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

/**
 * "Peek open on hover or keyboard focus" for a floating panel — the shared brain behind the side
 * panels, which sit slim until you point at them or tab into them.
 *
 * Returns `active` plus THREE handler groups so a consumer can scope hover and focus independently:
 *   - `hoverHandlers` — pointer enter/leave, with a short GRACE period on leave so the pointer can
 *     cross a gap between two separate peek regions (e.g. the docked tab and the expanded card, which
 *     are separate absolutely-positioned elements) without the panel collapsing mid-move. Put these on
 *     ONLY the visible affordances (the tab handle + the card), so approaching empty gutter next to the
 *     panel does not pop it open.
 *   - `focusHandlers` — focus/blur, tracked through the REACT tree so a portaled child menu still
 *     counts as "inside". Put these on the outer container so keyboard focus anywhere within holds it.
 *   - `handlers` — both groups merged, for the simple single-element case.
 *
 * The one focus case that misses: a portaled menu unmounts while focused — browsers fire NO blur when
 * a focused node is removed, so focus silently falls to the body and would latch `focused` on forever.
 * Hence the document-level safety net: when focus has landed nowhere, clear it.
 */
export function useHoverFocusWithin() {
  const [hovered, setHovered] = useState(false);
  const [focused, setFocused] = useState(false);
  const leaveTimer = useRef<ReturnType<typeof setTimeout> | undefined>(undefined);

  const enter = useCallback(() => {
    clearTimeout(leaveTimer.current);
    setHovered(true);
  }, []);
  const leaveSoon = useCallback(() => {
    clearTimeout(leaveTimer.current);
    leaveTimer.current = setTimeout(() => setHovered(false), 120);
  }, []);
  useEffect(() => () => clearTimeout(leaveTimer.current), []);

  useEffect(() => {
    let timer: number | undefined;
    const clearIfFocusLandedNowhere = () => {
      const el = document.activeElement;
      if (!el || el === document.body || el === document.documentElement) setFocused(false);
    };
    // Deferred a tick so activeElement has settled, and rescheduled rather than queued — only the
    // latest state matters.
    const soon = () => {
      window.clearTimeout(timer);
      timer = window.setTimeout(clearIfFocusLandedNowhere, 0);
    };
    document.addEventListener("focusout", soon);
    document.addEventListener("click", soon);
    return () => {
      document.removeEventListener("focusout", soon);
      document.removeEventListener("click", soon);
      window.clearTimeout(timer);
    };
  }, []);

  const hoverHandlers = { onMouseEnter: enter, onMouseLeave: leaveSoon };
  const focusHandlers = {
    onFocus: () => setFocused(true),
    onBlur: (e: FocusEvent) => {
      const to = e.relatedTarget as Element | null;
      if (e.currentTarget.contains(to)) return;
      // A dialog opened FROM inside the panel (the rail row's "Delete?" confirm) renders at the app
      // root, so neither the DOM nor the React tree sees it as inside — and collapsing the panel under
      // it unmounted the very row the dialog hands the focus back to, leaving a keyboard user on
      // <body> after Cancel (measured in Chrome, E11 S2). Hold while the focus is in a dialog: when it
      // closes, the focus either comes back in here (onFocus) or lands nowhere, which the
      // document-level net below clears.
      if (to?.closest('[aria-modal="true"]')) return;
      setFocused(false);
    },
  };

  return {
    active: hovered || focused,
    hoverHandlers,
    focusHandlers,
    handlers: { ...hoverHandlers, ...focusHandlers },
  };
}