# Technology Stack Decisions

**Last Updated**: 2026-02-14

---

## Decisions Made

### 1. Rust Web Framework: Axum
**Decision**: Axum 0.7.x

**Rationale**:
- Superior I/O performance for encrypted data transfer
- Better streaming support for large encrypted responses
- Lower memory usage for concurrent connections
- Tower middleware ecosystem
- Excellent async patterns for lazy loading

**Reference**: [2026-02-14-performance-findings.md](./2026-02-14-performance-findings.md)

---

### 2. Mobile Framework: React Native
**Decision**: React Native 0.73+ for iOS + Android

**Platform Strategy**:
- **Primary**: Mobile apps (iOS + Android) - Daily health tracking, sensor integration
- **Secondary**: Web browser - Extensive reporting, visualization, profile management

**Rationale**:
- **70-80% code sharing** between mobile and web (single language: TypeScript)
- **Health sensor integration**: react-native-health (HealthKit), react-native-google-fit (Health Connect)
- **QR code scanning**: react-native-camera
- **Encryption**: react-native-quick-crypto (AES-256-GCM, PBKDF2)
- **Web charts**: Recharts for React (beautiful visualizations)
- **Team skills**: Single language (JavaScript/TypeScript) reduces development cost
- **Time to market**: Faster than native or Flutter

**Reference**: [2026-02-14-frontend-mobile-research.md](./2026-02-14-frontend-mobile-research.md)

---

### 3. Web Framework: React
**Decision**: React 18+ for web companion app

**Rationale**:
- **70-80% code sharing** with React Native (business logic, state, API, encryption)
- **Charts**: Recharts for beautiful health data visualizations
- **Ecosystem**: Largest npm ecosystem
- **Team skills**: Single language (TypeScript)

---

### 4. State Management: Redux Toolkit
**Decision**: Redux Toolkit 2.x for React Native + React

**Score**: 9.2/10

**Rationale**:
- **Best for complex state**: Family structure, multi-person profiles, permissions
- **Built-in normalization**: createEntityAdapter for efficient data management
- **Best for offline sync**: RTK Query for server state, optimistic updates, background sync
- **Largest ecosystem**: Most resources, tutorials, examples, production deployments
- **Best developer experience**: Time-travel debugging, predictable state updates
- **TypeScript**: Excellent support, full type safety
- **Code sharing**: 100% between React Native and React

**Trade-offs**:
- More boilerplate: More code, but clearer structure
- Steeper learning curve: More concepts, but better patterns
- Larger bundle: 60KB vs 3KB (negligible impact on 50-100MB app)

**Reference**: [2026-02-14-state-management-research.md](./2026-02-14-state-management-research.md)

---

### 5. Authentication: JWT with Refresh Tokens
**Decision**: JWT (JSON Web Tokens) with Refresh Tokens + Recovery Phrases

**Score**: 9.5/10

**Rationale**:
- **Stateless design**: Scales to 1000+ concurrent connections (no session storage)
- **Mobile-friendly**: Works perfectly with React Native (AsyncStorage)
- **Zero-knowledge compatible**: Integrates with recovery phrases from encryption.md
- **Token revocation**: Refresh token blacklist (MongoDB) + token versioning
- **Token rotation**: Prevents reuse of stolen refresh tokens
- **Family access control**: Permissions in JWT claims (parent, child, elderly)
- **Security best practices**: Short-lived access tokens (15 min), long-lived refresh tokens (30 days)

**Trade-offs**:
- Revocation requires storage (MongoDB for refresh tokens, optional Redis for access tokens)
- More complex than sessions (but better for scaling)

**Reference**: [2026-02-14-jwt-authentication-research.md](./2026-02-14-jwt-authentication-research.md)

---

### 6. Database: MongoDB with Zero-Knowledge Encryption
**Decision**: MongoDB 6.0+ with client-side encryption (ALL sensitive data + metadata)

