docs: add offline sync & PWA documentation

feat: improve PWA resilience with SWR and navigation timeouts

OFFLINE_SYNC_PWA.md

@@ -0,0 +1,91 @@
+# Offline Sync & PWA Architecture Documentation
+
+This document describes the offline capabilities and synchronization mechanism implemented in the Whisky Vault application. It is designed to be easily parsed by both humans and AI agents.
+
+## 🏗️ Architecture Overview
+
+The application uses a **Stale-While-Revalidate (SWR)** pattern for reading data and a **Background Sync Queue** for writing data.
+
+### Technical Stack
+- **Database Engine**: [Dexie.js](https://dexie.org/) (IndexedDB wrapper)
+- **Framework**: Next.js (App Router)
+- **State Management**: `dexie-react-hooks` (`useLiveQuery`)
+- **Backend/Auth**: Supabase
+- **PWA**: Service Worker (`sw.js`) & Web App Manifest
+
+---
+
+## 🗄️ Database Schema (IndexedDB)
+
+The database `WhiskyVault` is defined in `src/lib/db.ts`.
+
+| Table | Indexing | Purpose |
+| :--- | :--- | :--- |
+| `pending_scans` | `++id, temp_id, timestamp` | Stores images (Base64) and metadata of bottles scanned while offline. |
+| `pending_tastings` | `++id, bottle_id, pending_bottle_id` | Stores tasting notes. Can link to a real `bottle_id` or a `pending_bottle_id`. |
+| `cache_tags` | `id, category, name` | Local cache for whisky tags (aroma, flavor, etc.). |
+| `cache_buddies` | `id, name` | Local cache for user's buddies. |
+| `cache_bottles` | `id, name, distillery` | Local cache for bottle details (SWR). |
+| `cache_tastings` | `id, bottle_id, created_at` | Local cache for tasting notes (SWR). |
+
+---
+
+## 🔄 Synchronization Logic
+
+### 1. Reading Data (SWR Pattern)
+Implemented in hooks like `useBottleData`.
+
+```mermaid
+graph TD
+    A[Component Mounts] --> B[useLiveQuery: Get from Dexie]
+    B --> C[UI renders cached data]
+    C --> D{Is Online?}
+    D -- Yes --> E[Fetch from Supabase]
+    E --> F[Update Dexie Table]
+    F --> G[useLiveQuery triggers re-render]
+    D -- No --> H[Keep showing cache]
+```
+
+### 2. Writing Data (Background Sync)
+Implemented in `src/components/UploadQueue.tsx`.
+
+#### The Reconciliation Logic
+A critical feature is the ability to link tasting notes to a bottle that hasn't been synced to the server yet.
+
+1. **Offline Scan**: User takes a photo. It's stored in `pending_scans` with a `temp_id` (UUID).
+2. **Offline Tasting**: User adds a note. It's stored in `pending_tastings` with `pending_bottle_id` set to the scan's `temp_id`.
+3. **Sync Phase 1 (Scans)**: When online, `magicScan` (AI analysis) and `saveBottle` are called. A real `bottle_id` is returned from Supabase.
+4. **Reconciliation**: The code searches `pending_tastings` for all entries matching the `temp_id` and updates them with the real `bottle_id`.
+5. **Sync Phase 2 (Tastings)**: The reconciled tasting notes are then uploaded to Supabase.
+
+---
+
+## 📱 PWA Features
+
+### Service Worker (`public/sw.js`)
+- **Strategy**: Network-First. Attempts to fetch from network, falls back to cache if offline.
+- **Cache Bypassing**: Explicitly bypasses cache for:
+    - `*/auth/*`
+    - `*/api/*`
+    - `*.supabase.co/*`
+- **Asset Caching**: Caches static assets (`manifest.json`, icons) during installation.
+
+### Manifest (`src/app/manifest.ts`)
+Defines the app's appearance when installed:
+- **Display**: `standalone` (removes browser UI)
+- **Theme Color**: `#d97706` (Amber)
+- **Background**: `#000000`
+
+---
+
+## 🛠️ Key Components & Hooks
+
+- `src/lib/db.ts`: Database definition and TypeScript interfaces.
+- `src/hooks/useBottleData.ts`: Example of the SWR pattern implementation.
+- `src/components/UploadQueue.tsx`: The "Sync Engine" UI and logic coordinator.
+- `src/components/PWARegistration.tsx`: Client-side Service Worker registration handler.
+
+## ⚠️ Edge Case Handling
+- **Partial Sync**: If a scan succeeds but a tasting fails, the tasting remains in the queue with the now-valid `bottle_id`.
+- **Duplicate Scans**: The system relies on the user not submitting the same scan multiple times while offline (UI prevents multiple clicks).
+- **Stale Cache**: Caches are overwritten on every successful online fetch to ensure eventual consistency.

