/* textbook-deeplink.js
   Injected by the server into every /textbook/<slug> page.

   Makes deep links like  /textbook/<slug>#sec-p13  (and #p13) actually open § 13.
   The static algebra/geometry pages ignore location.hash in their own init()
   (they always show §1), and textbook-tracker.js only matches the bare "#pN"
   form via .para-pill — so exam-prep's "#sec-pN" links never navigated.

   This helper is page-agnostic: it activates the target section by clicking the
   matching paragraph card/pill, which works on both the static pages
   (.psel-card[data-id]) and the math6-engine pages (.psel-card / .para-pill),
   falling back to goTo()/scrollIntoView. Idempotent; safe alongside
   textbook-tracker.js (a repeated activation of the same § is a no-op). */
(function () {
  'use strict';

  // "#sec-p13" | "#p13" -> "p13"  (null if not a paragraph anchor)
  function targetId() {
    var h = (location.hash || '').replace(/^#/, '');
    if (!h) return null;
    var m = h.match(/^sec-(p\d+)$/) || h.match(/^(p\d+)$/);
    return m ? m[1] : null;
  }

  function go() {
    var id = targetId();
    if (!id) return;
    var card = document.querySelector('.psel-card[data-id="' + id + '"]');
    if (card) { card.click(); return; }
    var pill = document.querySelector('.para-pill[data-para="' + id + '"]');
    if (pill) { pill.click(); return; }
    if (typeof window.goTo === 'function') { try { window.goTo(id); return; } catch (e) {} }
    var el = document.getElementById('sec-' + id) || document.getElementById(id);
    if (el && el.scrollIntoView) el.scrollIntoView({ behavior: 'smooth', block: 'start' });
  }

  // The page's own init builds the cards/sections on DOMContentLoaded; run after
  // it (microtask + a slower pass for engine-rendered math5/6 pages).
  function boot() {
    setTimeout(go, 60);
    setTimeout(go, 350);
  }

  if (document.readyState === 'loading') {
    document.addEventListener('DOMContentLoaded', boot);
  } else {
    boot();
  }
  window.addEventListener('hashchange', go);
})();