# Technology Stack

**Project:** Sage (Household Food Inventory Tracker)
**Researched:** 2026-01-27
**Focus:** Completely free, open source, self-hostable with Supabase free tier + optional Docker

## Executive Summary

Sage's tech stack prioritizes cost-free operation, multi-platform reach, and self-hosting capability. Core recommendations: **Supabase** (free tier PostgreSQL + Realtime) as primary backend with optional self-hosted Docker deployment, **Flutter + Riverpod 3.0** for shared mobile/web code, **mobile_scanner** for barcode capture, **Open Food Facts API** for product data (with local caching), and **Hive** for offline inventory caching. This combination keeps both development and operational costs at $0 while providing production-quality infrastructure.

---

## Recommended Stack

### Frontend: Flutter (Android + Web)

| Technology | Version | Purpose | Why |
|------------|---------|---------|-----|
| **Flutter** | 3.24+ | Cross-platform UI framework | Single codebase for Android, iOS, and web. Shared code reduces maintenance burden. Production-ready, widely adopted. |
| **Riverpod 3.0+** | 3.2.0+ (pub.dev) | State management | Compile-time safety, automatic retry on network errors, lowest boilerplate. New Mutations API simplifies write operations (critical for inventory updates). Better than Provider/BLoC for this domain. |
| **mobile_scanner 7.1.4+** | 7.1.4 | Barcode scanning | Lightweight, supports Android/iOS/Web. Uses ML Kit on Android, Vision Kit on iOS, ZXing on web. No dependency on paid SDKs. Supports EAN-13, UPC-A, Code 128 (via underlying ML Kit/VisionKit/ZXing). |
| **Hive 4.0+** | Latest | Local offline cache | Fast encrypted NoSQL storage (~500ms reads vs 8000ms SharedPreferences). Essential for offline inventory viewing when synced from server. AES-256 encryption built-in. |
| **go_router 12+** | Latest | Navigation | Type-safe routing for multi-screen app. Works on all platforms. |

#### Frontend Architecture

```
lib/
├── main.dart
├── providers/           # Riverpod state management
│   ├── auth_provider.dart
│   ├── inventory_provider.dart   # FutureProvider wraps Supabase calls
│   ├── barcode_provider.dart     # Caches barcode lookups
│   └── household_provider.dart   # Multi-user household context
├── screens/            # UI layer
│   ├── inventory/
│   ├── barcode_scan/
│   ├── expiry_alerts/
│   └── shopping/
├── services/           # Business logic
│   ├── supabase_client.dart      # Supabase initialization
│   ├── barcode_service.dart      # Barcode scanning + caching
│   ├── open_food_facts_service.dart
│   └── notification_service.dart
└── models/             # Data classes
    ├── food_item.dart
    ├── household.dart
    └── user.dart
```

**State Management Pattern:**
- Riverpod `FutureProvider` wraps Supabase calls (read-only)
- Riverpod `Notifier` + `NotifierProvider` for mutations (inventory updates, deletions)
- Hive for offline cache of recently-viewed inventory
- Automatic sync when connection restored via Riverpod's automatic retry

### Backend: Supabase (Hosted Free + Optional Self-Hosted)

| Technology | Version | Purpose | Why |
|------------|---------|---------|-----|
| **Supabase** | Latest | Backend-as-a-Service | PostgreSQL (not Firestore) = full relational power for complex queries. Free tier supports 50K MAU and unlimited API calls (critical). Realtime subscriptions included free tier (10K concurrent connections). No per-request billing like Firebase. Self-hosted Docker option available. |
| **PostgreSQL 15+** | Managed by Supabase | Relational database | SQL allows complex joins (households, users, inventory, expiry tracking). ACID transactions for multi-user safety. Row-level security (RLS) built into Supabase. Extensible with triggers/functions. |
| **Supabase Realtime** | Built-in | Multi-device sync | PostgreSQL logical replication → WebSocket broadcasts. Included free. 200 concurrent peak connections on free tier (sufficient for small households). Clients subscribe to table changes. |
| **Supabase Auth** | Built-in | User authentication | Email/password + OAuth ready. Row-level security policies tied to auth context. 50K MAU free. |
| **Supabase Storage** | Built-in | File uploads | 1 GB free. Use for food photos (optional UI feature later). |

