import {describe, expect, test} from 'bun:test';
import {random} from '../random.js';

describe('Should support negative random numbers', () => {
	test('test with -1', () => expect(random(-1)).toBe(random(-1)));
	test('test with -2', () => expect(random(-2)).toBe(random(-2)));
	test('different seeds should be different randoms', () =>
		expect(random(-2)).not.toBe(random(-1)));
});

test('Random should be deterministic', () => {
	expect(random(1)).toBe(random(1));
	expect(random(2)).toBe(random(2));
	expect(random(2)).not.toBe(random(1));
	expect(random(null)).not.toBe(random(null));
});

describe('Random should be uniform', () => {
	const ITEM_COUNT = 100000;
	const mapped = new Array(ITEM_COUNT).fill(true).map((_a, i) => {
		return random(i);
	});

	const average = mapped.reduce((a, b) => a + b, 0) / mapped.length;

	test('test if average is around 0.5', () => {
		expect(average).toBeLessThan(0.51);
		expect(average).toBeGreaterThan(0.49);
	});

	const tenPercentSections: number[][] = [];
	const stepInterval = 0.1;
	let currentStep = 0;
	while (currentStep < 0.999999) {
		const items = mapped.filter(
			(m) => m >= currentStep && m <= currentStep + stepInterval,
		);
		tenPercentSections.push(items);
		currentStep += stepInterval;
	}

	const ACCURACY = 0.005;
	tenPercentSections.forEach((entries, index) =>
		test(`section ${index} should contain around ${
			ITEM_COUNT * stepInterval
		} entries`, () => {
			expect(entries.length).toBeLessThan(
				ITEM_COUNT * (stepInterval + ACCURACY),
			);
			expect(entries.length).toBeGreaterThan(
				ITEM_COUNT * (stepInterval - ACCURACY),
			);
		}),
	);

	test('test for average distance', () => {
		const distances = mapped
			.map((_a, i) => {
				if (i === 0) {
					return null;
				}

				return Math.abs(mapped[i] - mapped[i - 1]);
			})
			.filter((f) => f !== null) as number[];
		const averageDistance =
			distances.reduce((a, b) => a + b, 0) / distances.length;

		expect(averageDistance).toBeGreaterThan(0.3);
	});
});

test('Random string should be uniform', () => {
	const alphabet = 'abcdefghijlkmnopqrstuvwxyz0123456789';
	const array = new Array(alphabet.length)
		.fill(true)
		.map((_, i) => random(alphabet[i]));
	const average = array.reduce((a, b) => a + b, 0) / array.length;
	expect(average).toBeLessThan(0.55);
	expect(average).toBeGreaterThan(0.45);
});