useDropdownAttributes.ts

import { ComputedRef, Ref, ref, watch } from 'vue';

export const useDropdownAttributes = () => {
  const dropdownWidth = ref('');
  const dropdownTop = ref('');
  const dropdownBottom = ref('');
  const dropdownLeft = ref('');
  const isDirectedUpwards = ref(false);
  const togglerRect = ref<DOMRect>();
  const dropdownRect = ref<DOMRect>();

  const PADDING_ALLOWANCE = 8;

  const getFirstScrollableParent = (element: HTMLElement | null): HTMLElement => {
    const parentElement = element?.parentElement;
    if (!parentElement) return document.body;

    const overflowY = window.getComputedStyle(parentElement).overflowY;

    if (overflowY === 'scroll' || overflowY === 'auto') return parentElement;

    return getFirstScrollableParent(parentElement);
  };

  const autodetectPosition = (
    isDropdownDisplayed: Ref<boolean>,
    togglerElement: HTMLElement | null = null,
    dropdownElement: HTMLElement | null = null,
    dropdownContent: Ref<unknown> | ComputedRef<unknown> = ref([]),
    isUpwardPreferred = false,
  ) => {
    if (!togglerElement || !dropdownElement) return;

    const updateDropdownAttributes = () => {
      togglerRect.value = togglerElement.getBoundingClientRect();
      dropdownRect.value = dropdownElement.getBoundingClientRect();
      dropdownWidth.value = `${togglerRect.value.width}px`;
      dropdownBottom.value = `${window.innerHeight - togglerRect.value.top}px`;
      dropdownTop.value = `${
        window.innerHeight - togglerRect.value.bottom - dropdownRect.value.height
      }px`;
      dropdownLeft.value = `${togglerRect.value.left}px`;
    };

    const handleResize = () => {
      requestAnimationFrame(updateDropdownAttributes);
    };

    const handleScroll = () => {
      requestAnimationFrame(updateDropdownAttributes);
    };

    watch(
      [isDropdownDisplayed, dropdownContent],
      ([newVal, _]) => {
        const scrollableParent = getFirstScrollableParent(togglerElement);
        if (!newVal) {
          window.removeEventListener('resize', handleResize);
          window.removeEventListener('scroll', handleScroll);
          scrollableParent.removeEventListener('resize', handleResize);
          scrollableParent.removeEventListener('scroll', handleScroll);
          return;
        }

        requestAnimationFrame(() => {
          const distanceFromBottom =
            window.innerHeight - togglerElement.getBoundingClientRect().bottom;
          const distanceFromTop = togglerElement.getBoundingClientRect().top;
          const dropdownHeight = dropdownElement.offsetHeight;

          isDirectedUpwards.value = isUpwardPreferred
            ? distanceFromTop > dropdownHeight + PADDING_ALLOWANCE
            : distanceFromBottom < dropdownHeight + PADDING_ALLOWANCE &&
              distanceFromTop > dropdownHeight + PADDING_ALLOWANCE;

          updateDropdownAttributes();
          window.addEventListener('resize', handleResize);
          window.addEventListener('scroll', handleScroll);
          scrollableParent.addEventListener('resize', handleResize);
          scrollableParent.addEventListener('scroll', handleScroll);
        });
      },
      { deep: true },
    );
  };

  return {
    autodetectPosition,
    dropdownTop,
    dropdownBottom,
    dropdownLeft,
    dropdownWidth,
    isDirectedUpwards,
    togglerRect,
    dropdownRect,
  };
};