/** Scroll snapping is the baseline; arrows, dots and controllable playback enhance it. */
export function initSliders(doc = document) {
  const view = doc.defaultView;
  const cleanups = [];
  doc.querySelectorAll('.block-slider').forEach(slider => {
    const slides = [...slider.querySelectorAll(':scope > .slider-slide')];
    if (slides.length < 2 || slider.dataset.enhanced) return;
    slider.dataset.enhanced = 'true';
    const events = new view.AbortController(), signal = events.signal;
    const preference = view.matchMedia('(prefers-reduced-motion: reduce)');
    // The browser preference counts only when the website says so (Einstellungen → Bewegung).
    const reduced = () => doc.documentElement.classList.contains('motion-respect') && preference.matches;
    const seconds = Number(slider.dataset.autoplay || 0);
    let playing = seconds >= 3 && !reduced(), hover = false, visible = false, timer;
    const controls = doc.createElement('div'); controls.className = 'slider-controls';
    for (const name of slider.classList) if (name.startsWith('visibility-')) controls.classList.add(name);
    controls.setAttribute('role', 'group'); controls.setAttribute('aria-label', 'Slider bedienen');
    const button = (text, label, action) => {
      const node = doc.createElement('button'); node.type = 'button'; node.textContent = text;
      node.setAttribute('aria-label', label); node.setAttribute('aria-controls', slider.id);
      node.addEventListener('click', event => { event.preventDefault(); event.stopPropagation(); action(); }, { signal });
      controls.append(node); return node;
    };
    const left = slide => slide.getBoundingClientRect().left - slider.getBoundingClientRect().left + slider.scrollLeft;
    const available = () => slides.map((slide, i) => slide.getClientRects().length ? i : -1).filter(i => i >= 0);
    const active = () => {
      let index = 0, distance = Infinity;
      available().forEach(i => { const delta = Math.abs(left(slides[i]) - slider.scrollLeft); if (delta < distance) { distance = delta; index = i; } });
      return index;
    };
    let settle = null;
    const go = index => {
      if (!available().includes(index)) return;
      const target = Math.max(0, Math.min(slider.scrollWidth - slider.clientWidth, left(slides[index])));
      if (reduced()) { slider.scrollTo({ left: target, behavior: 'instant' }); return; }
      // Safari cancels a smooth scroll on a snapping container and snaps back to the slide it
      // came from - the slider stutters instead of moving on. Snapping is switched off for the
      // ride and put back once the movement has settled, on the exact start of a slide, so
      // restoring it moves nothing.
      clearInterval(settle);
      const snap = slider.style.scrollSnapType;
      slider.style.scrollSnapType = 'none';
      slider.scrollTo({ left: target, behavior: 'smooth' });
      // Restored on arrival, or after two seconds if the ride was interrupted - a background tab
      // pauses smooth scrolling, and snapping must not come back halfway.
      let ticks = 0;
      settle = setInterval(() => {
        if (Math.abs(slider.scrollLeft - target) < 1 || ++ticks > 25) { clearInterval(settle); settle = null; slider.style.scrollSnapType = snap; }
      }, 80);
    };
    const step = direction => {
      const visible = available(), position = visible.indexOf(active());
      if (!visible.length) return;
      const last = slider.scrollLeft + slider.clientWidth >= slider.scrollWidth - 2;
      const first = slider.scrollLeft <= 2;
      go(direction > 0 ? (last ? visible[0] : visible[Math.min(visible.length - 1, position + 1)]) : (first ? visible.at(-1) : visible[Math.max(0, position - 1)]));
    };
    const manual = action => { playing = false; clearTimeout(timer); update(); action(); };
    const previous = button('←', 'Vorherige Folie', () => manual(() => step(-1))); previous.className = 'slider-prev';
    const count = doc.createElement('span'); count.className = 'slider-position'; controls.append(count);
    const next = button('→', 'Nächste Folie', () => manual(() => step(1))); next.className = 'slider-next';
    const dots = [];
    if (slider.classList.contains('slider-dots')) {
      const group = doc.createElement('div'); group.className = 'slider-control-dots'; controls.append(group);
      slides.forEach((slide, i) => {
        const dot = button('●', `Folie ${i + 1} anzeigen`, () => manual(() => go(i))); group.append(dot); dots.push(dot);
      });
    }
    const play = seconds >= 3 ? button('', 'Automatische Wiedergabe pausieren', () => { playing = !playing; update(); schedule(); }) : null;
    if (play) play.className = 'slider-play';
    const update = () => {
      const visible = available();
      const fits = visible.length < 2 || slider.scrollWidth <= slider.clientWidth + 2;
      controls.hidden = fits; previous.disabled = next.disabled = fits;
      const index = active(); count.textContent = `${Math.max(0, visible.indexOf(index) + 1)} / ${visible.length}`;
      dots.forEach((dot, i) => { dot.hidden = !visible.includes(i); dot.setAttribute('aria-pressed', String(i === index)); });
      if (play) {
        play.textContent = playing ? 'Pause' : 'Wiedergabe'; play.dataset.playing = String(playing);
        // Der zugängliche Name beginnt mit dem sichtbaren Text (WCAG 2.5.3): wer „Pause“ liest, kann „Pause“ sagen.
        play.setAttribute('aria-label', playing ? 'Pause: automatische Wiedergabe anhalten' : 'Wiedergabe: automatisch weiterblättern');
        play.disabled = reduced(); play.title = reduced() ? 'Automatik ist bei reduzierter Bewegung deaktiviert.' : '';
      }
    };
    const schedule = () => {
      clearTimeout(timer);
      if (playing && !reduced()) timer = setTimeout(() => { if (playing && !hover && visible && !doc.hidden) step(1); schedule(); }, seconds * 1000);
    };
    const pause = () => { playing = false; update(); clearTimeout(timer); };
    // Slider and controls share a positioned shell, so arrows and dots can lie on the picture
    // the way the Kant-IT hero slider draws them.
    const shell = doc.createElement('div'); shell.className = 'slider-shell';
    slider.replaceWith(shell); shell.append(slider, controls);
    slider.classList.add('slider-controlled'); update();
    slider.addEventListener('scroll', update, { passive: true, signal });
    view.addEventListener('resize', update, { passive: true, signal });
    slider.addEventListener('pointerenter', () => { hover = true; }, { signal });
    slider.addEventListener('pointerleave', () => { hover = false; schedule(); }, { signal });
    for (const event of ['pointerdown', 'wheel', 'touchstart', 'focusin']) slider.addEventListener(event, pause, { passive: true, signal });
    slider.addEventListener('keydown', event => {
      if (event.target !== slider || !['ArrowLeft', 'ArrowRight'].includes(event.key)) return;
      event.preventDefault(); manual(() => step(event.key === 'ArrowRight' ? 1 : -1));
    }, { signal });
    const observer = new view.IntersectionObserver(entries => { visible = entries[0].isIntersecting; }, { threshold: 0 }); observer.observe(slider);
    const resize = new view.ResizeObserver(update); resize.observe(slider);
    preference.addEventListener('change', () => { if (reduced()) pause(); update(); }, { signal });
    schedule();
    cleanups.push(() => { clearTimeout(timer); clearInterval(settle); slider.style.scrollSnapType = ''; events.abort(); observer.disconnect(); resize.disconnect(); controls.remove(); shell.replaceWith(slider); slider.classList.remove('slider-controlled'); delete slider.dataset.enhanced; });
  });
  return () => cleanups.forEach(cleanup => cleanup());
}

if (!document.querySelector('#editor')) initSliders();