# Frontend Hooks Module

## Overview

The Hooks module provides **47 custom React hooks** for reusable logic across the frontend application. Hooks handle everything from runtime presentation (preloading, navigation, transitions) to admin pages (tables, forms, filters), the constructor (elements, drag-drop), and React Query data fetching.

**Location:** `frontend/src/hooks/`

**Total Files:** 56 TypeScript files (41 hooks + 13 query hooks + 2 index files)

**Recent Refactors:**
1. **Page Navigation Consolidation:** 6+ fragmented hooks consolidated into `usePageNavigationState` state machine. See [Navigation State Machine](#usepagenavigationstate) for details.
2. **Video Hooks Module:** New `hooks/video/` directory with 8 primitive hooks for composable video playback. See [Video Hooks Module](./video-hooks-module.md) for details.
3. **Preloading Simplification:** Removed neighbor preloading (stream-first approach). Constructor always uses online mode - transition videos stream on-demand, then cache for replay.

---

## State Management Context

**Redux is the default** for app-wide state management. These hooks complement Redux by handling:
- **Ephemeral state** - Transient UI states that reset on unmount
- **Computed/derived values** - Data derived from Redux state
- **DOM interactions** - Refs, observers, event handlers
- **Session-scoped state** - State that doesn't persist across routes

See [Stores Module - State Management Guidelines](./stores-module.md#state-management-guidelines) for the decision tree on when to use Redux vs local hooks.

**Example:** `usePageNavigation` uses local `useState` because page history is session-scoped and isolated to a single route. If cross-component access or persistence were needed, it would be a Redux slice.

---

## Architecture

```
frontend/src/hooks/
├── index.ts                       # Central exports (tree-shaking friendly, 67 LOC)
│
├── Runtime/Preloading Hooks (10)
│   ├── usePreloadOrchestrator.ts      # Main asset preloading coordinator (~720 LOC) [SIMPLIFIED]
│   ├── usePageNavigationState.ts      # Unified page navigation state machine (~520 LOC)
│   ├── useTransitionPlayback.ts       # Video transition playback (~795 LOC)
│   ├── useSlideTransition.ts          # Slide transition animation (~180 LOC)
│   ├── usePageNavigation.ts           # Page navigation state + history (~195 LOC)
│   ├── useBackgroundVideoPlayback.ts  # Background video time control + play once (~225 LOC)
│   ├── useVideoSoundControl.ts        # iOS autoplay sound control (~100 LOC)
│   ├── usePageDataLoader.ts           # Project/page data loading (~253 LOC)
│   ├── usePageBackground.ts           # Page background management (~176 LOC)
│   └── useCanvasScale.ts              # Responsive canvas scaling (~110 LOC)
│
│   # DELETED (consolidated into usePageNavigationState):
│   # - usePageSwitch.ts (~475 LOC)
│   # - useBackgroundTransition.ts (~164 LOC)
│   # - useBackgroundUrls.ts (~104 LOC)
│
│   # DELETED (simplified preloading - no neighbor traversal):
│   # - useNeighborGraph.ts (~282 LOC)
│
├── Video Hooks (8)
│   ├── video/index.ts                     # Exports (~60 LOC)
│   ├── video/useVideoEventManager.ts      # Event listener management (~90 LOC)
│   ├── video/useVideoBufferingState.ts    # Buffering detection (~180 LOC)
│   ├── video/useVideoBlobUrl.ts           # Blob URL resolution (~150 LOC)
│   ├── video/useVideoFirstFrame.ts        # First frame detection (~130 LOC)
│   ├── video/useVideoErrorRecovery.ts     # Error handling + retry (~160 LOC)
│   ├── video/useVideoTimeouts.ts          # Timeout management (~80 LOC)
│   ├── video/useVideoPlaybackCore.ts      # Composite playback logic (~280 LOC)
│   └── video/useVideoPlayer.ts            # UI video player (~200 LOC)
│
├── Audio Hooks (2) - NEW
│   ├── audio/useAudioEventManager.ts      # Audio event listener management (~115 LOC)
│   └── useBackgroundAudioPlayback.ts      # Background audio playback + ducking (~220 LOC)
│
├── PWA/Offline Hooks (5)
│   ├── useOfflineMode.ts          # PWA offline management (~468 LOC)
│   ├── usePWAPreload.ts           # PWA asset preloading (~199 LOC)
│   ├── useStorageQuota.ts         # Storage quota monitoring (~110 LOC)
│   ├── useNetworkAware.ts         # Network condition monitoring (~163 LOC)
│   └── usePreloadProgress.ts      # Preload progress tracking (~220 LOC)
│
├── Constructor Hooks (10)
│   ├── useConstructorElements.ts      # Canvas element CRUD + local clipboard
│   ├── useCanvasElementDrag.ts        # Element drag handling (~150 LOC)
│   ├── useConstructorPageActions.ts   # Page save/create/duplicate support
│   ├── useConstructorData.ts          # Constructor data loading (~150 LOC)
│   ├── useTransitionPreview.ts        # Transition preview state (~184 LOC)
│   ├── useTransitionCreation.ts       # Transition creation state (~134 LOC)
│   ├── useCanvasElapsedTime.ts        # Canvas animation timing (~111 LOC)
│   ├── useMediaDurationProbe.ts       # Media duration detection (~219 LOC)
│   └── useBackdropEffect.ts           # Backdrop visual effects (~190 LOC)
│
├── Table/List Hooks (3)
│   ├── useEntityTable.ts          # Complete table state management (~288 LOC)
│   ├── useFilterItems.ts          # Filter state for data tables (~166 LOC)
│   └── useCSVHandling.ts          # CSV upload/download operations (~141 LOC)
│
├── Form Hooks (2)
│   ├── useEditPageSync.ts         # Edit page form sync (~166 LOC)
│   └── useFormSync.ts             # Form state management (~108 LOC)
│
├── UI Utility Hooks (10)
│   ├── useDraggable.ts            # Draggable panel management (~200 LOC)
│   ├── useOutsideClick.ts         # Click outside detection (~88 LOC)
│   ├── useElementEffects.ts       # Element interactive effects (~128 LOC)
│   ├── useIconPreload.ts          # Icon preloading (~176 LOC)
│   ├── useDashboardCounts.ts      # Dashboard entity counts (~308 LOC)
│   ├── useDevCompilationStatus.ts # Dev compilation status (~44 LOC)
│   ├── useProjectAssets.ts        # Project asset URL resolution (~102 LOC)
│   ├── useAssetOptions.ts         # Asset select options (~119 LOC)
│   ├── usePublishStatus.ts        # Publish/save timestamp status (~113 LOC)
│   └── useAudioEffects.ts         # Audio playback on hover/click (~305 LOC)
│
├── queries/                       # React Query data fetching hooks (13)
│   ├── index.ts                   # Query exports (~59 LOC)
│   ├── useAccessLogsQuery.ts      # Access logs query (~51 LOC)
│   ├── useAssetVariantsQuery.ts   # Asset variants query (~43 LOC)
│   ├── useAssetsQuery.ts          # Assets query (~109 LOC)
│   ├── useElementDefaultsQuery.ts # Element defaults query (~50 LOC)
│   ├── usePagesQuery.ts           # Tour pages query (~115 LOC)
│   ├── usePermissionsQuery.ts     # Permissions query (~35 LOC)
│   ├── useProjectAudioTracksQuery.ts # Audio tracks query (~109 LOC)
│   ├── useProjectMembershipsQuery.ts # Project memberships query (~94 LOC)
│   ├── useProjectQuery.ts         # Project query (~84 LOC)
│   ├── usePublishEventsQuery.ts   # Publish events query (~56 LOC)
│   ├── usePwaCachesQuery.ts       # PWA caches query (~67 LOC)
│   ├── useRolesQuery.ts           # Roles query (~112 LOC)
│   └── useUsersQuery.ts           # Users query (~126 LOC)
│
└── Exports
    └── index.ts                   # Tree-shaking friendly exports
```

---

## Hook Categories

### 1. Runtime/Preloading Hooks

These hooks power the runtime presentation viewer, handling asset preloading, page switching, and video transitions.

