brackt/app/hooks/useFocusTrap.ts

import { useEffect, type RefObject } from "react";

const FOCUSABLE_SELECTOR =
  'button:not([disabled]), [href], input:not([disabled]), select:not([disabled]), textarea:not([disabled]), [tabindex]:not([tabindex="-1"])';

export function useFocusTrap(ref: RefObject<HTMLElement | null>, active: boolean) {
  useEffect(() => {
    if (!active) return;
    const el = ref.current;
    if (!el) return;

    const first = el.querySelector<HTMLElement>(FOCUSABLE_SELECTOR) ?? el;
    first.focus();

    function onKeyDown(e: KeyboardEvent) {
      if (e.key !== "Tab") return;
      const focusables = Array.from(el!.querySelectorAll<HTMLElement>(FOCUSABLE_SELECTOR));
      if (focusables.length === 0) return;
      const firstEl = focusables[0];
      const lastEl = focusables[focusables.length - 1];
      if (e.shiftKey) {
        if (document.activeElement === firstEl) { e.preventDefault(); lastEl.focus(); }
      } else {
        if (document.activeElement === lastEl) { e.preventDefault(); firstEl.focus(); }
      }
    }

    document.addEventListener("keydown", onKeyDown);
    return () => document.removeEventListener("keydown", onKeyDown);
  }, [ref, active]);
}