other eras in the same region are dated', () => {
27	const regions = [
28	regionWith([
29	{ name: 'Open', start: null, end: '1000-01-01', calendar: 'Hebrew' },
30	{ name: 'Dated', start: '500-01-01', end: null, calendar: 'Gregorian' },
31	]),
32	];
33	// oldest dated = 500; span to 2026 = 1526; margin = 152.6 → floor(500 - 152.6) = 347
34	expect(deriveMinYear(regions, 2026)).toBe(347);
35	});
36	});