#### usePreloadOrchestrator

**File:** `usePreloadOrchestrator.ts` (~720 LOC)

**Purpose:** Main coordinator for asset preloading with priority queues and blob URL caching. Uses a **stream-first** approach - only preloads current page assets and outgoing transition videos.

```typescript
interface UsePreloadOrchestratorOptions {
  pages: PreloadPage[];
  pageLinks: PreloadPageLink[];
  elements: PreloadElement[];
  currentPageId: string | null;
  pageHistory?: string[];  // Used for detecting back navigation
  enabled?: boolean;
}

interface UsePreloadOrchestratorResult {
  isPreloading: boolean;
  currentPhase: 'idle' | 'phase1_current_page' | 'phase2_transitions';
  preloadedUrls: Set<string>;
  queueLength: number;
  /** Version counter that increments when blob URLs become ready (triggers re-renders) */
  readyUrlsVersion: number;
  preloadAsset: (url: string, priority?: number) => void;
  clearQueue: () => void;
  getCachedBlobUrl: (url: string) => Promise<string | null>;
  isUrlPreloaded: (url: string) => Promise<boolean>;
  getReadyBlobUrl: (url: string) => string | null;
}
```

**Key Features:**
- **Stream-first approach:** Only preloads current page + outgoing transitions (no neighbor preloading)
- Priority-based preload queue (transition videos +150, images +100)
- Two phases: Phase 1 (current page backgrounds) → Phase 2 (transition videos)
- Dual storage strategy: Cache API (< 5MB) vs IndexedDB (>= 5MB)
- Presigned URL management with proxy fallback
- Image pre-decoding for instant display
- O(1) blob URL lookup via `readyBlobUrlsRef`

**Recent Simplification:**
The hook was refactored to remove neighbor graph traversal (previously used `useNeighborGraph`). This simplifies the system:
- Constructor always uses online mode
- Transition videos stream on-demand, then cache for replay
- Eliminates network contention from aggressive preloading

**Usage:**
```typescript
const preloadOrchestrator = usePreloadOrchestrator({
  pages,
  pageLinks,
  elements,
  currentPageId,
  pageHistory,
  enabled: true,
});

// Get cached blob URL for instant display
const blobUrl = preloadOrchestrator.getReadyBlobUrl(originalUrl);

// Manually preload with high priority
preloadOrchestrator.preloadAsset(transitionVideoUrl, 150);
```

---

#### usePageNavigationState

**File:** `usePageNavigationState.ts` (~520 LOC)

**Purpose:** Unified state machine for page navigation using `useReducer` for atomic state transitions. Consolidates 6+ fragmented hooks to prevent race conditions.

**Consolidates:**
- `usePageSwitch` - URL resolution and switching
- `useBackgroundState` - Background ready tracking
- `useBackgroundTransition` - Fade-from-black effects
- `useTransitionCleanup` - Video cleanup coordination
- `useBackgroundUrls` - URL resolution for display
- `pageLoadingUtils` - Loading state computation

**State Machine Phases:**
```
┌──────────────────────────────────────────────────────────────────┐
│                    PAGE NAVIGATION STATE MACHINE                  │
├──────────────────────────────────────────────────────────────────┤
│   ┌───────┐   navigate()   ┌───────────┐                         │
│   │ IDLE  │ ─────────────► │ PREPARING │                         │
│   └───────┘                └─────┬─────┘                         │
│       ▲                    YES /    \ NO (has transition?)       │
│       │                       ▼      ▼                           │
│       │            ┌─────────────┐  ┌────────────┐               │
│       │            │TRANSITIONING│  │ LOADING_BG │               │
│       │            └──────┬──────┘  └─────┬──────┘               │
│       │            video ends      onBackgroundReady             │
│       │                   ▼               │                      │
│       │            ┌─────────────┐        │                      │
│       │            │TRANS_DONE   │        │                      │
│       │            └──────┬──────┘        │                      │
│       │          onBackgroundReady        │                      │
│       │                   ▼               ▼                      │
│       │            ┌────────────────────────┐                    │
│       │            │       FADING_IN        │                    │
│       │            └───────────┬────────────┘                    │
│       │               fade complete                              │
│       └────────────────────────┘                                 │
└──────────────────────────────────────────────────────────────────┘
```

```typescript
type NavigationPhase =
  | 'idle'           // No navigation in progress
  | 'preparing'      // Resolving URLs, saving previous state
  | 'transitioning'  // Video transition playing
  | 'transition_done'// Video finished, waiting for background
  | 'loading_bg'     // Direct navigation, waiting for background
  | 'fading_in';     // Black overlay fading out

interface UsePageNavigationStateResult {
  // Current state
  phase: NavigationPhase;

  // Current page URLs (for display)
  currentImageUrl: string;
  currentVideoUrl: string;
  currentAudioUrl: string;

  // Previous page URLs (for overlay)
  previousImageUrl: string;
  previousVideoUrl: string;

  // Derived states (computed from phase)
  isLoading: boolean;
  showSpinner: boolean;
  showElements: boolean;
  showPreviousOverlay: boolean;
  showTransitionVideo: boolean;
  isFadingIn: boolean;
  isSwitching: boolean;
  isNewBgReady: boolean;
  isBackgroundReady: boolean;
  pendingTransitionComplete: boolean;

  // Transition style for CSS
  transitionStyle: React.CSSProperties;

  // Actions
  navigateToPage: (targetPage, options?) => Promise<void>;
  onBackgroundReady: () => void;
  onTransitionEnded: () => void;
  setBackgroundDirectly: (imageUrl, videoUrl, audioUrl) => void;
  onVideoBufferStateChange: (isBuffering: boolean) => void;
}
```

**Key Benefits:**
| Before | After |
|--------|-------|
| 6+ hooks with 15+ state variables | 1 hook with 1 state object |
| Race conditions from async setState | Atomic transitions via useReducer |
| Invalid flag combinations possible | State machine prevents invalid states |
| Derived state scattered | All derived state in one useMemo |
| Hard to debug | Single phase value to inspect |

**Usage:**
```typescript
const navState = usePageNavigationState({
  preloadCache: preloadOrchestrator
    ? {
        getReadyBlobUrl: preloadOrchestrator.getReadyBlobUrl,
        getCachedBlobUrl: preloadOrchestrator.getCachedBlobUrl,
        preloadedUrls: preloadOrchestrator.preloadedUrls,
      }
    : undefined,
  transitionSettings,
});

// Navigate to a page
await navState.navigateToPage(targetPage, {
  hasTransition: false,
  isBack: false,
  onSwitched: () => applyPageSelection(targetPage.id, false),
});

// Use in CanvasBackground
<CanvasBackground
  backgroundImageUrl={navState.currentImageUrl}
  backgroundVideoUrl={navState.currentVideoUrl}
  previousBgImageUrl={navState.previousImageUrl}
  isSwitching={navState.isSwitching}
  isNewBgReady={navState.isNewBgReady}
  onBackgroundReady={navState.onBackgroundReady}
/>
```

**Context Provider:**
A `PageNavigationContext` is available for components that need access to navigation state:

```typescript
import { PageNavigationProvider, usePageNavigationContext } from '../context/PageNavigationContext';

// In parent component
<PageNavigationProvider preloadCache={...} transitionSettings={...}>
  <CanvasBackground />
  <Elements />
</PageNavigationProvider>

// In child component
const { phase, onBackgroundReady } = usePageNavigationContext();
```

---

#### useTransitionPlayback

**File:** `useTransitionPlayback.ts` (~795 LOC)

**Purpose:** Coordinates video transition playback with forward and pre-generated reversed video support.

```typescript
interface TransitionPlaybackOptions {
  transition: TransitionPreviewState | null;
  pendingPageId: string;
  transitionVideoRef: React.RefObject<HTMLVideoElement | null>;
  preloadOrchestrator?: UsePreloadOrchestratorResult;
  onTransitionComplete: (targetPageId: string) => void;
  onTransitionError?: (error: string) => void;
}

interface TransitionPlaybackResult {
  isPlaying: boolean;
  play: () => Promise<void>;
  stop: () => void;
  pendingTransitionComplete: boolean;
}
```

**Reverse Modes:**
| Mode | Description |
|------|-------------|
| `none` | Forward playback only |
| `separate` | Use pre-generated reversed video (server-side FFmpeg reversal) |

Reversed videos are pre-generated on the server when pages are saved, using
FFmpeg for audio/video synchronization.

