App Bar

Cần header cho mobile screen?
├─ Screen title + back button → App Bar
│   ├─ Fixed trên hero image → variant="transparent"
│   ├─ Medium title + subtitle → variant="medium"
│   ├─ Large title collapse on scroll → variant="large"
│   ├─ Standard solid background → variant="default"
│   ├─ Glass/translucent → variant="glass"
│   └─ Search-focused → variant="search"
│   (Small / Medium có thể showTitle={false} khi context đủ rõ)
├─ Web desktop navigation → navigation-menu
├─ No title, just actions → Toolbar
└─ In-flow section heading → Typography heading

<!-- HTML skeleton with data-slot -->
<header class="ground-appbar" data-slot="app-bar" role="banner">
  <div class="ground-appbar__leading" data-slot="app-bar-leading">
    <button aria-label="Go back">←</button>
  </div>
  <h1 class="ground-appbar__title" data-slot="app-bar-title">Title</h1>
  <div class="ground-appbar__actions" data-slot="app-bar-actions">
    <button aria-label="More">⋯</button>
  </div>
</header>

interface AppBarProps {
  /** Visual variant */
  variant?: 'default' | 'medium' | 'transparent' | 'glass' | 'large' | 'search';
  /** Screen title */
  title: string;
  /** Show/hide title — default: true. Set false for map, media, camera screens */
  showTitle?: boolean;
  /** Subtitle (medium, large variants) */
  subtitle?: string;
  /** Show back button */
  showBack?: boolean;
  /** Back button label (iOS style — default: hidden) */
  backLabel?: string;
  /** Back handler */
  onBack?: () => void;
  /** Action buttons (max 3) */
  actions?: AppBarAction[];
  /** Add shadow on scroll */
  elevateOnScroll?: boolean;
  /** Collapse large title on scroll */
  collapseOnScroll?: boolean;
}

interface AppBarAction {
  /** Icon element */
  icon: ReactNode;
  /** Accessible label */
  label: string;
  /** Click handler */
  onClick: () => void;
  /** Badge count */
  badge?: number;
}

{/* Default app bar */}
<AppBar
  variant="default"
  title="Flight"
  showBack
  onBack={() => router.back()}
  actions={[
    { icon: <MoreIcon />, label: "More options", onClick: openMenu }
  ]}
  elevateOnScroll
/>

{/* Transparent over hero */}
<AppBar
  variant="transparent"
  title="Sydney"
  showBack={false}
  actions={[
    { icon: <BellIcon />, label: "Notifications", onClick: openNotifs, badge: 2 },
    { icon: <ProfileIcon />, label: "Profile", onClick: openProfile }
  ]}
/>

{/* Large title (iOS/OneUI style) */}
<AppBar
  variant="large"
  title="Boarding Pass"
  showBack
  onBack={goBack}
  collapseOnScroll
/>

{/* Glass (Liquid Glass) */}
<AppBar
  variant="glass"
  title="Search"
  actions={actions}
/>

/* Container — Ground layer */
.ground-appbar {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: var(--z-index-fixed);
  background: var(--background);
  padding-top: env(safe-area-inset-top, var(--spacing-11));
  transition: box-shadow var(--duration-normal-1) var(--easing-standard);
}

/* Scrolled — shadow appears */
.ground-appbar--scrolled {
  box-shadow: var(--shadow-sm);
}

/* Inner layout */
.ground-appbar__inner {
  display: flex;
  align-items: center;
  height: var(--spacing-11); /* 44px compact */
  padding: 0 var(--spacing-4);
  gap: var(--spacing-2);
}

/* Back button */
.ground-appbar__back {
  width: var(--size-min-width-11); /* 44px touch */
  height: var(--size-min-width-11);
  border-radius: var(--radius-full);
  background: none;
  border: none;
  color: var(--foreground);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  margin-left: calc(-1 * var(--spacing-2));
  transition: background var(--duration-fast-2) var(--easing-standard);
}

.ground-appbar__back:hover {
  background: var(--state-layer-hover);
}

/* Title */
.ground-appbar__title {
  flex: 1;
  font-size: var(--font-size-lg);
  font-weight: var(--font-weight-semibold);
  letter-spacing: var(--font-tracking-snug);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  text-align: center;
  color: var(--foreground);
}

/* Actions */
.ground-appbar__actions {
  display: flex;
  align-items: center;
  gap: var(--spacing-0-5);
}

.ground-appbar__action {
  width: var(--size-min-width-11);
  height: var(--size-min-width-11);
  border-radius: var(--radius-full);
  background: none;
  border: none;
  color: var(--foreground);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  position: relative;
  transition: background var(--duration-fast-2) var(--easing-standard);
}

.ground-appbar__action:hover {
  background: var(--state-layer-hover);
}

/* ─── Transparent variant ─── */
.ground-appbar--transparent {
  background: transparent;
  color: var(--foreground-inverse, #fff);
}

.ground-appbar--transparent .ground-appbar__title,
.ground-appbar--transparent .ground-appbar__back,
.ground-appbar--transparent .ground-appbar__action {
  color: var(--foreground-inverse, #fff);
  text-shadow: 0 1px 4px rgba(0, 0, 0, 0.3);
}

/* ─── Medium flexible variant ─── */
.ground-appbar--medium {
  /* Taller container for medium flexible */
}

.ground-appbar--medium .ground-appbar__inner {
  height: auto;
  flex-direction: column;
  align-items: flex-start;
  padding: var(--spacing-3) var(--spacing-4);
}

.ground-appbar--medium .ground-appbar__row {
  display: flex;
  align-items: center;
  width: 100%;
  height: var(--spacing-11); /* 44px nav row */
  gap: var(--spacing-2);
}

.ground-appbar--medium .ground-appbar__title {
  font-size: var(--font-size-xl);
  font-weight: var(--font-weight-semibold);
  text-align: left;
  padding: var(--spacing-1) 0;
}

.ground-appbar--medium .ground-appbar__subtitle {
  font-size: var(--font-size-sm);
  color: var(--muted-foreground);
  line-height: var(--leading-snug);
}

/* ─── Title hidden (Small / Medium) ─── */
.ground-appbar--no-title .ground-appbar__title,
.ground-appbar--no-title .ground-appbar__subtitle {
  display: none;
}

/* ─── Glass variant ─── */
.ground-appbar--glass {
  background: color-mix(in srgb, var(--background) 70%, transparent);
  backdrop-filter: blur(20px) saturate(160%);
  -webkit-backdrop-filter: blur(20px) saturate(160%);
  border: 1px solid var(--border);
  margin: var(--spacing-2) var(--spacing-4) 0;
  border-radius: var(--radius-2xl);
}

/* ─── Large title variant ─── */
.ground-appbar--large .ground-appbar__large-title {
  padding: var(--spacing-2) var(--spacing-5);
  font-size: var(--font-size-3xl);
  font-weight: var(--font-weight-bold);
  letter-spacing: var(--font-tracking-tight);
  color: var(--foreground);
  transition: all var(--duration-normal-2) var(--easing-standard);
}

.ground-appbar--large.ground-appbar--collapsed .ground-appbar__large-title {
  height: 0;
  padding: 0;
  opacity: 0;
  overflow: hidden;
}

/* Reduced motion */
@media (prefers-reduced-motion: reduce) {
  .ground-appbar,
  .ground-appbar__back,
  .ground-appbar__action,
  .ground-appbar--large .ground-appbar__large-title {
    transition: none;
  }
}