楽観的 UI

<%# optimistic: wraps a real Turbo form POST. On turbo:submit-start the hidden
    "Liked" face shows and the "Like" face hides IMMEDIATELY (each toggled
    target is marked); on success the toggle is kept (commit — the final DOM
    belongs to the server's Turbo Stream response, which updates the status
    line below), on failure exactly the marked toggles are rolled back. The
    second form posts fail=1, which the demo endpoint rejects with 422, so you
    can watch the rollback. The hidden authenticity_token is Rails' CSRF token
    (form_with renders it automatically in a real app). %>
<div class="optimistic-demo">
  <p class="optimistic-demo__hint"><%= t("components.optimistic.demo.hint") %></p>
  <div class="optimistic-demo__row">
    <form class="optimistic-demo__form" method="post"
          action="<%= optimistic_demo_likes_path %>"
          data-controller="stimeo--optimistic">
      <%= hidden_field_tag :authenticity_token, form_authenticity_token, id: nil %>
      <button type="submit" class="demo-trigger optimistic-demo__button">
        <span class="optimistic-demo__face" data-stimeo--optimistic-target="hide">
          <svg class="demo-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor"
               stroke-width="2" stroke-linecap="round" stroke-linejoin="round"
               aria-hidden="true">
            <path d="M19 14c1.5-1.5 3-3.2 3-5.5A5.5 5.5 0 0 0 16.5 3c-1.8 0-3 .5-4.5 2
                     -1.5-1.5-2.7-2-4.5-2A5.5 5.5 0 0 0 2 8.5c0 2.3 1.5 4 3 5.5l7 7Z"/>
          </svg>
          <%= t("components.optimistic.demo.like") %>
        </span>
        <span class="optimistic-demo__face" hidden data-stimeo--optimistic-target="show">
          <svg class="demo-icon" viewBox="0 0 24 24" fill="currentColor" stroke="none"
               aria-hidden="true">
            <path d="M19 14c1.5-1.5 3-3.2 3-5.5A5.5 5.5 0 0 0 16.5 3c-1.8 0-3 .5-4.5 2
                     -1.5-1.5-2.7-2-4.5-2A5.5 5.5 0 0 0 2 8.5c0 2.3 1.5 4 3 5.5l7 7Z"/>
          </svg>
          <%= t("components.optimistic.demo.liked") %>
        </span>
      </button>
    </form>

    <%# Same wiring, but the server rejects it (fail=1 → 422): the optimistic
        toggle appears for the request's duration, then rolls back. %>
    <form class="optimistic-demo__form" method="post"
          action="<%= optimistic_demo_likes_path %>"
          data-controller="stimeo--optimistic">
      <%= hidden_field_tag :authenticity_token, form_authenticity_token, id: nil %>
      <input type="hidden" name="fail" value="1">
      <button type="submit" class="demo-trigger optimistic-demo__button">
        <span class="optimistic-demo__face" data-stimeo--optimistic-target="hide">
          <svg class="demo-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor"
               stroke-width="2" stroke-linecap="round" stroke-linejoin="round"
               aria-hidden="true">
            <path d="M19 14c1.5-1.5 3-3.2 3-5.5A5.5 5.5 0 0 0 16.5 3c-1.8 0-3 .5-4.5 2
                     -1.5-1.5-2.7-2-4.5-2A5.5 5.5 0 0 0 2 8.5c0 2.3 1.5 4 3 5.5l7 7Z"/>
          </svg>
          <%= t("components.optimistic.demo.like_fail") %>
        </span>
        <span class="optimistic-demo__face" hidden data-stimeo--optimistic-target="show">
          <svg class="demo-icon" viewBox="0 0 24 24" fill="currentColor" stroke="none"
               aria-hidden="true">
            <path d="M19 14c1.5-1.5 3-3.2 3-5.5A5.5 5.5 0 0 0 16.5 3c-1.8 0-3 .5-4.5 2
                     -1.5-1.5-2.7-2-4.5-2A5.5 5.5 0 0 0 2 8.5c0 2.3 1.5 4 3 5.5l7 7Z"/>
          </svg>
          <%= t("components.optimistic.demo.liked") %>
        </span>
      </button>
    </form>
  </div>
  <%# The server's Turbo Stream response updates this line (success and 422 alike). %>
  <p id="optimistic-demo-status" class="optimistic-demo__status" role="status"></p>
</div>

/*
 * Presentation-only styles for the optimistic demo. The library toggles the
 * hidden attribute on the show/hide faces and flips data-optimistic/aria-busy
 * on the form; this CSS lays the two forms out and dims the form while a
 * submission is in flight.
 */

.optimistic-demo {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  max-width: 32rem;
}

.optimistic-demo__hint {
  margin: 0;
  font-size: 0.9rem;
  color: var(--muted);
}

.optimistic-demo__row {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
}

/* While the optimistic state is applied (request in flight), dim the form. */
.optimistic-demo__form[data-optimistic="true"] {
  opacity: 0.7;
}

.optimistic-demo__button {
  display: inline-flex;
  align-items: center;
}

.optimistic-demo__face {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
}

.optimistic-demo__face .demo-icon {
  width: 1rem;
  height: 1rem;
}

/* The committed "Liked" face reads in the accent color. */
.optimistic-demo__face[data-stimeo--optimistic-target="show"] {
  color: var(--accent);
}

.optimistic-demo__status {
  margin: 0;
  min-height: 1.25rem;
  font-size: 0.9rem;
  color: var(--muted);
}