import throttle from 'lodash.throttle';
import { useCallback, useEffect } from 'react'

export const BackToTopButton = () => {
  useEffect(() => {
    // ====== scroll top js
    function scrollTo(element, to = 0, duration = 500) {
      const start = element.scrollTop;
      const change = to - start;
      const increment = 20;
      let currentTime = 0;

      const animateScroll = () => {
        currentTime += increment;

        const val = Math.easeInOutQuad(currentTime, start, change, duration);

        element.scrollTop = val;

        if (currentTime < duration) {
          setTimeout(animateScroll, increment);
        }
      };

      animateScroll();
    }

    Math.easeInOutQuad = function (t, b, c, d) {
      t /= d / 2;
      if (t < 1) return (c / 2) * t * t + b;
      t--;
      return (-c / 2) * (t * (t - 2) - 1) + b;
    };
    const backToTop = document.querySelector('.back-to-top')
    if (backToTop) {
      backToTop.onclick = () => {
        scrollTo(document.documentElement);
      };
    }

    window.addEventListener('scroll', navBarScollListener)
    return () => {
      window.removeEventListener('scroll', navBarScollListener)
    }
  }, [])

  // 滚动监听
  const throttleMs = 200
  const navBarScollListener = useCallback(
    throttle(() => {
      const scrollY = window.scrollY;
      // 显示或隐藏返回顶部按钮
      const backToTop = document.querySelector('.back-to-top');
      if (backToTop) {
        backToTop.style.display = scrollY > 50 ? 'flex' : 'none';
      }
    }, throttleMs)
  )

  return <>
        {/* <!-- ====== Back To Top Start --> */}
        <a className="back-to-top fixed bottom-16 left-auto right-8 z-[999] hidden h-10 w-10 items-center justify-center rounded-md bg-primary text-white shadow-md transition duration-300 ease-in-out hover:bg-dark">
            <span className="mt-[6px] h-3 w-3 rotate-45 border-l border-t border-white" ></span>
         </a>
    {/* <!-- ====== Back To Top End --> */}
    </>
}