ステップインジケータ

<%# Markup for the step-indicator (read-only progress) demo.
    The library holds the current step number, sets data-state on each li, sets
    aria-current="step" on the current li, and updates the progress CSS variable
    (--stimeo--step-indicator-ratio). The steps themselves aren't interactive, so the
    current step is updated via the external step:set event (fired by demo.js from the
    prev/next buttons). %>
<div class="step-indicator-demo">
  <%# --steps lets the CSS put the track between the first and last dot centres:
      the library's ratio is "how far along the range", and the range runs from
      centre to centre, not edge to edge. %>
  <ol
    class="step-indicator"
    style="--steps: 4"
    data-controller="stimeo--step-indicator"
    aria-label="<%= t("components.step_indicator.demo.label") %>"
    data-stimeo--step-indicator-current-value="1"
    data-action="step:set->stimeo--step-indicator#setCurrent">
    <% %w[cart shipping payment confirm].each_with_index do |step, index| %>
      <li
        class="step-indicator__step"
        data-stimeo--step-indicator-target="step"
        <%= "data-state=\"complete\"".html_safe if index < 1 %>
        <%= "data-state=\"current\" aria-current=\"step\"".html_safe if index == 1 %>
        <%= "data-state=\"upcoming\"".html_safe if index > 1 %>>
        <span class="step-indicator__dot"></span>
        <span class="step-indicator__label"><%= t(
          "components.step_indicator.demo.steps.#{step}"
        ) %></span>
      </li>
    <% end %>
  </ol>

  <div class="step-indicator__controls">
    <button type="button" class="demo-trigger" data-step-indicator-prev>
      <%= t("components.step_indicator.demo.back") %>
    </button>
    <button type="button" class="demo-trigger" data-step-indicator-next>
      <%= t("components.step_indicator.demo.advance") %>
    </button>
  </div>
</div>

/*
 * Presentation-only styles for the step-indicator demo.
 * Complete / current / upcoming are built by reacting to each li's data-state. The
 * progress bar uses --stimeo--step-indicator-ratio (0–1, updated by the library) as its width.
 *
 * The ratio measures how far along the *range* the current step is, and the range runs
 * from the first dot's centre to the last one's — so the track is inset by half a step
 * (--steps is the count the template renders), not by half a dot. Insetting by the dot
 * instead leaves the fill short of the first dot and past the last one.
 */

.step-indicator {
  display: flex;
  gap: 0;
  margin: 0;
  padding: 0;
  list-style: none;
  position: relative;
}

.step-indicator::before,
.step-indicator::after {
  content: "";
  position: absolute;
  top: 0.5rem;
  left: calc(100% / var(--steps, 2) / 2);
  right: calc(100% / var(--steps, 2) / 2);
  height: 2px;
  background: var(--surface-subtle);
}

.step-indicator::after {
  right: auto;
  width: calc((100% - 100% / var(--steps, 2)) * var(--stimeo--step-indicator-ratio, 0));
  background: var(--accent, var(--color-primary));
  transition: width 0.2s ease;
}

.step-indicator__step {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.8125rem;
  color: var(--color-text-subtle);
}

.step-indicator__dot {
  position: relative;
  z-index: 1;
  width: 1rem;
  height: 1rem;
  border-radius: 50%;
  background: var(--border-strong);
}

.step-indicator__step[data-state="complete"] .step-indicator__dot,
.step-indicator__step[data-state="current"] .step-indicator__dot {
  background: var(--accent, var(--color-primary));
}

.step-indicator__step[data-state="current"] {
  color: var(--fg, var(--color-text));
  font-weight: 600;
}

.step-indicator__controls {
  display: flex;
  gap: 0.5rem;
  margin-top: 1.25rem;
}

// step-indicator external-update demo (consumer-side JS).
//
// The core controller (stimeo--step-indicator) is read-only: it only holds the current
// step and syncs data-state / aria-current / the progress CSS variable (no interaction).
// Changing the current step is done externally via the step:set event by contract, so
// here the prev/next buttons read the current value and fire step:set with a clamped new index.
document.querySelectorAll('[data-controller~="stimeo--step-indicator"]').forEach((list) => {
  const root = list.closest('.step-indicator-demo') ?? list.parentElement;
  if (!root) return;
  const total = list.querySelectorAll('[data-stimeo--step-indicator-target="step"]').length;

  const attr = 'data-stimeo--step-indicator-current-value';
  const move = (delta) => {
    const current = Number(list.getAttribute(attr) ?? 0);
    const next = Math.min(total - 1, Math.max(0, current + delta));
    list.dispatchEvent(new CustomEvent('step:set', { detail: { current: next } }));
  };

  root.querySelector('[data-step-indicator-prev]')?.addEventListener('click', () => move(-1));
  root.querySelector('[data-step-indicator-next]')?.addEventListener('click', () => move(1));
});