**Source URL Selection:**
```typescript
const sourceUrl = useMemo(() => {
  if (!transition) return '';
  // Use reversed video if back navigation with separate reversed video
  if (transition.isBack && transition.reverseVideoUrl) {
    return transition.reverseVideoUrl;
  }
  return transition.videoUrl;
}, [transition]);
```

**Usage:**
```typescript
const transitionPlayback = useTransitionPlayback({
  transition: transitionPreview,
  pendingPageId,
  transitionVideoRef,
  preloadOrchestrator,
  onTransitionComplete: (targetId) => {
    pageSwitch.switchToPage(pages.find(p => p.id === targetId));
    transitionPreviewHook.closePreview();
  },
});
```

---

#### useSlideTransition

**File:** `useSlideTransition.ts` (~180 LOC)

**Purpose:** Manages slide transition animation state for Gallery and Carousel elements. Implements fade-through-overlay animation pattern.

**Animation Phases:**
```
Phase 1: Fade Out (half duration)
├── overlayOpacity: 0 → 1
└── slideOpacity: 1 → 0

Phase 2: Swap (at midpoint)
└── displayIndex switches to new slide

Phase 3: Fade In (half duration)
├── overlayOpacity: 1 → 0
└── slideOpacity: 0 → 1
```

```typescript
interface UseSlideTransitionReturn {
  currentIndex: number;        // Logical current index
  displayIndex: number;        // Visual index (lags during transition)
  phase: 'idle' | 'fadingOut' | 'fadingIn';
  isTransitioning: boolean;
  overlayOpacity: number;      // 0-1
  overlayColor: string;        // From settings
  goToIndex: (index: number) => void;
  setInitialIndex: (index: number) => void;
  slideTransitionStyle: CSSProperties;
  overlayTransitionStyle: CSSProperties;
  slideOpacity: number;        // Current slide visibility
}
```

**Usage:**
```typescript
import { useSlideTransition } from '../hooks/useSlideTransition';
import { resolveSlideTransition, extractCarouselSlideOverride } from '../lib/resolveSlideTransition';

// Resolve settings with cascade
const slideSettings = resolveSlideTransition(
  pageTransitionSettings,
  extractCarouselSlideOverride(element),
);

const {
  displayIndex,
  goToIndex,
  overlayOpacity,
  overlayColor,
  slideTransitionStyle,
  overlayTransitionStyle,
  slideOpacity,
} = useSlideTransition(slideSettings);

// Navigate
const handleNext = () => goToIndex((currentIndex + 1) % slides.length);

// Render
<img style={{ ...slideTransitionStyle, opacity: slideOpacity }} src={slides[displayIndex].imageUrl} />
<div style={{ ...overlayTransitionStyle, opacity: overlayOpacity, backgroundColor: overlayColor }} />
```

---

> **Note:** Runtime preloading is stream-first: the system preloads current page
> assets and outgoing transition videos.

---

#### usePageNavigation

**File:** `usePageNavigation.ts` (~195 LOC)

**Purpose:** Manages page navigation state with optional history tracking. Used by both `RuntimePresentation.tsx` and `constructor.tsx` for unified history management.

```typescript
interface UsePageNavigationResult<TPage extends NavigablePage> {
  currentPageId: string | null;
  currentPage: TPage | null;
  pageHistory: string[];
  previousPageId: string | null;
  defaultPage: TPage | null;
  setCurrentPageId: (pageId: string) => void;
  applyPageSelection: (targetPageId: string, isBack?: boolean) => void;
  isBackNavigation: (targetPageId: string) => boolean;
  goBack: () => boolean;
  resetHistory: () => void;
  /** Get navigation context for history-based back navigation */
  getNavigationContext: () => NavigationContext;
}
```

**Key Features:**
- **History limit**: `MAX_HISTORY_LENGTH = 50` prevents unbounded growth in long sessions
- **Browser-like back navigation**: History pops when `isBack=true` and target matches previous page
- **Navigation context**: `getNavigationContext()` provides `{ currentPageSlug, previousPageId }` for `resolveNavigationTarget()`
- **Unified state management**: Single source of truth for both constructor and runtime presentation

**Usage:**
```typescript
// Runtime mode with history (RuntimePresentation.tsx)
const {
  currentPageId: selectedPageId,
  pageHistory,
  applyPageSelection,
  getNavigationContext,
} = usePageNavigation({
  pages,
  defaultPageId: initialPageId,
  trackHistory: true,
});

// Constructor mode with history (constructor.tsx)
const {
  currentPageId: activePageId,
  pageHistory,
  applyPageSelection,
  getNavigationContext,
  setCurrentPageId: setActivePageId,
} = usePageNavigation({
  pages,
  trackHistory: true,
});

// Navigate with back flag (history pops on back)
applyPageSelection(targetPageId, isBack);

// Get context for history-based navigation
const navContext = getNavigationContext();
const navTarget = resolveNavigationTarget(element, pages, navContext);

// Go back programmatically
if (nav.goBack()) {
  console.log('Went back to', nav.previousPageId);
}
```

**History Behavior:**
```
Forward: A → B → C → history: [A, B, C]
Back to B (isBack=true): → history: [A, B]  ✓ Pops C
Back to A (isBack=true): → history: [A]     ✓ Pops B
Forward to D: → history: [A, D]             ✓ Adds D
```

---

> **Note:** `useBackgroundTransition` has been consolidated into `usePageNavigationState`. See [usePageNavigationState](#usepagenavigationstate) for the unified state machine.

---

#### useBackgroundVideoPlayback

**File:** `useBackgroundVideoPlayback.ts` (~225 LOC)

**Purpose:** Manages background video playback with custom start/end time control and "play once" functionality for tour pages.

```typescript
interface UseBackgroundVideoPlaybackOptions {
  videoUrl?: string;
  autoplay?: boolean;    // Default: true
  loop?: boolean;        // Default: true
  muted?: boolean;       // Default: true
  startTime?: number | null;  // Start playback at this time (seconds)
  endTime?: number | null;    // Stop/loop at this time (seconds)
  playOnce?: boolean;    // Default: false - play only once per session
  pageId?: string;       // Required for playOnce tracking
}

interface UseBackgroundVideoPlaybackResult {
  videoRef: RefObject<HTMLVideoElement | null>;
}
```

**Key Features:**
- Handles `loadedmetadata` event for initial seek to `startTime`
- Uses `timeupdate` event to enforce `endTime` boundary
- When `endTime` is set, handles looping via JavaScript (seeks back to `startTime`)
- Autoplay with browser policy handling (catch and ignore)
- **Play Once Mode:** When `playOnce` is true and `pageId` is provided:
  - Tracks played pages in a module-level `Set<string>` (`playedOncePages`)
  - On first visit: video plays normally, page ID added to Set on `ended` event
  - On subsequent visits: video seeks to last frame and pauses immediately
  - Session-scoped (resets on browser refresh, not persisted to storage)

**Usage:**
```typescript
const { videoRef } = useBackgroundVideoPlayback({
  videoUrl: page.background_video_url,
  autoplay: page.background_video_autoplay ?? true,
  loop: page.background_video_loop ?? true,
  muted: page.background_video_muted ?? true,
  startTime: page.background_video_start_time ?? null,
  endTime: page.background_video_end_time ?? null,
  playOnce: page.background_video_play_once ?? false,
  pageId: page.id,  // Required for play-once tracking
});

// Render video with ref
<video
  ref={videoRef}
  src={videoUrl}
  autoPlay={autoplay}
  loop={endTime == null ? loop : false}  // Use JS loop when endTime is set
  muted={muted}
  playsInline
/>
```

**Note:** When `endTime` is set, native HTML5 `loop` attribute should be disabled to allow the hook to handle looping via `timeupdate` event, properly seeking back to `startTime`.

