スクロール位置の保持

<%# Markup for the scroll-restore (scroll position persistence) demo.
    The behavior shines when the DOM is torn down and rebuilt — exactly what Turbo
    does on navigation. To make that observable without leaving the page, the
    "rebuild" button removes the two scroll regions and re-inserts them (demo.js).
    The left region uses stimeo--scroll-restore (its offset is saved to
    sessionStorage and restored on reconnect); the right one has no controller and
    snaps back to the top, so the difference is obvious. It is behavior only — the
    library sets no ARIA/CSS and never moves focus; the box look is demo.css's. %>
<div class="scroll-restore-demo" data-scroll-restore-demo>
  <p><%= t("components.scroll_restore.demo.hint") %></p>

  <div class="scroll-restore-demo__toolbar">
    <button type="button" class="scroll-restore-demo__rebuild" data-scroll-restore-remount>
      <%= t("components.scroll_restore.demo.rebuild") %>
    </button>
  </div>

  <%# demo.js captures this slot's HTML and swaps it out/in to fire the controller's
      disconnect (save) → connect (restore) cycle, mirroring a Turbo navigation. %>
  <div class="scroll-restore-demo__cols" data-scroll-restore-slot>
    <div class="scroll-restore-demo__col">
      <p class="scroll-restore-demo__label" id="scroll-restore-with-label"><%= t(
        "components.scroll_restore.demo.with_label"
      ) %></p>
      <%# Scrolls, but every child is plain <li> text: without a tab stop the list is
          unreachable by keyboard (WCAG 2.1.1). Named by the label above rather than a new
          string, so the two boxes stay distinguishable to a screen reader. %>
      <div
        class="scroll-restore-demo__box"
        tabindex="0"
        role="region"
        aria-labelledby="scroll-restore-with-label"
        data-controller="stimeo--scroll-restore"
        data-stimeo--scroll-restore-key-value="catalog-demo">
        <ol class="scroll-restore-demo__list">
          <% (1..20).each do |n| %>
            <li class="scroll-restore-demo__row"><%= t(
              "components.scroll_restore.demo.row", number: n
            ) %></li>
          <% end %>
        </ol>
      </div>
    </div>

    <div class="scroll-restore-demo__col">
      <p class="scroll-restore-demo__label" id="scroll-restore-without-label"><%= t(
        "components.scroll_restore.demo.without_label"
      ) %></p>
      <div
        class="scroll-restore-demo__box"
        tabindex="0"
        role="region"
        aria-labelledby="scroll-restore-without-label">
        <ol class="scroll-restore-demo__list">
          <% (1..20).each do |n| %>
            <li class="scroll-restore-demo__row"><%= t(
              "components.scroll_restore.demo.row", number: n
            ) %></li>
          <% end %>
        </ol>
      </div>
    </div>
  </div>
</div>

/* Presentation CSS for scroll-restore. The library only saves/restores each box's
   scroll offset (sessionStorage); the toolbar, columns, and list look live here. */
.scroll-restore-demo {
  color: var(--color-text-muted);
}

.scroll-restore-demo__toolbar {
  margin: 0.75rem 0;
}

.scroll-restore-demo__rebuild {
  padding: 0.45rem 0.9rem;
  font: inherit;
  cursor: pointer;
  border: 1px solid var(--border-interactive);
  border-radius: 0.375rem;
  background: var(--surface-card);
  /* Without this the button inherits the UA default black, which lands at 1.24:1
     on the dark card. */
  color: var(--fg);
}

.scroll-restore-demo__rebuild:hover {
  background: var(--surface-subtle);
}

.scroll-restore-demo__rebuild:focus-visible {
  outline: 2px solid var(--color-primary-hover);
  outline-offset: 2px;
}

.scroll-restore-demo__cols {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
}

.scroll-restore-demo__col {
  flex: 1 1 12rem;
  min-width: 0;
}

.scroll-restore-demo__label {
  margin: 0 0 0.35rem;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-text);
}

.scroll-restore-demo__box {
  height: 11rem;
  overflow-y: auto;
  border: 1px solid var(--border-strong);
  border-radius: 0.5rem;
  background: var(--surface-card);
}

.scroll-restore-demo__list {
  margin: 0;
  padding: 0;
  list-style: none;
}

.scroll-restore-demo__row {
  padding: 0.6rem 1rem;
  border-bottom: 1px solid var(--border-default);
}

.scroll-restore-demo__row:last-child {
  border-bottom: none;
}

// Scroll Restore demo driver.
//
// The library's value — keeping an inner scroll region's position when the DOM is
// rebuilt — is otherwise only visible by navigating away and back (or reloading).
// To make it operable in place, the "rebuild" button tears the two scroll regions
// out of the DOM and re-inserts them, which fires the controller's disconnect
// (save) → connect (restore) cycle, mirroring exactly what Turbo does on a visit.
// The left region (stimeo--scroll-restore) returns to its offset; the plain right
// region snaps back to the top.
const stage = document.querySelector("[data-scroll-restore-demo]");

if (stage) {
  const slot = stage.querySelector("[data-scroll-restore-slot]");
  const rebuild = stage.querySelector("[data-scroll-restore-remount]");
  // Snapshot the initial markup so we can re-insert identical regions.
  const template = slot.innerHTML;

  rebuild.addEventListener("click", () => {
    // Remove the regions → Stimulus disconnect (the controller flushes its offset).
    slot.innerHTML = "";
    // Re-insert on the next frame so the removal (disconnect) is processed before
    // the insertion (connect); a synchronous swap could be coalesced into one
    // mutation batch, leaving the save/restore ordering ambiguous.
    requestAnimationFrame(() => {
      slot.innerHTML = template;
    });
  });
}