**Free Tier Constraints (2026):**
- 500 MB database storage (sufficient for 10K+ food items with metadata)
- 2 GB database egress per month (watch for high-volume syncs)
- 200 concurrent realtime connections peak (one connection per client = 200 simultaneous users)
- **CRITICAL GOTCHA:** Free projects pause after 7 days inactivity. **Mitigation:** Add keep-alive job (GitHub Actions pings API weekly) or self-host. Users cannot avoid this on hosted free tier.
- Limited to 2 active projects (paused projects don't count)

#### Self-Hosted Option (Docker Compose)

For users wanting to avoid inactivity pausing:

```bash
# Clone Supabase repo
git clone https://github.com/supabase/supabase.git
cd supabase/docker

# Configure .env with secure keys (NEVER use defaults)
cp .env.example .env
# Edit .env: Change ANON_KEY, SERVICE_ROLE_KEY, JWT_SECRET

# Start services
docker-compose up -d

# Minimum requirements: 8GB RAM, 25GB SSD
# Remove unused services from docker-compose.yml if needed:
# - Logflare (analytics) - unnecessary
# - imgproxy (image resizing) - unnecessary early
# Keep: postgres, kong (API gateway), auth, realtime, storage
```

**Self-hosted costs:** $0/month software + infrastructure (5-30 EUR/month for basic VPS)

### Database Schema (PostgreSQL)

```sql
-- Multi-tenant: Shared database, shared schema, tenant_id discriminator
-- Simplest approach for self-hosted, scales to thousands of households

CREATE TABLE households (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  name TEXT NOT NULL,
  created_by UUID REFERENCES auth.users(id),
  created_at TIMESTAMP DEFAULT NOW()
);

CREATE TABLE household_members (
  household_id UUID REFERENCES households(id) ON DELETE CASCADE,
  user_id UUID REFERENCES auth.users(id) ON DELETE CASCADE,
  role TEXT DEFAULT 'member', -- 'owner' or 'member'
  joined_at TIMESTAMP DEFAULT NOW(),
  PRIMARY KEY (household_id, user_id)
);

CREATE TABLE food_items (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  household_id UUID NOT NULL REFERENCES households(id) ON DELETE CASCADE,
  name TEXT NOT NULL,
  category TEXT, -- 'produce', 'dairy', 'meat', 'pantry', etc.
  barcode TEXT, -- EAN-13, UPC-A cached from Open Food Facts
  quantity INT DEFAULT 1,
  unit TEXT, -- 'pieces', 'kg', 'liters', 'ml'
  expiry_date DATE,
  location TEXT, -- 'fridge', 'freezer', 'pantry'
  purchase_date DATE,
  product_data JSONB, -- From Open Food Facts (name, brand, nutrition, ingredients)
  added_by UUID REFERENCES auth.users(id),
  created_at TIMESTAMP DEFAULT NOW(),
  updated_at TIMESTAMP DEFAULT NOW()
);

CREATE INDEX idx_food_household_expiry
  ON food_items(household_id, expiry_date);

-- Barcode -> Product cache (avoids repeated API calls)
CREATE TABLE barcode_cache (
  barcode TEXT PRIMARY KEY,
  product_data JSONB, -- Full OFF product info
  cached_at TIMESTAMP DEFAULT NOW(),
  source TEXT -- 'open_food_facts', 'barcode_lookup'
);

-- Expiry alerts log (for notification dedup)
CREATE TABLE expiry_alerts_sent (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  household_id UUID NOT NULL,
  food_item_id UUID NOT NULL,
  alert_type TEXT, -- 'expiring_soon', 'expired'
  sent_at TIMESTAMP DEFAULT NOW(),
  UNIQUE(food_item_id, alert_type, DATE(sent_at))
);

-- Usage history (for shopping list AI predictor)
CREATE TABLE consumption_history (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  household_id UUID NOT NULL,
  food_name TEXT NOT NULL,
  category TEXT,
  quantity_consumed INT,
  consumed_date DATE NOT NULL,
  household_id UUID REFERENCES households(id) ON DELETE CASCADE,
  created_at TIMESTAMP DEFAULT NOW()
);

-- Row-Level Security: Each household only sees their data
ALTER TABLE food_items ENABLE ROW LEVEL SECURITY;

CREATE POLICY "Users can only access their household's items"
  ON food_items
  FOR SELECT
  USING (
    household_id IN (
      SELECT household_id FROM household_members
      WHERE user_id = auth.uid()
    )
  );

CREATE POLICY "Users can modify their household's items"
  ON food_items
  FOR UPDATE
  USING (
    household_id IN (
      SELECT household_id FROM household_members
      WHERE user_id = auth.uid()
    )
  );
```