---

#### useVideoSoundControl

**File:** `useVideoSoundControl.ts` (~100 LOC)

**Purpose:** Manages global presentation sound state with iOS autoplay compatibility. Presentation audio starts muted so visual media can autoplay, then background audio/video, element hover/click effects, media players, and gallery/info-panel videos can be unmuted by user interaction via a custom sound button.

```typescript
interface UseVideoSoundControlOptions {
  pageHasSound: boolean;        // Whether page settings allow sound
  hasBackgroundVideo: boolean;  // Whether page has a background video
  hasBackgroundAudio?: boolean; // Whether page has ambient/background audio
  hasElementAudio?: boolean;    // Whether elements can produce sound
  hasPresentationAudio?: boolean; // Whether any page in the presentation can produce sound
}

interface UseVideoSoundControlResult {
  isMuted: boolean;            // Current muted state (starts true)
  showSoundButton: boolean;    // Whether to show sound toggle button
  toggleSound: () => void;     // Toggle muted state
  setMuted: (muted: boolean) => void; // Force muted state
}
```

**Key Features:**
- Always starts muted for iOS autoplay compatibility
- Shows sound button when background video sound, background audio, element
  audio/video sound, or presentation-level audio exists
- Works with `RuntimeControls` sound toggle button
- Used by runtime presentations and constructor interact mode

**Usage:**
```tsx
const soundControl = useVideoSoundControl({
  pageHasSound: page.background_video_muted === false,
  hasBackgroundVideo: Boolean(backgroundVideoUrl),
  hasBackgroundAudio: Boolean(backgroundAudioUrl),
  hasPresentationAudio,
});

// Pass to CanvasBackground (always starts muted)
<CanvasBackground videoMuted={soundControl.isMuted} />

// Pass to RuntimeControls (sound toggle button)
<RuntimeControls
  showSoundButton={soundControl.showSoundButton}
  isMuted={soundControl.isMuted}
  onSoundToggle={soundControl.toggleSound}
/>
```

**iOS Autoplay Policy:**
- iOS WebKit blocks autoplay for unmuted videos
- By starting muted + providing custom sound button, native controls are avoided
- CSS in `main.css` hides native `-webkit-media-controls-*` as fallback

---

### Audio Hooks

#### useAudioEventManager

**File:** `audio/useAudioEventManager.ts` (~115 LOC)

**Purpose:** Manages audio element event listener setup and cleanup with a declarative API. Mirrors the `useVideoEventManager` pattern for consistency.

```typescript
interface UseAudioEventManagerOptions {
  audioRef: RefObject<HTMLAudioElement | null>;
  enabled?: boolean;
  handlers: AudioEventHandlers;
}

interface AudioEventHandlers {
  onLoadedMetadata?: (event: Event) => void;
  onLoadedData?: (event: Event) => void;
  onCanPlay?: (event: Event) => void;
  onPlaying?: (event: Event) => void;
  onPause?: (event: Event) => void;
  onEnded?: (event: Event) => void;
  onTimeUpdate?: (event: Event) => void;
  onError?: (event: Event) => void;
  // ... other audio events
}
```

**Usage:**
```typescript
useAudioEventManager({
  audioRef,
  enabled: Boolean(audioUrl),
  handlers: {
    onLoadedMetadata: () => seekToStartTime(),
    onTimeUpdate: () => enforceEndTime(),
    onEnded: () => markAsPlayed(),
  },
});
```

---

#### useBackgroundAudioPlayback

**File:** `useBackgroundAudioPlayback.ts` (~220 LOC)

**Purpose:** Manages background audio playback with custom start/end time control, session-scoped "play once" tracking, and integration with audio ducking system.

```typescript
interface UseBackgroundAudioPlaybackOptions {
  audioUrl?: string;              // Audio URL (may be blob URL)
  audioStoragePath?: string;      // Original storage path for play-once tracking
  autoplay?: boolean;             // Default: true
  loop?: boolean;                 // Default: true
  startTime?: number | null;      // Start playback at time (seconds)
  endTime?: number | null;        // Stop/loop at time (seconds)
  paused?: boolean;               // External pause control (for ducking)
}

interface UseBackgroundAudioPlaybackResult {
  audioRef: RefObject<HTMLAudioElement | null>;
  shouldBlockAutoplay: boolean;   // True if audio already played this session
}
```

**Key Features:**
- **Start/End Time Control:** Seeks to `startTime` on load, loops or pauses at `endTime`
- **Play Once Tracking:** Session-scoped Set tracks played audio (cleared on browser refresh)
- **Audio Ducking Integration:** Registers with `backgroundAudioController` for automatic pause/resume when element audio plays
- **Graceful Autoplay:** Handles browser autoplay restrictions silently

**Usage:**
```typescript
const { audioRef } = useBackgroundAudioPlayback({
  audioUrl: page.background_audio_url,
  autoplay: page.background_audio_autoplay ?? true,
  loop: page.background_audio_loop ?? true,
  startTime: page.background_audio_start_time ?? null,
  endTime: page.background_audio_end_time ?? null,
});

// Render audio with ref
<audio ref={audioRef} src={audioUrl} preload="auto" hidden />
```

**Audio Ducking:** When element hover/click audio starts playing, background audio is automatically paused via `backgroundAudioController`. When element audio ends, background audio resumes.

---

#### useCanvasScale

**File:** `useCanvasScale.ts` (~110 LOC)

**Purpose:** Manages responsive canvas scaling with letterbox mode for maintaining design aspect ratio across different viewport sizes. Core hook of the UI Adaptivity System.

> **See:** [UI Adaptivity System](ui-adaptivity-system.md) for complete documentation including canvas units, letterbox mode, and element styling.

```typescript
interface UseCanvasScaleOptions {
  designWidth?: number;    // Design canvas width (default: 1920)
  designHeight?: number;   // Design canvas height (default: 1080)
}

interface UseCanvasScaleResult {
  scale: number;                    // Current scale factor (1.0 = design size)
  designWidth: number;              // Design width (from options or default)
  designHeight: number;             // Design height (from options or default)
  canvasWidth: number;              // Actual canvas width in pixels
  canvasHeight: number;             // Actual canvas height in pixels
  isPortrait: boolean;              // Whether viewport is portrait orientation
  showRotatePrompt: boolean;        // Whether to show rotate prompt
  cssVars: CSSProperties;           // CSS custom properties for scaling
  letterboxStyles: CSSProperties;   // Styles for centered letterbox container
}
```

**Key Features:**
- Calculates scale factor: `min(viewportWidth/designWidth, viewportHeight/designHeight)`
- Provides CSS custom properties (`--cu`, `--canvas-scale`, `--design-width`, `--design-height`)
- Generates letterbox styles for centered canvas with black bars
- Handles portrait orientation detection with rotate prompt

**CSS Custom Properties:**
| Property | Description | Example |
|----------|-------------|---------|
| `--cu` | Canvas unit (1 design pixel) | `calc(1px * 0.75)` |
| `--canvas-scale` | Current scale factor | `0.75` |
| `--design-width` | Design canvas width | `1920` |
| `--design-height` | Design canvas height | `1080` |

**Usage:**
```typescript
const { cssVars, letterboxStyles, isPortrait, showRotatePrompt } = useCanvasScale({
  designWidth: project?.design_width,
  designHeight: project?.design_height,
});

// Apply to canvas container
<div className="bg-black w-screen h-screen overflow-hidden">
  <div style={{ ...cssVars, ...letterboxStyles }}>
    {/* Canvas content - all children can use var(--cu) */}
  </div>
</div>
```

**Integration with Element Styles:**
```typescript
import { toCU } from '../lib/canvasScale';

// Elements use canvas units for responsive sizing
<button style={{
  fontSize: toCU(16),      // "calc(16 * var(--cu, 1px))"
  padding: toCU(12),       // Scales with viewport
  borderRadius: toCU(8),
}}>
  Click me
</button>
```

---

#### usePageDataLoader

**File:** `usePageDataLoader.ts` (~253 LOC)

**Purpose:** Loads project and page data for runtime and constructor.

```typescript
interface UsePageDataLoaderResult {
  project: Project | null;
  pages: TourPage[];
  elements: CanvasElement[];
  pageLinks: PreloadPageLink[];
  isLoading: boolean;
  error: string | null;
  reload: (preservePageId?: string) => Promise<void>;
}
```

---

### 2. PWA/Offline Hooks

Hooks for Progressive Web App functionality including offline caching and network monitoring.

