/**
 * Vanilla scroll-scrubbed video (no GSAP).
 * Pins via CSS sticky; maps scroll progress through spacer to video.currentTime.
 */
export function initScrollScrub() {
  const root = document.querySelector("[data-scroll-scrub]");
  if (!root) return;

  const video = root.querySelector("video");
  const spacer = root.querySelector(".scrub-spacer");
  if (!(video instanceof HTMLVideoElement) || !spacer) return;

  if (window.matchMedia("(prefers-reduced-motion: reduce)").matches) {
    video.removeAttribute("autoplay");
    video.controls = true;
    spacer.style.display = "none";
    return;
  }

  let ready = false;
  let seeking = false;
  let target = 0;

  const onReady = () => {
    ready = true;
    video.pause();
  };

  if (video.readyState >= 2) onReady();
  else video.addEventListener("loadeddata", onReady, { once: true });

  video.addEventListener("seeked", () => {
    seeking = false;
    if (Math.abs(video.currentTime - target) > 0.04) {
      seeking = true;
      video.currentTime = target;
    }
  });

  function update() {
    if (!ready || !video.duration) return;
    const rect = spacer.getBoundingClientRect();
    const total = spacer.offsetHeight - window.innerHeight;
    const scrolled = -rect.top;
    const progress = total > 0 ? Math.min(1, Math.max(0, scrolled / total)) : 0;
    target = progress * video.duration;
    if (!seeking && Math.abs(video.currentTime - target) > 0.04) {
      seeking = true;
      video.currentTime = target;
    }
  }

  window.addEventListener("scroll", update, { passive: true });
  window.addEventListener("resize", update);
  update();
}