### Data Sync Architecture

**Realtime sync (Supabase Realtime):**

```dart
// Riverpod provider subscribes to food_items table changes
final inventoryProvider = StreamProvider<List<FoodItem>>((ref) {
  final userId = ref.watch(authProvider).value?.id;
  if (userId == null) return const Stream.empty();

  return supabase
    .from('food_items')
    .stream(primaryKey: ['id'])
    .eq('household_id', currentHouseholdId) // RLS enforces this
    .map((List<dynamic> data) =>
      (data as List).map((item) => FoodItem.fromJson(item)).toList()
    );
});

// UI rebuilds automatically when server sends changes
// Other family members' updates appear in real-time
```

### Barcode Scanning & Product Lookup

| Technology | Version | Purpose | Why |
|------------|---------|---------|-----|
| **mobile_scanner** | 7.1.4+ | Barcode capture | Open source, ML Kit backend, no API costs |
| **Open Food Facts API** | Public | Product database | Free, no auth required. 100 req/min for product lookup. Community-driven. Best nutritional data coverage. |
| **Barcode Lookup / EAN-Search (fallback)** | Free tier | Secondary product source | If OFF doesn't have product. Free lookup available. |

#### Barcode Caching Strategy

**Problem:** Open Food Facts rate limits = 100 req/min for product queries. With household sync, this can be hit quickly if multiple users scan same barcode.

**Solution: Client-side + Server-side cache**

```dart
// Frontend: Hive local cache (checked first)
final barcodeService = BarcodeService();
final cachedProduct = hiveBox.get(barcode);
if (cachedProduct != null && !isStale(cachedProduct)) {
  return cachedProduct; // 0ms, no API call
}

// Server cache: PostgreSQL barcode_cache table (checked second)
final serverCached = await supabase
  .from('barcode_cache')
  .select()
  .eq('barcode', barcode)
  .single();
if (serverCached.exists && isRecent(serverCached)) {
  return serverCached; // Store in Hive for next time
}

// Hit Open Food Facts API (last resort)
final product = await openFoodFactsApi.getProduct(barcode);
// Store in both Hive + PostgreSQL
await hiveBox.put(barcode, product);
await supabase.from('barcode_cache').insert({
  'barcode': barcode,
  'product_data': product.toJson(),
  'source': 'open_food_facts'
});
return product;
```

**Cache invalidation:** 30-day TTL per barcode (products rarely change that fast). Manual refresh available in UI.

### Notifications & Integrations

| Technology | Version | Purpose | Why |
|------------|---------|---------|-----|
| **Supabase Edge Functions** | Built-in | Scheduled jobs | Serverless functions (TypeScript) check expiry dates nightly, trigger alerts. Free tier: 500K invocations/month. |
| **ntfy.sh** | Self-hosted or public | Push notifications | Open source, free. Send to ntfy topics or bridge to Discord/Slack. No infrastructure needed for basic version. |
| **Discord Webhooks** | Native | Optional alert channel | Teams can subscribe household alerts to Discord channel. 0 cost. |

**Expiry Alert Flow:**

```
1. Nightly Edge Function (11 PM)
   → SELECT food_items WHERE expiry_date BETWEEN TODAY AND TODAY+3 DAYS
   → Grouped by household_id

2. For each household:
   → Check dedup table (already alerted today for this item?)
   → If new: send via ntfy.sh OR Discord webhook if configured
   → Log to expiry_alerts_sent table

3. Client receives alert:
   → Notification badge on app
   → If ntfy: push to phone
   → If Discord: posted to channel
```

### Simple AI/ML for Shopping Prediction

| Technology | Purpose | Implementation |
|------------|---------|-----------------|
| **Simple statistical approach** | Predict next purchase date | No heavy ML needed. Use `consumption_history` table. When user marks item consumed, log to table. Riverpod provider computes: frequency = items consumed per month. Next purchase = last_purchase + (30 / frequency). Display on shopping list as "Usually buy X every Y days". |
| **Hive (if expanding)** | Store prediction model coefficients | Not needed initially. Keep in Firebase/Supabase if later adding regression. |