#### useOfflineMode

**File:** `useOfflineMode.ts` (~468 LOC)

**Purpose:** Full offline mode management with download progress tracking.

```typescript
interface UseOfflineModeOptions {
  projectId: string | null;
  projectSlug?: string;
  projectName?: string;
  enabled?: boolean;
}

interface UseOfflineModeResult {
  // Status
  isOfflineCapable: boolean;
  isDownloaded: boolean;
  isDownloading: boolean;
  status: ProjectOfflineStatus;
  progress: number;
  downloadedAssets: number;
  totalAssets: number;
  downloadedBytes: number;
  totalBytes: number;
  error: string | null;

  // Actions
  startDownload: () => Promise<void>;
  pauseDownload: () => void;
  resumeDownload: () => void;
  cancelDownload: () => void;
  deleteOfflineData: () => Promise<void>;
  checkForUpdates: () => Promise<boolean>;

  // Info
  projectInfo: OfflineProject | null;
  estimatedSize: number;
  formatSize: (bytes: number) => string;
}
```

**Usage:**
```typescript
const offlineMode = useOfflineMode({
  projectId,
  projectSlug,
  projectName,
  enabled: true,
});

// Start download
await offlineMode.startDownload();

// Check progress
console.log(`Downloaded: ${offlineMode.progress}%`);
console.log(`${offlineMode.downloadedAssets}/${offlineMode.totalAssets} assets`);
console.log(`Size: ${offlineMode.formatSize(offlineMode.downloadedBytes)}`);
```

---

#### useStorageQuota

**File:** `useStorageQuota.ts` (~110 LOC)

**Purpose:** Monitors storage quota and usage for offline assets.

```typescript
interface UseStorageQuotaResult extends StorageQuotaInfo {
  isLoading: boolean;
  error: string | null;
  refresh: () => Promise<void>;
  requestPersistence: () => Promise<boolean>;
  isPersisted: boolean;
  isWarning: boolean;   // >= warningPercent (default 70%)
  isCritical: boolean;  // >= criticalPercent (default 90%)
  formatSize: (bytes: number) => string;
}
```

---

#### useNetworkAware

**File:** `useNetworkAware.ts` (~163 LOC)

**Purpose:** Monitors network conditions and adapts preloading strategy.

```typescript
interface UseNetworkAwareResult {
  networkInfo: NetworkInfo;
  shouldPreloadAggressively: boolean;  // 4G or high downlink
  preferLowQuality: boolean;           // slow-2g, 2g, or saveData
  recommendedConcurrency: number;      // 1-3 based on connection
  suggestOfflineMode: boolean;         // Poor connection detected
}
```

**Network Concurrency Table:**
| Connection | Concurrency |
|------------|-------------|
| slow-2g | 1 |
| 2g | 1 |
| 3g | 2 |
| 4g | 3 |

---

#### usePWAPreload

**File:** `usePWAPreload.ts` (~199 LOC)

**Purpose:** Orchestrates asset preloading for PWA offline caching with progress tracking.

```typescript
interface PreloadState {
  isPreloading: boolean;
  progress: number;
  loadedCount: number;
  totalCount: number;
  errors: string[];
}

const result = usePWAPreload({
  assets: [
    { url: 'image.jpg', type: 'image' },
    { url: 'video.mp4', type: 'video' },
  ],
  onComplete: () => console.log('Done!'),
  skipIfCached: true,
});
```

---

### 3. Constructor Hooks

Hooks for the visual tour builder (constructor.tsx).

#### useConstructorElements

**File:** `useConstructorElements.ts`

**Purpose:** Canvas element CRUD operations with selection management, nested
gallery/carousel/info-panel item helpers, and constructor-local element
copy/paste clipboard.

```typescript
interface UseConstructorElementsOptions {
  initialElements?: CanvasElement[];
  elementDefaultsByType?: Partial<Record<CanvasElementType, Partial<CanvasElement>>>;
  allowedNavigationTypes?: NavigationElementType[];
  onElementsChange?: (elements: CanvasElement[]) => void;
  initialSelectedElementId?: string;
  onElementSelected?: (elementId: string) => void;
  onSelectionCleared?: () => void;
  onElementAdded?: (element: CanvasElement) => void;
  onElementRemoved?: (elementId: string) => void;
  onElementCopied?: (element: CanvasElement) => void;
  onElementPasted?: (element: CanvasElement) => void;
}

interface UseConstructorElementsResult {
  elements: CanvasElement[];
  setElements: React.Dispatch<React.SetStateAction<CanvasElement[]>>;
  getElements: () => CanvasElement[];
  selectedElementId: string;
  selectedElement: CanvasElement | null;
  copiedElement: CanvasElement | null;
  canPasteElement: boolean;
  selectElement: (elementId: string) => void;
  clearSelection: () => void;
  addElement: (type: CanvasElementType) => void;
  updateSelectedElement: (patch: Partial<CanvasElement>) => void;
  updateElement: (elementId: string, patch: Partial<CanvasElement>) => void;
  removeSelectedElement: () => void;
  copySelectedElement: () => void;
  pasteCopiedElement: () => CanvasElement | null;
  removeElement: (elementId: string) => void;

  // Gallery cards
  galleryCards: {
    add: () => void;
    update: (cardId: string, patch: Partial<GalleryCard>) => void;
    remove: (cardId: string) => void;
  };

  // Gallery info spans
  galleryInfoSpans: {
    add: () => void;
    update: (spanId: string, text: string) => void;
    remove: (spanId: string) => void;
  };

  // Carousel slides
  carouselSlides: {
    add: () => void;
    update: (slideId: string, patch: Partial<CarouselSlide>) => void;
    remove: (slideId: string) => void;
  };

  updateElementPosition: (elementId: string, xPercent: number, yPercent: number) => void;
  bringToFront: (elementId: string) => void;
  sendToBack: (elementId: string) => void;
}
```

`setElements` is wrapped by the hook so it updates both React state and an
internal `elementsRef`. `getElements()` reads that ref synchronously. This is
required for same-tick flows such as Paste followed immediately by Save or Save
to Stage, where React may not have committed the visible re-render yet.

Element copy/paste uses `cloneElementForPaste()` from `lib/elementDefaults.ts`.
The clone preserves all non-identity settings, including CSS styles, effects,
media, links, navigation targets, transition fields, dimensions, and position.
Only the top-level element ID and nested gallery/carousel/info-panel item IDs are
regenerated.

**Usage:**
```typescript
const {
  elements,
  getElements,
  selectedElement,
  addElement,
  updateSelectedElement,
  updateElement,
  copySelectedElement,
  pasteCopiedElement,
  canPasteElement,
  galleryCards,
  galleryInfoSpans,
} = useConstructorElements({
  initialElements,
  onElementsChange: setElements,
  elementDefaultsByType,
});

// Add a button element
addElement('button');

// Update selected element
updateSelectedElement({ label: 'New Label' });

// Update element by ID
updateElement(elementId, { xPercent: 50 });

// Add gallery card to selected gallery
galleryCards.add();

// Add info span to selected gallery
galleryInfoSpans.add();

// Toolbar copy/paste actions
copySelectedElement();
if (canPasteElement) pasteCopiedElement();
```

---

#### useCanvasElementDrag

**File:** `useCanvasElementDrag.ts` (~150 LOC)

**Purpose:** Handles element dragging on the constructor canvas.

```typescript
interface UseCanvasElementDragResult {
  isDragging: boolean;
  onDragStart: (event: React.MouseEvent, elementId: string) => void;
  onDragEnd: () => void;
}
```

**Usage:**
```typescript
const { isDragging, onDragStart, onDragEnd } = useCanvasElementDrag({
  canvasRef,
  elements,
  onPositionChange: (elementId, xPercent, yPercent) => {
    updateElementPosition(elementId, xPercent, yPercent);
  },
});

// Attach to element
<div
  onMouseDown={(e) => onDragStart(e, element.id)}
  onMouseUp={onDragEnd}
>
```

---

#### useConstructorPageActions

**File:** `useConstructorPageActions.ts`

**Purpose:** Page create/save/publish operations in constructor, including page
duplication orchestration.

```typescript
interface UseConstructorPageActionsOptions {
  activePageId: string;
  elements: CanvasElement[];
  getElements?: () => CanvasElement[];
  pageBackground: PageBackgroundState;
  onReload: () => Promise<void>;
}

interface UseConstructorPageActionsResult {
  isSaving: boolean;
  isSavingToStage: boolean;
  isCreatingPage: boolean;
  isDuplicatingPage: boolean;
  isCreatingTransition: boolean;
  saveConstructor: () => Promise<void>;
  saveToStage: () => Promise<void>;
  createPage: () => Promise<void>;
  duplicatePage: (sourcePageId: string, name: string, slug: string) => Promise<TourPage | null>;
  createTransition: (params: TransitionParams) => Promise<void>;
}
```

`saveConstructor()` serializes `getElements?.() ?? elements` into
`tour_pages.ui_schema_json.elements`. Passing `getElements` from
`useConstructorElements` keeps pasted elements from being dropped if Save/Stage
is clicked immediately after Paste.

Page duplication saves the active page first, then calls
`POST /api/tour_pages/:id/duplicate`; the backend creates an independent dev
page at the end of the presentation order. Page deletion itself is triggered
from `constructor.tsx` so the page can show the shared confirmation modal and
choose the next active page after the API call.

