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

shuffle.test.ts

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`3adbd147` 2026-06-20 Pavel Safronov	1	import { describe, it, expect } from 'vitest';
	2	import { pickRandomScene } from './shuffle';
	3	import { pointInPolygon } from './geo';
	4	import { findEras } from './eras';
	5	import { toHistoricalDate } from './historicalDate';
	6	import type { CalendarRegion, Geometry } from '../types';
	7
	8	// A 10×10 square from (0,0) to (10,10) in [lng, lat].
	9	const square: Geometry = {
	10	type: 'Polygon',
	11	coordinates: [[[0, 0], [10, 0], [10, 10], [0, 10], [0, 0]]],
	12	};
	13
	14	const regions: CalendarRegion[] = [
	15	{
	16	region: { name: 'Square', geo: square },
	17	eras: [
	18	{ name: 'Julian era', start: '1600-01-01', end: '1700-01-01', calendar: 'Julian' },
	19	// A Gregorian era must never be chosen — it is the default shuffle avoids.
	20	{ name: 'Modern', start: '1700-01-01', end: null, calendar: 'Gregorian' },
	21	],
	22	},
	23	];
	24
	25	// A deterministic rng cycling through fixed values.
	26	function seq(values: number[]): () => number {
	27	let i = 0;
	28	return () => values[i++ % values.length];
	29	}
	30
`38f135ad` 2026-06-21 Pavel Safronov	31	// Two calendars where the first (Julian) is used by more eras than the second
	32	// (Persian) — to prove selection is per-calendar, not weighted by era count.
	33	const twoCalendars: CalendarRegion[] = [
	34	{
	35	region: { name: 'A', geo: square },
	36	eras: [
	37	{ name: 'J1', start: '1600-01-01', end: '1650-01-01', calendar: 'Julian' },
	38	{ name: 'J2', start: '1650-01-01', end: '1700-01-01', calendar: 'Julian' },
	39	{ name: 'J3', start: '1700-01-01', end: '1750-01-01', calendar: 'Julian' },
	40	{ name: 'P1', start: '1600-01-01', end: '1700-01-01', calendar: 'Persian' },
	41	],
	42	},
	43	];
	44
`3adbd147` 2026-06-20 Pavel Safronov	45	describe('pickRandomScene', () => {
	46	it('returns null when the dataset has only Gregorian (default) eras', () => {
	47	const onlyGregorian: CalendarRegion[] = [
	48	{ region: { name: 'G', geo: square }, eras: [{ name: 'M', start: null, end: null, calendar: 'Gregorian' }] },
	49	];
	50	expect(pickRandomScene(onlyGregorian, seq([0.5]))).toBeNull();
	51	});
	52
	53	it('lands on a non-Gregorian era, inside the region, within the era span', () => {
	54	const scene = pickRandomScene(regions, seq([0.3]));
	55	expect(scene).not.toBeNull();
	56	if (!scene) return;
	57
`38f135ad` 2026-06-21 Pavel Safronov	58	expect(scene.calendar).toBe('Julian');
`3adbd147` 2026-06-20 Pavel Safronov	59	// The point is inside the region.
	60	expect(pointInPolygon(scene.lat, scene.lng, square)).toBe(true);
	61
	62	// The date resolves to a non-Gregorian era covering it.
	63	const eras = findEras(toHistoricalDate(scene.date), regions[0].eras);
	64	expect(eras.map((e) => e.calendar)).toContain('Julian');
	65	expect(eras.map((e) => e.calendar)).not.toContain('Gregorian');
	66	});
	67
`38f135ad` 2026-06-21 Pavel Safronov	68	it('weights each calendar equally, not by how many eras use it', () => {
	69	// The first rng call selects the calendar from [Julian, Persian]. A low
	70	// value picks the first, a high value the second — regardless of the fact
	71	// that Julian has 3 eras and Persian only 1.
	72	expect(pickRandomScene(twoCalendars, seq([0.1]))?.calendar).toBe('Julian');
	73	expect(pickRandomScene(twoCalendars, seq([0.9]))?.calendar).toBe('Persian');
	74	});
	75
	76	it('skips calendars shown recently', () => {
	77	// With Julian "recent", only Persian is eligible, so any rng yields it.
	78	expect(pickRandomScene(twoCalendars, seq([0.1]), ['Julian'])?.calendar).toBe('Persian');
	79	expect(pickRandomScene(twoCalendars, seq([0.9]), ['Julian'])?.calendar).toBe('Persian');
	80	});
	81
	82	it('falls back to the full set when every calendar is recent', () => {
	83	// Both calendars recent → still returns one rather than null.
	84	const scene = pickRandomScene(twoCalendars, seq([0.1]), ['Julian', 'Persian']);
	85	expect(scene).not.toBeNull();
	86	expect(['Julian', 'Persian']).toContain(scene?.calendar);
	87	});
	88
`3adbd147` 2026-06-20 Pavel Safronov	89	it('produces dates strictly before a bounded era end (half-open)', () => {
	90	// rng near 1 should still keep the day before the end boundary.
	91	const scene = pickRandomScene(regions, seq([0, 0.5, 0.5, 0.999999]));
	92	expect(scene).not.toBeNull();
	93	if (!scene) return;
	94	expect(scene.date.year).toBeLessThan(1700);
	95	});
	96	});