import { describe, expect, it } from 'vitest';
import { flingDir, pushSample, type Sample } from './fling';

/** A straight drag from (0,0) by (dx,dy) over `ms`, sampled every 16 ms. */
function drag(dx: number, dy: number, ms: number): Sample[] {
	const out: Sample[] = [];
	for (let t = 0; t <= ms; t += 16) pushSample(out, { x: (dx * t) / ms, y: (dy * t) / ms, t });
	return out;
}

describe('flingDir', () => {
	it('maps a flick to the side it reveals', () => {
		expect(flingDir(drag(-200, 0, 96))).toBe('right');
		expect(flingDir(drag(200, 0, 96))).toBe('left');
		expect(flingDir(drag(0, -200, 96))).toBe('down');
		expect(flingDir(drag(0, 200, 96))).toBe('up');
	});

	it('ignores slow drags', () => {
		expect(flingDir(drag(-200, 0, 800))).toBeNull();
	});

	it('ignores diagonal flicks', () => {
		expect(flingDir(drag(-200, -150, 96))).toBeNull();
	});

	it('ignores a drag that stops before lifting', () => {
		const s = drag(-300, 0, 96);
		const end = s.at(-1)!;
		for (let t = 16; t <= 160; t += 16) pushSample(s, { ...end, t: end.t + t });
		expect(flingDir(s)).toBeNull();
	});

	it('needs at least two samples', () => {
		expect(flingDir([])).toBeNull();
		expect(flingDir([{ x: 0, y: 0, t: 0 }])).toBeNull();
	});

	it('keeps the trail short', () => {
		const s = drag(-2000, 0, 2000);
		expect(s.at(-1)!.t - s[0].t).toBeLessThanOrEqual(216);
	});
});