import { renderHook, act } from '@testing-library/react-hooks';
import { useState, useRef, useEffect } from 'react';

function usePrevious<T>(value: T): T | undefined {
	const ref = useRef<T>();
	useEffect(() => {
		ref.current = value;
	}, [value]);
	return ref.current;
}
describe('usePrevious', () => {
	it('should return the previous value', () => {
		const { result } = renderHook(() => {
			const [count, setCount] = useState(0);
			const previousCount = usePrevious(count);

			return { count, previousCount, setCount };
		});

		act(() => {
			result.current.setCount(5);
		});

		expect(result.current.count).toBe(5);
		expect(result.current.previousCount).toBe(0);

		act(() => {
			result.current.setCount(10);
		});

		expect(result.current.count).toBe(10);
		expect(result.current.previousCount).toBe(5);
	});

	it('should return undefined if there is no previous value', () => {
		const { result } = renderHook(() => {
			const [count, setCount] = useState(0);
			const previousCount = usePrevious(count);

			return { count, previousCount, setCount };
		});

		expect(result.current.count).toBe(0);
		expect(result.current.previousCount).toBeUndefined();

		act(() => {
			result.current.setCount(5);
		});

		expect(result.current.count).toBe(5);
		expect(result.current.previousCount).toBe(0);
	});
});