// Hover (and keyboard-focus) tooltips for the whole app, without touching every button:
//  - anything with data-tip="…" shows that text (used for shortcut hints like "Search (/)")
//  - anything with title="…" shows it too, in the app's style and without the browser's long delay
//  - an icon-only button (no visible words) shows its aria-label
// Touch screens have no hover, so nothing appears there.
import { useEffect, useRef, useState } from 'react';
import { themeVars } from './reader/readerThemes.js';

const SHOW_DELAY = 450;
const SELECTOR = '[data-tip], [title], button[aria-label], a[aria-label], [role="button"][aria-label], [role="tab"][aria-label]';

const canHover = () => (typeof window.matchMedia === 'function' ? window.matchMedia('(hover: hover)').matches : true);

// The words a tooltip should show for an element, or '' for none. A title is moved to data-tip the first
// time (so the browser's own tooltip doesn't also appear); a title on a button with no other name becomes
// its aria-label so screen readers keep it.
export function tipFor(el) {
  if (!(el instanceof HTMLElement)) return '';
  if (el.hasAttribute('title')) {
    const title = el.getAttribute('title').trim();
    if (title) {
      if (!el.getAttribute('aria-label') && el.textContent.replace(/\s+/g, '').length <= 2) el.setAttribute('aria-label', title);
      if (!el.hasAttribute('data-tip')) el.setAttribute('data-tip', title);
    }
    el.removeAttribute('title');
  }
  const tip = el.getAttribute('data-tip');
  if (tip) return tip;
  // Icon-only controls (little or no text of their own) explain themselves with their label
  const label = el.getAttribute('aria-label');
  const visible = el.textContent.replace(/\s+/g, '').length;
  return label && visible <= 2 ? label : '';
}

export default function Tooltips({ theme }) {
  const [tip, setTip] = useState(null); // { text, x, y, below }
  const timer = useRef(null);
  const current = useRef(null);
  const box = useRef(null);

  useEffect(() => {
    const hide = () => {
      window.clearTimeout(timer.current);
      if (current.current) current.current.removeAttribute('aria-describedby');
      current.current = null;
      setTip(null);
    };
    const show = (el, text) => {
      const r = el.getBoundingClientRect();
      current.current = el;
      el.setAttribute('aria-describedby', 'app-tooltip');
      setTip({ text, x: r.left + r.width / 2, y: r.top, bottom: r.bottom });
    };
    const find = (node) => (node instanceof Element ? node.closest(SELECTOR) : null);

    const onOver = (e) => {
      if (!canHover()) return;
      const el = find(e.target);
      if (!el || el === current.current) return;
      hide();
      const text = tipFor(el);
      if (!text || el.disabled) return;
      timer.current = window.setTimeout(() => show(el, text), SHOW_DELAY);
    };
    const onOut = (e) => {
      const el = find(e.target);
      if (!el || (e.relatedTarget instanceof Node && el.contains(e.relatedTarget))) return;
      hide();
    };
    const onFocus = (e) => {
      const el = find(e.target);
      if (!el || !el.matches(':focus-visible')) return; // only keyboard focus, not a mouse click
      const text = tipFor(el);
      if (text) { window.clearTimeout(timer.current); show(el, text); }
    };
    const onKey = (e) => { if (e.key === 'Escape') hide(); };

    document.addEventListener('pointerover', onOver);
    document.addEventListener('pointerout', onOut);
    document.addEventListener('pointerdown', hide, true);
    document.addEventListener('focusin', onFocus);
    document.addEventListener('focusout', hide);
    document.addEventListener('keydown', onKey);
    window.addEventListener('scroll', hide, true);
    window.addEventListener('resize', hide);
    return () => {
      window.clearTimeout(timer.current);
      document.removeEventListener('pointerover', onOver);
      document.removeEventListener('pointerout', onOut);
      document.removeEventListener('pointerdown', hide, true);
      document.removeEventListener('focusin', onFocus);
      document.removeEventListener('focusout', hide);
      document.removeEventListener('keydown', onKey);
      window.removeEventListener('scroll', hide, true);
      window.removeEventListener('resize', hide);
    };
  }, []);

  if (!tip) return null;
  // Centred over the control, kept inside the window, and flipped below it when there's no room above
  const width = box.current?.offsetWidth ?? 0;
  const left = Math.max(8, Math.min(tip.x - width / 2, window.innerWidth - width - 8));
  const flip = tip.y < 40;
  return (
    <div
      ref={box} id="app-tooltip" role="tooltip" style={{ ...themeVars(theme), left, top: flip ? tip.bottom + 8 : tip.y - 8, transform: flip ? 'none' : 'translateY(-100%)' }}
      className="pointer-events-none fixed z-[120] max-w-[16rem] rounded-lg bg-[var(--r-text)] px-2.5 py-1.5 font-sans text-xs leading-snug text-[var(--r-bg)] shadow-lg"
    >
      {tip.text}
    </div>
  );
}