import { useCallback, useEffect, useMemo, useRef, useState } from "react";

interface ScrollTrackerResult {
  isScrollable: boolean;
  isAtTop: boolean;
  isAtBottom: boolean; 
}

function useScrollTracker(ref: React.RefObject<HTMLElement>): ScrollTrackerResult {
  const [isScrollable, setIsScrollable] = useState(false);
  const [isAtTop, setIsAtTop] = useState(true);
  const [isAtBottom, setIsAtBottom] = useState(false);

  const getScrollState = useCallback(() => {
    if (ref.current) {
      const { scrollTop, scrollHeight, clientHeight } = ref.current;

      setIsScrollable(scrollHeight > clientHeight);
      setIsAtTop(scrollTop === 0);
      setIsAtBottom(scrollTop + clientHeight >= scrollHeight);
    }
  }, [ref]);

  const debouncedGetScrollState = useRef(debounce(getScrollState, 100));

  useEffect(() => {
    const element = ref.current;

    if (element) {
      element.addEventListener("scroll", debouncedGetScrollState.current);

      return () => element.removeEventListener("scroll", 
        debouncedGetScrollState.current);
    }
  }, [debouncedGetScrollState]);

  const state: ScrollTrackerResult = useMemo(() => ({
    isScrollable, 
    isAtTop,
    isAtBottom
  }), [isScrollable, isAtTop, isAtBottom]);

  return state;
}

function debounce(fn: () => any, delayMs = 100) {
  let timeout: any;
  return () => {
    clearTimeout(timeout);
    timeout = setTimeout(fn, delayMs);
  }
}

export default useScrollTracker;