character-ref/src/components/slider.webc

<script>
  const slider = document.querySelector('.slider');
  const track = slider.querySelector('.track');
  const items = Array.from(slider.querySelectorAll('.track > *'));
  const nav = slider.querySelector('.slider-nav');
  const prevButton = slider.querySelector('button.prev');
  const nextButton = slider.querySelector('button.next');

  const TOLERANCE = 2;

  const debounce = (fn, delay = 300) => {
    let timer;
    return function (...args) {
      clearTimeout(timer);
      timer = setTimeout(() => fn.apply(fn, args), delay);
    };
  };

  const isAtStart = () => Math.floor(track.scrollLeft) <= TOLERANCE;
  const isAtEnd = () =>
    Math.abs(track.scrollLeft + track.offsetWidth - track.scrollWidth) <= TOLERANCE;

  const updateAriaCurrent = (element, index) => {
    currentIndex === index
      ? element.setAttribute('aria-current', 'true')
      : element.removeAttribute('aria-current');
  };

  const updateActiveStates = () => {
    items.forEach(updateAriaCurrent);
    nav?.querySelectorAll('.indicator-btn').forEach(updateAriaCurrent);
    prevButton.disabled = isAtStart();
    nextButton.disabled = isAtEnd();
  };

  let currentIndex = 0;

  const scrollToIndex = (index) => {
    if (index < 0 || index >= items.length || index === currentIndex) return;

    currentIndex = index;
    items[index].scrollIntoView({ behavior: 'smooth', block: 'nearest', inline: 'center' });

    updateActiveStates();
  };

  const prev = () => scrollToIndex(currentIndex - 1);
  const next = () => scrollToIndex(currentIndex + 1);

  const resizeObserver = new ResizeObserver(() => debounce(scrollToIndex(currentIndex)));
  resizeObserver.observe(track);

  const sliderObserver = new IntersectionObserver(
    (entries) => {
      entries.forEach((entry) => {
        if (entry.isIntersecting && entry.intersectionRatio >= 0.75) {
          const index = items.indexOf(entry.target);
          if (index !== -1) {
            currentIndex = index;
            updateActiveStates();
          }
        }
      });
    },
    { root: track, threshold: 0.75, rootMargin: '0px' }
  );

  const initializeGallery = () => {
    items.forEach((el, i) => {
      const btn = document.createElement('button');

      if (i === 0) btn.setAttribute('aria-current', 'true');
      btn.classList.add('indicator-btn');
      btn.dataset.index = i;
      btn.innerText = i + 1;
      btn.setAttribute('aria-label', `Go to item ${i + 1} of ${items.length}`);
      btn.addEventListener('click', () => scrollToIndex(Number(btn.dataset.index)));

      if (i === 0) el.setAttribute('aria-current', 'true');
      el.setAttribute('aria-label', `Item ${i + 1} of ${items.length}`);
      el.setAttribute('tabindex', '0');
      el.setAttribute('role', 'group');

      nav?.appendChild(btn);
    });

    updateActiveStates();
  };

  items.forEach((el) => sliderObserver.observe(el));
  prevButton.addEventListener('click', prev);
  nextButton.addEventListener('click', next);
  track.addEventListener('scroll', debounce(updateActiveStates, 100));
  document.addEventListener('DOMContentLoaded', initializeGallery);
</script>

<section aria-label="Slider" webc:root="override">
  <button class="prev" aria-label="Previous item">
    <icon icon="fa6-solid:chevron-left"></icon>
  </button>
  <button class="next" aria-label="Next item">
    <icon icon="fa6-solid:chevron-right"></icon>
  </button>

  <div class="track">
    <slot></slot>
  </div>

  <nav webc:if="nav !== false" class="slider-nav" aria-label="Slider"></nav>
</section>

<style webc:scoped="slider">
  :host {
    display: grid;
    grid-auto-columns: auto 1fr auto;
    grid-template-areas:
      'prev track next'
      '. progress .';
    align-items: center;
    gap: 1em;
    margin-block: var(--inbox-spacing);
  }

  :host :where(.prev, .next, .indicator-btn) {
    --gradient-dir: to bottom right;
    --gradient-start: var(--clr-box-gradient-start);
    --gradient-end: var(--clr-box-gradient-end);

    position: relative;

    font-size: 1.25em;
    color: var(--clr-text);
    cursor: pointer;

    background: linear-gradient(
      var(--gradient-dir),
      var(--gradient-start) 0%,
      var(--gradient-end) 50%
    );

    box-shadow: 0.125em 0.125em 0.5em var(--clr-box-shadow);

    border: none;
    border-radius: 100%;
    padding: 0.875em;

    z-index: 1;
  }

  :host :where(.prev, .next, .indicator-btn):active::after {
    --gradient-dir: to top left;
  }

  :host :where(.prev, .next, .indicator-btn)::after {
    --gradient-dir: to bottom right;
    --gradient-start: var(--clr-quick-info-gradient-start);
    --gradient-end: var(--clr-quick-info-gradient-end);

    content: '';
    position: absolute;
    inset: var(--border-thin);
    background: linear-gradient(
      var(--gradient-dir),
      var(--gradient-start) 0%,
      var(--gradient-end) 50%
    );
    border-radius: inherit;
    z-index: -1;
  }

  :host :where(.prev, .next) {
    --btn-alignment: 0.25em;
    grid-row: track;

    @media (min-width: 40em) {
      --btn-alignment: calc(var(--inbox-spacing) + 1rem);
    }
  }

  :host :where(.prev, .next):disabled {
    cursor: not-allowed;
    opacity: 0.5;
  }

  :host :where(.prev, .next) svg {
    position: absolute;
    inset: 0;
    padding: 0.375em;
  }

  :host .prev {
    grid-column: prev;
    left: var(--btn-alignment);
  }

  :host .next {
    grid-column: next;
    right: var(--btn-alignment);
  }

  :host .track {
    grid-row: track;
    grid-column: prev / next;
    display: grid;
    grid-auto-flow: column;
    grid-auto-columns: 100%;
    gap: 2em;

    border-radius: 1em;

    overflow-x: auto;
    scroll-snap-type: x mandatory;
    scroll-behavior: smooth;
    scrollbar-width: none;
  }

  :host .track > * {
    scroll-snap-align: center;
    padding-inline: var(--inbox-spacing);
  }

  :host .track::-webkit-scrollbar {
    display: none;
  }

  :host .ref-image :first-child {
    grid-row: image / caption;
  }

  :host .ref-image img {
    width: 100%;
    height: 80vw;
    object-fit: cover;
  }

  :host .ref-image .caption {
    font-size: 0.875em;
    text-wrap: balance;

    background: oklch(from var(--clr-box-background) l c h / 0.75);

    padding-block: 0.5em;
    padding-inline: 1em;
  }

  :host .slider-nav {
    --indicator-size: 2.5em;

    grid-row: progress;
    grid-column: prev / next;

    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(min(1em, 100%), var(--indicator-size)));
    gap: 0.5em;
    place-content: center;
    place-items: center;
    font-size: 0.875em;

    padding-inline: var(--inbox-spacing);
  }

  :host .indicator-btn {
    font-size: 1em;
    width: var(--indicator-size);
    height: var(--indicator-size);
    padding: 0;
    aspect-ratio: 1 / 1;
  }

  :host .indicator-btn[aria-current='true']::after {
    --gradient-dir: to top left;
  }
</style>