const { observable } = require('../lib/index.js');

describe('observable', () => {
	it('returns its initialized value', () => {
		const a = observable(true);
		expect(a()).toEqual(true);
	});

	it('returns its set value', () => {
		const a = observable();
		expect(a()).toEqual(undefined);
		expect(a(true)).toEqual(true);
	});

	it('returns notifies dependents of updates', () => {
		let runCount = 0;
		let currentValue = 1;
		const a = observable();
		a.subscribe(val => {
			runCount += 1;
			expect(val).toEqual(currentValue);
		});
		expect(a(1)).toEqual(1);
		expect(runCount).toEqual(1);
		expect(a(1)).toEqual(1);
		expect(runCount).toEqual(1);
		currentValue = 2;
		expect(a(2)).toEqual(2);
		expect(runCount).toEqual(2);
		expect(a(2)).toEqual(2);
		expect(runCount).toEqual(2);
		currentValue = 1;
		expect(a(1)).toEqual(1);
		expect(runCount).toEqual(3);
		expect(a(1)).toEqual(1);
		expect(runCount).toEqual(3);
	});

	it('honors cancelled subscriptions', () => {
		let runCount = 0;
		let currentValue = 1;
		const a = observable();
		const cancelSubscription = a.subscribe(val => {
			runCount += 1;
			expect(val).toEqual(currentValue);
		});
		const cancelSubscription2 = a.subscribe(val => {
			runCount += 1;
			expect(val).toEqual(currentValue);
		});
		expect(a(1)).toEqual(1);
		expect(runCount).toEqual(2);
		expect(a(1)).toEqual(1);
		expect(runCount).toEqual(2);
		expect(cancelSubscription()).toEqual(1);
		currentValue = 3;
		expect(a(3)).toEqual(3);
		expect(runCount).toEqual(3);
		expect(cancelSubscription2()).toEqual(0);
		currentValue = 4;
		expect(a(4)).toEqual(4);
		expect(runCount).toEqual(3);
	});

	it('uses a comparator', () => {
		function setEquals(a, b) {
			return (
				a instanceof Set &&
				b instanceof Set &&
				[...a].reduce((acc, d) => acc && b.has(d), true) &&
				[...b].reduce((acc, d) => acc && a.has(d), true)
			);
		}

		let runCount = 0;

		const a = observable(new Set([1, 2]), setEquals);
		a.subscribe(() => (runCount += 1));
		expect([...a()]).toEqual([1, 2]);
		expect(runCount).toEqual(0);
		expect([...a(new Set([2, 1]))]).toEqual([1, 2]);
		expect(runCount).toEqual(0);
		expect([...a(new Set([3, 2, 1]))]).toEqual([3, 2, 1]);
		expect(runCount).toEqual(1);
	});
});