'use strict';
/**
 * REVEAL (D1-finish, 2026-07-31) — IntersectionObserver row reveal + rail highlight,
 * per `Vyndr System.dc.html`.
 *
 * Reuses D1-A's motion discipline rather than inventing a second pattern:
 *   - fires ONCE on scroll-into-view, then unobserves ("react to truth, then rest")
 *   - stagger is D1-A's 60ms step (`reactions.bootDelayMs`) — one source of truth
 *   - reduced-motion is honoured by the CSS (`.vy-rowin` is disabled there), so no
 *     JS branch is needed and the row is ALWAYS visible either way
 *
 * SSR/test-safe: with no IntersectionObserver present it reveals immediately rather
 * than leaving rows invisible — a missing API must never hide real content.
 */
const { bootDelayMs } = require('./reactions');

function supported() {
  return typeof window !== 'undefined' && typeof window.IntersectionObserver === 'function';
}

/**
 * observeRows(nodes, onReveal) — reveal each node once when it enters view.
 * Returns a disconnect function. `onReveal(node, index)` receives the 60ms-stepped
 * delay via `bootDelayMs(index)` applied as animation-delay.
 */
function observeRows(nodes, onReveal) {
  const list = Array.from(nodes || []);
  const fire = (node, i) => {
    if (!node || node.dataset && node.dataset.revealed === '1') return;
    if (node.dataset) node.dataset.revealed = '1';
    if (node.style) node.style.animationDelay = `${bootDelayMs(i)}ms`;
    if (node.classList) node.classList.add('vy-rowin');
    if (typeof onReveal === 'function') onReveal(node, i);
  };
  if (!supported()) { list.forEach(fire); return () => {}; }
  const idx = new Map(list.map((n, i) => [n, i]));
  const io = new window.IntersectionObserver((entries) => {
    for (const e of entries) {
      if (!e.isIntersecting) continue;
      fire(e.target, idx.get(e.target) || 0);
      io.unobserve(e.target);          // ONCE — never a loop
    }
  }, { rootMargin: '0px 0px -10% 0px', threshold: 0.15 });
  list.forEach((n) => n && io.observe(n));
  return () => io.disconnect();
}

module.exports = { observeRows, supported };