---

#### useTransitionPreview

**File:** `useTransitionPreview.ts` (~200 LOC)

**Purpose:** Manages transition video preview state in constructor.

```typescript
interface UseTransitionPreviewResult {
  preview: TransitionPreviewState | null;
  pendingPageId: string;
  openPreview: (element: TransitionElement, direction: 'forward' | 'back') => void;
  openPreviewWithTarget: (element: TransitionElement, direction: 'forward' | 'back', targetPageId: string) => void;
  closePreview: () => void;
  isActive: boolean;
}
```

---

### 4. Table/List Hooks

Hooks for admin data tables.

#### useEntityTable

**File:** `useEntityTable.ts` (~296 LOC)

**Purpose:** Complete state management for entity data tables.

```typescript
interface UseEntityTableReturn<T> {
  data: T[];
  columns: GridColDef[];
  loading: boolean;
  count: number;

  // Pagination
  currentPage: number;
  setCurrentPage: (page: number) => void;
  numPages: number;

  // Sorting
  sortModel: GridSortModel;
  setSortModel: (model: GridSortModel) => void;

  // Selection
  selectedRows: string[];
  setSelectedRows: (ids: string[]) => void;

  // Filtering
  filterItems: FilterItem[];
  handleFilterSubmit: () => void;
  handleFilterReset: () => void;

  // Actions
  handleDeleteClick: (id: string) => void;
  handleDeleteConfirm: () => Promise<void>;
  handleRowUpdate: (id: string, data: Partial<T>) => Promise<void>;

  // Data loading
  loadData: (page?: number, request?: string) => void;
}
```

**Usage:**
```typescript
const tableProps = useEntityTable<User>({
  entityName: 'users',
  entityNamePlural: 'users',
  fetchAction: usersFetch,
  deleteAction: usersDelete,
  configureColumns: configureUsersCols,
  filters: usersFilters,
});

// In component
<DataGrid
  rows={tableProps.data}
  columns={tableProps.columns}
  loading={tableProps.loading}
  sortModel={tableProps.sortModel}
  onSortModelChange={tableProps.setSortModel}
/>
```

---

#### useFilterItems

**File:** `useFilterItems.ts` (~166 LOC)

**Purpose:** Manages filter state for data tables.

```typescript
interface UseFilterItemsReturn {
  filterItems: FilterItem[];
  setFilterItems: (items: FilterItem[]) => void;
  addFilter: () => void;
  removeFilter: (id: string) => void;
  updateFilter: (id: string, fields: Partial<FilterFields>) => void;
  resetFilters: () => void;
  generateFilterRequest: () => string;
  filterRequest: FilterRequest;
}
```

**Usage:**
```typescript
const filters: Filter[] = [
  { title: 'name', label: 'Name' },
  { title: 'status', label: 'Status', type: 'enum', options: ['active', 'inactive'] },
  { title: 'created_at', label: 'Created', date: true },
];

const { filterItems, addFilter, generateFilterRequest } = useFilterItems(filters);

// Add filter
addFilter();

// Generate query string
const queryString = generateFilterRequest(); // "&name=john&statusRange=active"
```

---

#### useCSVHandling

**File:** `useCSVHandling.ts` (~141 LOC)

**Purpose:** CSV upload and download operations.

```typescript
interface UseCSVHandlingReturn {
  csvFile: File | null;
  setCsvFile: (file: File | null) => void;
  isModalActive: boolean;
  setIsModalActive: (active: boolean) => void;
  isUploading: boolean;
  isDownloading: boolean;
  downloadCSV: () => Promise<void>;
  uploadCSV: () => Promise<void>;
  error: string | null;
}
```

---

### 5. Form Hooks

Hooks for form management in edit pages.

#### useEditPageSync

**File:** `useEditPageSync.ts` (~166 LOC)

**Purpose:** Syncs edit page forms with Redux entity state.

```typescript
interface UseEditPageSyncOptions<T> {
  entitySelector: (state: RootState) => unknown;
  fetchAction: AsyncThunk<unknown, { id?: string; query?: string }, object>;
  initialValues: T;
  postProcess?: (entity: T, initial: T) => T;
  idOverride?: string;
}

interface UseEditPageSyncReturn<T> {
  values: T;
  setValues: React.Dispatch<React.SetStateAction<T>>;
  id: string | null;
  isLoading: boolean;
  isFound: boolean;
}
```

**Usage:**
```typescript
const initVals = { name: '', permissions: [] };

const { values, id, isLoading } = useEditPageSync({
  entitySelector: (state) => state.roles.roles,
  fetchAction: fetch,
  initialValues: initVals,
  postProcess: (entity, initial) => ({
    ...entity,
    permissions: entity.permissions?.map(p => ({ value: p.id, label: p.name })) || [],
  }),
});

// Use in Formik
<Formik enableReinitialize initialValues={values} onSubmit={handleSubmit}>
```

---

#### useFormSync

**File:** `useFormSync.ts` (~108 LOC)

**Purpose:** Generic form state management with field tracking.

```typescript
interface UseFormSyncReturn<T> {
  values: T;
  setFieldValue: (field: keyof T, value: T[keyof T]) => void;
  setValues: (values: Partial<T>) => void;
  resetForm: () => void;
  isDirty: boolean;
  dirtyFields: Set<keyof T>;
}
```

---

### 6. UI Utility Hooks

General-purpose utility hooks.

#### useDraggable

**File:** `useDraggable.ts` (~200 LOC)

**Purpose:** Generic draggable panel management with pointer tracking.

```typescript
interface UseDraggableResult {
  position: Position;
  setPosition: (position: Position) => void;
  isDragging: boolean;
  onDragStart: (event: React.MouseEvent) => void;
  onDragStartIgnoreButtons: (event: React.MouseEvent) => void;
}
```

**Usage:**
```typescript
const { position, onDragStart, isDragging } = useDraggable({
  initialPosition: { x: 20, y: 20 },
  elementWidth: 400,
  elementHeight: 300,
});

<div style={{ left: position.x, top: position.y }}>
  <div onMouseDown={onDragStart}>Drag Handle</div>
  <div>Content</div>
</div>
```

---

#### useOutsideClick

**File:** `useOutsideClick.ts` (~88 LOC)

**Purpose:** Detects clicks outside specified elements.

```typescript
useOutsideClick({
  containerRef: panelRef,
  ignoreRefs: [buttonRef],
  ignoreDataAttribute: 'data-element-id',
  selectedValue: selectedElementId,
  onOutsideClick: () => setSelectedId(''),
  enabled: !!selectedId,
});
```

---

#### useElementEffects

**File:** `useElementEffects.ts` (~128 LOC)

**Purpose:** Manages element interactive effects (hover, focus, active) at runtime. Exposes internal state for integration with other hooks (e.g., `useAudioEffects`).

```typescript
interface UseElementEffectsResult {
  effectStyle: CSSProperties;
  eventHandlers: {
    onMouseEnter: () => void;
    onMouseLeave: () => void;
    onFocus: () => void;
    onBlur: () => void;
    onMouseDown: () => void;
    onMouseUp: () => void;
    onTouchStart: () => void;
    onTouchEnd: () => void;
  };
  onPersistClick: () => void;
  /** Exposed state for audio effects integration */
  state: {
    isHovered: boolean;
    isActive: boolean;
  };
}
```

**Priority:** active > focus > hover > base

**Usage:**
```typescript
const { effectStyle, eventHandlers, state: effectState } = useElementEffects(element);

// Use effectState for audio integration
useAudioEffects({
  isHovered: effectState.isHovered,
  isActive: effectState.isActive,
  // ...
});

<div style={{ ...baseStyle, ...effectStyle }} {...eventHandlers}>
  {content}
</div>
```

---

#### useAudioEffects

**File:** `useAudioEffects.ts` (~305 LOC)

**Purpose:** Manages audio playback for element hover and click effects. Uses HTML5 Audio API for lightweight, non-visual audio playback with authenticated URL support.

```typescript
interface UseAudioEffectsOptions {
  /** URL of audio to play on hover */
  hoverAudioUrl?: string;
  /** URL of audio to play on click/active */
  clickAudioUrl?: string;
  /** Volume level 0-1 (iOS ignores this) */
  volume?: number;
  /** Current hover state from useElementEffects */
  isHovered: boolean;
  /** Current active/pressed state from useElementEffects */
  isActive: boolean;
  /** Optional URL resolver for preloaded blob URLs */
  resolveUrl?: (url: string | undefined) => string;
  /** Reset key to stop audio (e.g., element ID or page slug) */
  resetKey?: string | number;
}

interface UseAudioEffectsResult {
  /** Manually trigger click audio playback */
  playClickAudio: () => void;
  /** Stop all audio playback */
  stopAll: () => void;
}
```