public/sw.js

@@ -1,4 +1,4 @@
-const CACHE_NAME = 'whisky-vault-v2'; // Increment version to force update
+const CACHE_NAME = 'whisky-vault-v3'; // Increment version to apply new strategy
 const ASSETS_TO_CACHE = [
     '/manifest.json',
     '/icon-192.png',
@@ -29,6 +29,26 @@ self.addEventListener('activate', (event) => {
     self.clients.claim();
 });
 
+// Helper for Network-First with Timeout
+function fetchWithTimeout(request, timeoutMs = 3000) {
+    return new Promise((resolve, reject) => {
+        const timeoutId = setTimeout(() => {
+            reject(new Error('Network timeout'));
+        }, timeoutMs);
+
+        fetch(request).then(
+            (response) => {
+                clearTimeout(timeoutId);
+                resolve(response);
+            },
+            (err) => {
+                clearTimeout(timeoutId);
+                reject(err);
+            }
+        );
+    });
+}
+
 self.addEventListener('fetch', (event) => {
     const url = new URL(event.request.url);
 
@@ -40,32 +60,47 @@ self.addEventListener('fetch', (event) => {
     const isSupabaseRequest = url.hostname.includes('supabase.co');
 
     if (isAuthRequest || isApiRequest || isSupabaseRequest) {
-        // console.log('[SW] Bypassing cache for:', url.pathname);
         return;
     }
 
-    // Network first for all other requests, especially navigation
+    // 1. ASSETS & APP SHELL: Stale-While-Revalidate
+    const isAsset = event.request.destination === 'style' ||
+        event.request.destination === 'script' ||
+        event.request.destination === 'worker' ||
+        event.request.destination === 'font' ||
+        event.request.destination === 'image' ||
+        url.pathname.startsWith('/_next/static');
+
+    if (isAsset) {
         event.respondWith(
-        fetch(event.request)
+            caches.match(event.request).then((cachedResponse) => {
-            .then((response) => {
+                const fetchPromise = fetch(event.request).then((networkResponse) => {
-                // Optionally cache successful GET requests for assets
+                    if (networkResponse && networkResponse.status === 200) {
-                if (
+                        const responseClone = networkResponse.clone();
-                    event.request.method === 'GET' &&
-                    response.status === 200 &&
-                    (url.pathname.startsWith('/_next/static/') || ASSETS_TO_CACHE.includes(url.pathname))
-                ) {
-                    const responseClone = response.clone();
                         caches.open(CACHE_NAME).then((cache) => {
                             cache.put(event.request, responseClone);
                         });
                     }
-                return response;
+                    return networkResponse;
+                });
+                return cachedResponse || fetchPromise;
             })
-            .catch((err) => {
+        );
-                if (event.request.mode === 'navigate') {
+        return;
-                    console.log('[SW] Navigation failed, attempting cache fallback for:', url.pathname);
     }
+
+    // 2. NAVIGATION: Network-First with 3s Timeout
+    if (event.request.mode === 'navigate') {
+        event.respondWith(
+            fetchWithTimeout(event.request, 3000)
+                .catch(() => {
+                    console.log('[SW] Navigation network failure or timeout, falling back to cache');
                     return caches.match(event.request);
                 })
         );
+        return;
+    }
+
+    // Default: Network-Only or default fetch
+    return;
 });