import { debounce } from "../debounce";

describe("debounce", () => {
  beforeEach(() => {
    jest.useFakeTimers();
  });
  afterEach(() => {
    jest.useRealTimers();
  });

  it("collapses rapid calls into a single trailing invocation", () => {
    const fn = jest.fn();
    const debounced = debounce(fn, 100);
    debounced("a");
    debounced("b");
    debounced("c");
    expect(fn).not.toHaveBeenCalled();
    jest.advanceTimersByTime(100);
    expect(fn).toHaveBeenCalledTimes(1);
    expect(fn).toHaveBeenCalledWith("c");
  });

  it("cancels a pending invocation when cancel() runs first", () => {
    const fn = jest.fn();
    const debounced = debounce(fn, 100);
    debounced("a");
    debounced.cancel();
    jest.advanceTimersByTime(200);
    expect(fn).not.toHaveBeenCalled();
  });

  it("re-arms after a successful invocation", () => {
    const fn = jest.fn();
    const debounced = debounce(fn, 50);
    debounced("a");
    jest.advanceTimersByTime(50);
    debounced("b");
    jest.advanceTimersByTime(50);
    expect(fn).toHaveBeenCalledTimes(2);
    expect(fn.mock.calls.map((c) => c[0])).toEqual(["a", "b"]);
  });
});