---

## Installation & Setup

### Frontend Setup

```bash
# Create Flutter project
flutter create sage --platforms android,web

cd sage

# Add dependencies
flutter pub add \
  flutter_riverpod:^2.6.0 \
  riverpod_generator:^2.6.0 \
  build_runner:^2.4.0 \
  supabase_flutter:^2.0.0 \
  mobile_scanner:^7.1.4 \
  hive:^2.2.3 \
  hive_flutter:^1.1.0 \
  go_router:^14.0.0

# Dev dependencies
flutter pub add -d \
  riverpod_generator:^2.6.0 \
  build_runner:^2.4.0

# Generate Riverpod code
dart run build_runner watch -d

# Run
flutter run -d android
flutter run -d chrome  # Web
```

### Backend Setup (Supabase Cloud Free Tier)

1. Sign up: https://supabase.com
2. Create project (auto-pauses after 7 days inactivity)
3. Go to SQL Editor → paste schema (see Database Schema above)
4. Enable Row Level Security on all tables
5. In Flutter app:

```dart
// Initialize Supabase
void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Supabase.initialize(
    url: 'https://your-project.supabase.co',
    anonKey: 'your-anon-key', // Safe to commit
  );
  runApp(const MyApp());
}
```

### Backend Setup (Self-Hosted Docker)

```bash
# Clone Supabase
git clone https://github.com/supabase/supabase.git
cd supabase/docker

# Configure
cp .env.example .env
# Edit .env: Set secure JWT_SECRET, ANON_KEY, SERVICE_ROLE_KEY
# Example: Generate keys with: openssl rand -base64 32

# Start
docker-compose up -d

# Access:
# Supabase Studio: http://localhost:3000
# API: http://localhost:8000
# Realtime: ws://localhost:8000
```

---

## Alternatives Considered

| Category | Recommended | Alternative | Why Not Recommended |
|----------|-------------|-------------|-------------------|
| **Backend** | Supabase PostgreSQL | Firebase Firestore | Per-document billing unpredictable with realtime listeners. Firestore doesn't support complex joins needed for household + inventory queries. No self-hosting option. |
| **Backend** | Supabase PostgreSQL | Appwrite | Appwrite self-hosted is free, but requires more infrastructure overhead (Docker Swarm/K8s). Supabase's free tier is more mature. Multi-language function support in Appwrite less relevant for this project. |
| **State Mgmt** | Riverpod 3.0 | BLoC | BLoC more boilerplate, less suitable for shared web/mobile. Riverpod's mutations (new in 3.0) simplify writes. |
| **State Mgmt** | Riverpod 3.0 | Provider | Provider lacks compile-time safety and automatic retry. Riverpod newer, actively developed. |
| **Realtime Sync** | Supabase Realtime | Firebase Realtime DB | Firebase charges per read/listener. Less suitable for multi-tenant. Supabase cheaper at scale. |
| **Local Cache** | Hive | SQLite | SQLite slower for simple K-V. Hive encrypted by default. |
| **Barcode Scanning** | mobile_scanner | flutter_zxing | mobile_scanner uses native APIs (ML Kit/Vision Kit) = more accurate. ZXing pure Dart = slower on mobile. |
| **Barcode Data** | Open Food Facts | Barcode Lookup API | OFF more comprehensive nutritional data. BarcodeAPI requires paid tiers for volume. |

---

## Free Tier Gotchas & Mitigation

### Supabase Hosted Free Tier

**Gotcha 1: Inactivity Pause**
- Projects pause after 7 days without API calls
- Even a static homepage doesn't count (must hit database)
- **Mitigation:**
  - Add GitHub Actions to ping API weekly: `curl https://project.supabase.co/rest/v1/tables`
  - OR use self-hosted Docker (eliminates pausing)

**Gotcha 2: Storage Limit (500 MB)**
- Sufficient for 10K food items with product metadata (JSON)
- NOT sufficient if storing food photos
- **Mitigation:** Defer photos to post-MVP or use S3 integration (paid)

**Gotcha 3: Realtime Concurrent Connections (200 peak)**
- Small households fine, but if scaling to 200+ active households simultaneously = limit reached
- Each browser tab = one connection
- **Mitigation:** Implement connection pooling or move to Pro ($25/month) for 500 connections

**Gotcha 4: Database Egress (5 GB/month)**
- Each byte downloaded from API counts
- Heavy sync + large payloads = rapid consumption
- **Mitigation:** Implement pagination, compress JSON, use partial selects (`select: 'id,name,expiry_date'`)

### Firebase (Not Recommended, Included for Comparison)

**Gotcha 1: Per-Read Billing**
- Listening to query = charged per document in result set
- Small household = 50 items, listener active = 50 reads per update
- At scale: $50+/month easily

