import { createDebouncedStorage } from '../store/debouncedStorage';

const makeBase = () => ({
    getItem: jest.fn(async (_name: string): Promise<string | null> => 'from-disk'),
    setItem: jest.fn(async (_name: string, _value: string) => {}),
    removeItem: jest.fn(async (_name: string) => {}),
});

beforeEach(() => {
    jest.useFakeTimers();
});
afterEach(() => {
    jest.useRealTimers();
});

describe('createDebouncedStorage', () => {
    it('collapses a burst of writes into one trailing write with the latest value', () => {
        const base = makeBase();
        const storage = createDebouncedStorage(base, 400);

        storage.setItem('k', '1');
        jest.advanceTimersByTime(300);
        storage.setItem('k', '2');
        jest.advanceTimersByTime(300);
        storage.setItem('k', '3');
        expect(base.setItem).not.toHaveBeenCalled();

        jest.advanceTimersByTime(400);
        expect(base.setItem).toHaveBeenCalledTimes(1);
        expect(base.setItem).toHaveBeenCalledWith('k', '3');
    });

    it('reads a pending value before it reaches the disk, and falls back to the base storage', async () => {
        const base = makeBase();
        const storage = createDebouncedStorage(base);

        await expect(storage.getItem('k')).resolves.toBe('from-disk');
        storage.setItem('k', 'fresh');
        await expect(storage.getItem('k')).resolves.toBe('fresh');
    });

    it('flush writes immediately and cancels the timer', async () => {
        const base = makeBase();
        const storage = createDebouncedStorage(base);

        storage.setItem('a', '1');
        storage.setItem('b', '2');
        await storage.flush();
        expect(base.setItem.mock.calls).toEqual([['a', '1'], ['b', '2']]);

        jest.advanceTimersByTime(1000);
        expect(base.setItem).toHaveBeenCalledTimes(2);
    });

    it('flush with nothing pending does not write', async () => {
        const base = makeBase();
        await createDebouncedStorage(base).flush();
        expect(base.setItem).not.toHaveBeenCalled();
    });

    it('removeItem drops a pending write and removes from the base storage', async () => {
        const base = makeBase();
        const storage = createDebouncedStorage(base);

        storage.setItem('k', '1');
        await storage.removeItem('k');
        jest.advanceTimersByTime(1000);

        expect(base.setItem).not.toHaveBeenCalled();
        expect(base.removeItem).toHaveBeenCalledWith('k');
    });
});