export class ScrollHandler {
  constructor() {
    this.lastScrollTop = 0;
    this.scrollDownCallbacks = [];
    this.scrollUpCallbacks = [];
    window.addEventListener(
      'scroll',
      () => {
        const st = window.pageYOffset || document.documentElement.scrollTop;
        if (st > this.lastScrollTop) {
          this.scrollDownCallbacks.forEach((cb) => cb(st));
        } else {
          this.scrollUpCallbacks.forEach((cb) => cb(st));
        }
        this.lastScrollTop = st <= 0 ? 0 : st;
      },
      false,
    );
  }

  onScrollDown(cb) {
    this.scrollDownCallbacks.push(cb);
  }

  onScrollUp(cb) {
    this.scrollUpCallbacks.push(cb);
  }
}

const scrollHandler = new ScrollHandler();

export default scrollHandler;