**Key Features:**
- **Hover audio**: Plays to completion once started (not interrupted by mouse leave)
- **Click audio**: Interruptible - clicking again restarts from beginning
- **Authenticated URLs**: Fetches audio via `fetch()` with credentials, creates blob URLs
- **Caching**: Tracks fetched URLs to prevent duplicate requests
- **Mobile support**: Touch events (via `useElementEffects`) trigger hover audio

**Cross-Browser Compatibility:**

| Feature | Chrome | Firefox | Safari | iOS Safari | Android |
|---------|--------|---------|--------|------------|---------|
| HTML5 Audio | ✅ | ✅ | ✅ | ✅ | ✅ |
| Volume control | ✅ | ✅ | ✅ | ❌ (iOS ignores) | ✅ |
| Autoplay (click) | ✅ | ✅ | ✅ | ✅ (after tap) | ✅ |

**Usage:**
```typescript
// In CanvasElement.tsx or RuntimeElement.tsx
const { effectStyle, eventHandlers, state: effectState } = useElementEffects(
  isEditMode ? {} : effectProperties,
);

// Audio effects - only active in preview mode (not edit mode)
useAudioEffects({
  hoverAudioUrl: isEditMode ? undefined : effectProperties.hoverAudioUrl,
  clickAudioUrl: isEditMode ? undefined : effectProperties.clickAudioUrl,
  volume: parseFloat(effectProperties.audioVolume || '1'),
  isHovered: effectState.isHovered,
  isActive: effectState.isActive,
  resolveUrl,  // Resolves to preloaded blob URLs
  resetKey: element.id,
});
```

**Integration with Element Effects:**
The hook depends on `useElementEffects` for hover/active state. The `isHovered` and `isActive` states are passed through to trigger audio playback at the right moments.

**Constructor vs Runtime:**
- **Constructor Edit Mode**: Audio disabled (`hoverAudioUrl: undefined`)
- **Constructor Preview Mode**: Audio enabled (press F5 to test)
- **Runtime Presentation**: Audio enabled

---

#### useDashboardCounts

**File:** `useDashboardCounts.ts` (~308 LOC)

**Purpose:** Fetches entity counts for dashboard with permission filtering.

```typescript
interface UseDashboardCountsReturn {
  counts: Record<string, EntityCountValue>;
  loading: boolean;
  error: Error | null;
  refetch: () => Promise<void>;
  getCount: (key: string) => EntityCountValue;
  getVisibleEntities: () => EntityConfig[];
}
```

**Dashboard Entities:**
- users, roles, permissions, projects
- project_memberships, assets, asset_variants
- presigned_url_requests, tour_pages, project_audio_tracks
- publish_events, pwa_caches, access_logs

---

#### useProjectAssets

**File:** `useProjectAssets.ts` (~95 LOC)

**Purpose:** Preloads and resolves project assets (favicon, og_image, logo) to presigned URLs. Handles both `storage_key` (relative paths) and legacy `cdn_url` (full S3 URLs) formats.

```typescript
interface ProjectAssetInput {
  favicon_url?: string;
  og_image_url?: string;
  logo_url?: string;
}

interface ProjectAssets {
  faviconUrl: string | null;
  ogImageUrl: string | null;
  logoUrl: string | null;
  isLoading: boolean;
}

function useProjectAssets(project: ProjectAssetInput | null): ProjectAssets;
```

**Key Features:**
- Extracts storage paths from URLs (handles both formats)
- Queues presigned URL requests for relative paths
- Resolves to playback URLs (presigned if available, otherwise proxy)
- Tracks URL changes to avoid redundant processing

**Usage:**
```typescript
const { faviconUrl, ogImageUrl, logoUrl, isLoading } = useProjectAssets(project);

// Use resolved URLs
{faviconUrl && <link rel="icon" href={faviconUrl} />}
{ogImageUrl && <meta property="og:image" content={ogImageUrl} />}
{logoUrl && <img src={logoUrl} alt="Logo" />}
```

---

#### usePublishStatus

**File:** `usePublishStatus.ts` (~113 LOC)

**Purpose:** Fetches the last successful publish/save events for a project to display timestamps in the UI. Follows the `useDashboardCounts` pattern with `mountedRef` and parallel API calls.

```typescript
interface UsePublishStatusOptions {
  projectId: string | null;
}

interface UsePublishStatusResult {
  /** Last successful dev → stage save timestamp */
  lastSavedToStage: string | null;
  /** Last successful stage → production publish timestamp */
  lastPublishedToProduction: string | null;
  /** Whether data is loading */
  isLoading: boolean;
  /** Refresh the status (call after new publish) */
  refresh: () => Promise<void>;
}
```

**Key Features:**
- Fetches both dev→stage and stage→production events in parallel via `Promise.all`
- Uses `mountedRef` pattern to prevent state updates after unmount
- Queries `publish_events` API with `projectId`, environment filters, and `status: 'success'`
- Returns `finished_at` timestamp of most recent successful event

**Usage:**
```typescript
// In Project Dashboard (pages/projects/[projectsId].tsx)
const { lastPublishedToProduction, refresh: refreshPublishStatus } = usePublishStatus({
  projectId,
});

// Display in button subtitle
<BaseButton
  label="Publish to Production"
  subtitle={lastPublishedToProduction
    ? `Last: ${dataFormatter.relativeTimestamp(lastPublishedToProduction)}`
    : undefined}
  onClick={() => setIsPublishModalActive(true)}
/>

// Refresh after successful publish
const handlePublish = async () => {
  await axios.post('/publish', { projectId, title, description });
  await refreshPublishStatus();
};

// In Constructor (pages/constructor.tsx)
const { lastSavedToStage, refresh: refreshPublishStatus } = usePublishStatus({
  projectId,
});

// Project-level save timestamp: most recent updatedAt across all pages
const lastProjectSaveAt = useMemo(() => {
  if (!pages.length) return null;
  return pages.reduce((latest, page) => {
    if (!page.updatedAt) return latest;
    if (!latest) return page.updatedAt;
    return new Date(page.updatedAt) > new Date(latest) ? page.updatedAt : latest;
  }, null as string | null);
}, [pages]);

// Wrap saveToStage to refresh status
const handleSaveToStage = useCallback(async () => {
  await saveToStage();
  await refreshPublishStatus();
}, [saveToStage, refreshPublishStatus]);

// Pass timestamps to ConstructorMenu
<ConstructorMenu
  lastSavedAt={lastProjectSaveAt}  // Project-level, not page-level
  lastSavedToStageAt={lastSavedToStage}
  onSaveToStage={handleSaveToStage}
/>
```

**Integration with dataFormatter:**
```typescript
import dataFormatter from '../../helpers/dataFormatter';

// Format timestamp for display
dataFormatter.relativeTimestamp(lastPublishedToProduction);
// → "Just now", "5 min ago", "2 hours ago", "Today at 14:30", "Apr 28 at 16:45"
```

---

## Index Exports

**File:** `index.ts` (~44 LOC)

The index file exports hooks and their types for tree-shaking friendly imports:

```typescript
// Exported from index.ts (centralized)
export { useFilterItems } from './useFilterItems';
export { useCSVHandling } from './useCSVHandling';
export { useFormSync } from './useFormSync';
export { useEntityTable } from './useEntityTable';
export { useTransitionPlayback } from './useTransitionPlayback';
export type { ReverseMode, TransitionConfig, UseTransitionPlaybackOptions,
              PlaybackPhase, UseTransitionPlaybackResult } from './useTransitionPlayback';
export { usePageNavigation } from './usePageNavigation';
export type { NavigablePage, UsePageNavigationOptions,
              UsePageNavigationResult } from './usePageNavigation';
export { usePageNavigationState } from './usePageNavigationState';
export type { NavigationPhase, UsePageNavigationStateOptions,
              UsePageNavigationStateResult } from './usePageNavigationState';
export { useBackgroundVideoPlayback } from './useBackgroundVideoPlayback';
export type { UseBackgroundVideoPlaybackOptions,
              UseBackgroundVideoPlaybackResult } from './useBackgroundVideoPlayback';
export { useVideoSoundControl } from './useVideoSoundControl';
export type { UseVideoSoundControlOptions,
              UseVideoSoundControlResult } from './useVideoSoundControl';
export { usePageDataLoader } from './usePageDataLoader';
export type { UsePageDataLoaderOptions, UsePageDataLoaderResult } from './usePageDataLoader';

// Import directly for better tree-shaking (not in index.ts)
// - usePreloadOrchestrator
// - useNeighborGraph
// - useConstructorElements
// - useCanvasElementDrag
// - useTransitionPreview
// - useOfflineMode
// - useOutsideClick
// - useCanvasElapsedTime
// - useDraggable
// - useMediaDurationProbe
// - useIconPreload
// - useProjectAssets
```