**Gotcha 2: One Free Database Per Project**
- Named databases not included in free tier
- Complex queries across databases cost double

---

## Recommended Local Development Workflow

### Development

```bash
# Terminal 1: Supabase Docker (if developing offline)
cd supabase/docker && docker-compose up

# Terminal 2: Flutter
flutter run -d chrome  # Or android emulator

# Terminal 3: Run code gen
dart run build_runner watch -d
```

### Environment Variables

Create `lib/config/secrets.dart` (add to `.gitignore`):

```dart
const String SUPABASE_URL = 'https://your-project.supabase.co';
const String SUPABASE_ANON_KEY = 'your-key';
const String OPEN_FOOD_FACTS_USER_AGENT = 'Sage/1.0';
```

Or use `.env` + `flutter_dotenv` package for easier secrets management.

---

## Version Pinning Strategy

```yaml
# pubspec.yaml
dependencies:
  flutter_riverpod: ^3.2.0    # Use 3.x for mutations
  supabase_flutter: ^2.0.0    # Stable 2.x branch
  mobile_scanner: ^7.1.4      # Latest 7.x
  hive: ^2.2.3
  go_router: ^14.0.0

  # Lock critical versions
  riverpod_generator: 2.6.0   # Exact for code generation consistency
  build_runner: 2.4.0

dev_dependencies:
  flutter_lints: latest
```

Lock `riverpod_generator` to ensure consistent code generation across team.

---

## Sources

### State Management
- [Flutter State Management Options (Official Docs)](https://docs.flutter.dev/data-and-backend/state-mgmt/options)
- [State Management in Flutter: 7 Approaches to Know (2026)](https://www.f22labs.com/blogs/state-management-in-flutter-7-approaches-to-know-2025/)
- [Ultimate Guide to Flutter State Management 2026: Riverpod](https://medium.com/@satishparmarparmar486/the-ultimate-guide-to-flutter-state-management-in-2026-from-setstate-to-bloc-riverpod-561192c31e1c)

### Supabase & Backend
- [Supabase Pricing 2026](https://supabase.com/pricing)
- [Supabase Review 2026: Free Tier Limits & Gotchas](https://hackceleration.com/supabase-review/)
- [Prevent Supabase Free Tier Pausing (2026 Guide)](https://shadhujan.medium.com/how-to-keep-supabase-free-tier-projects-active-d60fd4a17263)
- [Self-Hosting Supabase with Docker](https://supabase.com/docs/guides/self-hosting/docker)
- [Designing Postgres Database for Multi-tenancy](https://www.crunchydata.com/blog/designing-your-postgres-database-for-multi-tenancy)

### Firebase Comparison
- [Firebase vs Supabase for Flutter (2026)](https://medium.com/@mdazadhossain95/firebase-vs-supabase-for-flutter-apps-which-one-should-you-choose-0cf9dd897123)
- [Firestore Quotas and Limits](https://firebase.google.com/docs/firestore/quotas)
- [Firebase Free Tier Gotchas](https://supertokens.com/blog/firebase-pricing)

### Barcode & Product Data
- [Open Food Facts API Documentation](https://openfoodfacts.github.io/openfoodfacts-server/api/)
- [Open Food Facts API Rate Limits](https://openfoodfacts.github.io/documentation/docs/Product-Opener/api/)
- [Mobile Scanner 7.1.4 (pub.dev)](https://pub.dev/packages/mobile_scanner)
- [Popular Flutter Barcode Scanners](https://scanbot.io/blog/popular-open-source-flutter-barcode-scanners/)
- [Barcode Lookup APIs (2026)](https://www.barcodelookup.com/api)

### Local Storage
- [Flutter Local Storage Comparison: Hive vs SharedPreferences (2026)](https://medium.com/@taufik.amary/local-storage-comparison-in-flutter-sharedpreferences-hive-isar-and-objectbox-eb9d9ef9a712)

### Notifications
- [ntfy.sh: Open Source Push Notifications](https://ntfy.sh/)
- [ntfy Integrations & Projects](https://docs.ntfy.sh/integrations/)

---

## Next Steps

1. **Phase 1 (MVP):** Supabase hosted free tier. Add inactivity ping job immediately.
2. **Phase 2+:** Consider self-hosted Docker if inactivity becomes pain point.
3. **Future:** Firebase alternative analysis only if Supabase free tier limits become blocker (unlikely given household scale).
4. **Scaling:** Pro tier ($25/month) if reaching 200+ concurrent households before monetization.