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

describe('computed', () => {
	const add = (a, b) => a + b;
	const square = a => a * a;

	it('returns the value computed from its dependencies', () => {
		const a = observable(0);
		const b = computed(square, [a]);
		const c = computed(add, [a, b]);

		expect(b()).toEqual(0);
		expect(c()).toEqual(0);

		a(1);
		expect(b()).toEqual(1);
		expect(c()).toEqual(2);

		a(2);
		expect(b()).toEqual(4);
		expect(c()).toEqual(6);

		a(3);
		expect(b()).toEqual(9);
		expect(c()).toEqual(12);
	});

	it('only computes when called', () => {
		let runCount = 0;
		let currentValue = 1;
		const a = observable(0);
		const b = computed(
			val => {
				runCount += 1;
				expect(val).toEqual(currentValue);
				return val * val;
			},
			[a]
		);

		a(1);
		expect(runCount).toEqual(0);
		expect(b()).toEqual(1);
		expect(runCount).toEqual(1);
		expect(b()).toEqual(1);
		expect(runCount).toEqual(1);
		currentValue = 3;
		a(3);
		expect(runCount).toEqual(1);
		expect(b()).toEqual(9);
		expect(runCount).toEqual(2);
	});

	it('can be detached', () => {
		const a = observable(2);
		const b = computed(square, [a]);
		const c = computed(add, [a, b]);

		expect(b()).toEqual(4);
		expect(c()).toEqual(6);

		b.detach();

		a(3);
		expect(b()).toEqual(4);
		expect(c()).toEqual(7);
	});
});