---

## Design Patterns

### 1. Options/Result Pattern

All hooks follow a consistent interface pattern:

```typescript
interface UseXxxOptions {
  // Configuration inputs
}

interface UseXxxResult {
  // State and methods
}

function useXxx(options: UseXxxOptions): UseXxxResult {
  // Implementation
}
```

### 2. Callback Refs

Heavy operations use callback refs to avoid re-renders:

```typescript
const readyBlobUrlsRef = useRef<Map<string, string>>(new Map());

// O(1) lookup without triggering re-renders
const getBlobUrl = useCallback((url: string) => {
  return readyBlobUrlsRef.current.get(url) || null;
}, []);
```

### 3. Cleanup on Unmount

All hooks properly cleanup resources:

```typescript
useEffect(() => {
  const controller = new AbortController();

  fetchData(controller.signal);

  return () => controller.abort();
}, []);
```

### 4. Memoization

Expensive computations are memoized:

```typescript
const neighbors = useMemo(() => {
  return buildNeighborGraph(pages, pageLinks);
}, [pages, pageLinks]);
```

---

## Hook Composition

Hooks are designed for composition - larger hooks use smaller hooks:

```
RuntimePresentation
├── usePageDataLoader
├── usePreloadOrchestrator
│   └── useNeighborGraph
├── usePageNavigationState     # Unified state machine (replaces 6 hooks)
│   └── Internal: useReducer + derived state via useMemo
├── useTransitionPlayback      # Uses pre-generated reversed videos
└── usePageNavigation          # History tracking
```

```
ConstructorPage
├── usePageDataLoader
├── usePreloadOrchestrator
│   └── useNeighborGraph
├── usePageNavigationState     # Same unified state machine
├── useConstructorElements
├── useCanvasElementDrag
├── useConstructorPageActions
├── useTransitionPreview
├── useDraggable (multiple instances)
└── useOutsideClick
```

**Note:** The `usePageNavigationState` hook consolidated:
- `usePageSwitch` - URL resolution and switching
- `useBackgroundState` - Background ready tracking
- `useBackgroundTransition` - Fade-from-black effects
- `useTransitionCleanup` - Video cleanup coordination
- `useBackgroundUrls` - URL resolution for display
- `pageLoadingUtils` - Loading state computation

---

## Performance Considerations

### 1. Tree-Shaking

Large hooks are imported directly rather than via index.ts:

```typescript
// Good - only imports what's needed
import { usePreloadOrchestrator } from '../hooks/usePreloadOrchestrator';

// Avoid for large hooks
import { usePreloadOrchestrator } from '../hooks';
```

### 2. Ref-Based State

State that doesn't need to trigger re-renders uses refs:

```typescript
// Good - no re-renders
const queueRef = useRef<PriorityQueue>(new PriorityQueue());

// Avoid for high-frequency updates
const [queue, setQueue] = useState<Item[]>([]);
```

### 3. Debounced Updates

High-frequency operations are debounced:

```typescript
const debouncedUpdate = useMemo(
  () => debounce((value) => setPosition(value), 16),
  []
);
```

---

## Testing Considerations

Hooks can be tested with `@testing-library/react-hooks`:

```typescript
import { renderHook, act } from '@testing-library/react-hooks';
import { useFilterItems } from './useFilterItems';

test('adds filter', () => {
  const { result } = renderHook(() => useFilterItems(filters));

  act(() => {
    result.current.addFilter();
  });

  expect(result.current.filterItems).toHaveLength(1);
});
```

---

## Component-Specific Hooks

Some hooks are co-located with their components rather than in the central hooks directory:

### useAssetUploader

**Location:** `frontend/src/components/Assets/useAssetUploader.ts` (~279 LOC)

**Purpose:** Batch asset upload management with queue tracking, concurrent uploads, and MIME validation.

```typescript
interface UseAssetUploaderReturn {
  uploadingSections: string[];                    // Sections with active uploads
  uploadQueues: Record<string, UploadQueueItem[]>; // Per-section upload queues
  runBatchUpload: (section: AssetSection, files: File[]) => Promise<void>;
}
```

**Key Features:**
- Batch upload with queue management (max 2 concurrent)
- Per-file progress tracking
- Abortable uploads via AbortController
- MIME validation via validation schema
- Media duration probing for video/audio

**Validation Integration:**
```typescript
// Passes validation schema to UploadService
const validationSchema = { assetType: section.assetFormat };
const remoteFile = await FileUploader.uploadChunked(
  `assets/${projectId}`,
  file,
  validationSchema,  // Validates MIME type matches asset format
  { onProgress, onStatus, signal }
);
```

See [Asset Upload & Variants](../../documentation/asset-upload-variants.md) for complete upload flow documentation.

---

## Related Documentation

- [Video Hooks Module](./video-hooks-module.md) - Video playback primitive hooks
- [Constructor Page Editor](./constructor-page-editor.md) - Visual tour builder
- [Runtime Presentation](./runtime-presentation.md) - Tour playback viewer
- [Navigation & Smooth Transitions](./navigation-smooth-transitions.md) - Page switching with transitions
- [Frontend Architecture](./frontend-architecture.md) - Overall frontend structure
- [Components Module](./components-module.md) - React components
- [Assets Preloading](../../documentation/assets-preloading.md) - Preloading strategy
- [Asset Upload & Variants](../../documentation/asset-upload-variants.md) - Asset upload pipeline

---

## Summary

| Category | Hooks | Total LOC | Notes |
|----------|-------|-----------|-------|
| Runtime/Preloading | 10 | ~3,274 | Includes `usePageNavigationState` (~520 LOC) |
| Video Hooks (new) | 8 | ~1,270 | New composable video primitives |
| PWA/Offline | 5 | ~1,160 | Unchanged |
| Constructor | 10 | ~2,156 | Uses shared `usePageNavigationState` |
| Table/List | 3 | ~595 | Unchanged |
| Form | 2 | ~274 | Unchanged |
| UI Utility | 10 | ~1,583 | +useAudioEffects (~305 LOC) |
| Query Hooks | 13 | ~1,051 | Unchanged |
| **Total** | **53** | **~10,843** | +8 video hooks, -4 consolidated, +1 audio hook |

**Recent Architecture Changes:**

1. **Page Navigation Consolidation:** 6+ fragmented hooks consolidated into `usePageNavigationState`:
   - Replaced boolean flag combinations with explicit phases
   - Prevented race conditions via atomic `useReducer` transitions
   - Eliminated ~1,100 LOC of duplicated state management

2. **Video Hooks Module:** New `hooks/video/` directory with 8 primitive hooks:
   - Composable primitives for any video playback scenario
   - Used by `useTransitionPlayback`, `useBackgroundVideoPlayback`, `useVideoPlayer`
   - See [Video Hooks Module](./video-hooks-module.md) for details

3. **Preloading Simplification:** Stream-first approach:
   - Removed neighbor graph traversal (`useNeighborGraph` deleted)
   - Only preloads current page + outgoing transition videos
   - Videos stream on-demand, then cache for replay

4. **Flash Fix:** Instant overlay hide with rAF delay:
   - `TransitionPreviewOverlay` uses `requestAnimationFrame` delay before hiding
   - Ensures new background is painted before overlay removed
   - `PreviousBackgroundOverlay` simplified to pure show/hide (no fade)

5. **Audio Effects:** New `useAudioEffects` hook for element sound effects:
   - Plays audio on hover start (completes even after mouse leave)
   - Plays audio on click/active (interruptible, restarts on re-click)
   - Uses authenticated fetch with blob URLs for secure audio access
   - Integrates with `useElementEffects` via exposed `state.isHovered`/`state.isActive`
   - Works in constructor preview mode and runtime presentations

The hooks module provides comprehensive reusable logic that powers the application's core features while maintaining clean separation of concerns and tree-shaking friendly architecture.