**Score**: 9.8/10

**Core Principle**: **ALL sensitive data AND metadata must be encrypted client-side before reaching MongoDB**

**Example: Blood Pressure Reading**:
```javascript
// Before encryption (client-side)
{
  value: "120/80",
  type: "blood_pressure",
  unit: "mmHg",
  date: "2026-02-14T10:30:00Z"
}

// After encryption (stored in MongoDB)
{
  healthDataId: "health-123",
  userId: "user-456",
  profileId: "profile-789",
  
  // Encrypted (value + metadata)
  healthData: [
    {
      encrypted: true,
      data: "a1b2c3d4...",
      iv: "e5f6g7h8...",
      authTag: "i9j0k1l2..."
    }
  ]
}
```

**Rationale**:
- **Zero-knowledge**: Server NEVER decrypts data
- **Metadata encryption**: Health data type, unit, doctor, lab ALL encrypted
- **Privacy-preserving**: No plaintext metadata leaks
- **Client-side encryption**: AES-256-GCM, PBKDF2 key derivation
- **Plaintext queries**: Query by userId, profileId, familyId, date, tags
- **Tagging system**: Client adds searchable tags for encrypted data
- **Flexible schema**: MongoDB document structure fits health data
- **Scalable**: Horizontal scaling with sharding

**Collections**:
- **users**: Authentication, profiles, family relationships
- **families**: Family structure, encrypted family name/metadata
- **profiles**: Person profiles, encrypted profile name/metadata
- **health_data**: Encrypted health records (value + metadata)
- **lab_results**: Encrypted lab data (value + metadata)
- **medications**: Encrypted medication data + reminders
- **appointments**: Encrypted appointment data + reminders
- **shares**: Time-limited access to shared data
- **refresh_tokens**: JWT refresh token storage

**What Must Be Encrypted**:
- ✅ Health data values (e.g., "120/80")
- ✅ Health data metadata (e.g., "blood_pressure", "mmHg")
- ✅ Lab test results (e.g., "cholesterol", "200", "LabCorp")
- ✅ Medication data (e.g., "Aspirin", "100mg", "daily")
- ✅ Appointment data (e.g., "checkup", "Dr. Smith")
- ✅ Profile data (e.g., "John Doe", "1990-01-01")
- ✅ Family data (e.g., "Smith Family", "123 Main St")

**What Can Be Plaintext**:
- ✅ User IDs (userId, profileId, familyId) - for queries
- ✅ Email addresses - for authentication
- ✅ Dates (createdAt, updatedAt) - for sorting
- ✅ Data sources (healthKit, googleFit) - for analytics
- ✅ Tags (cardio, daily) - for client-side search

**Reference**: [2026-02-14-mongodb-schema-design-research.md](./2026-02-14-mongodb-schema-design-research.md)

---

## Technology Stack Summary

### Backend
- **Framework**: Axum 0.7.x
- **Runtime**: Tokio 1.x
- **Middleware**: Tower, Tower-HTTP
- **Authentication**: JWT with refresh tokens
- **Database**: MongoDB 6.0+ (with zero-knowledge encryption)
- **Language**: Rust

### Mobile (iOS + Android)
- **Framework**: React Native 0.73+
- **Language**: TypeScript
- **State Management**: Redux Toolkit 2.x
- **Data Fetching**: RTK Query 2.x
- **Authentication**: JWT with AsyncStorage
- **Navigation**: React Navigation
- **Health Sensors**: 
  - react-native-health (iOS HealthKit)
  - react-native-google-fit (Android Health Connect)
- **QR Scanning**: react-native-camera
- **Encryption**: react-native-quick-crypto
- **Persistence**: Redux Persist 6.x (AsyncStorage)
- **HTTP**: Axios

### Web
- **Framework**: React 18+
- **Language**: TypeScript
- **State Management**: Redux Toolkit 2.x
- **Data Fetching**: RTK Query 2.x
- **Authentication**: JWT with localStorage (or httpOnly cookies)
- **Routing**: React Router
- **Charts**: Recharts
- **Persistence**: Redux Persist 6.x (localStorage)
- **HTTP**: Axios

### Shared (Monorepo)
- **Language**: TypeScript
- **State Management**: Redux Toolkit 2.x
- **Reducers**: Shared reducers (user, family, encryption)
- **Selectors**: Shared selectors (Reselect 5.x)
- **API**: Axios
- **Encryption**: AES-256-GCM, PBKDF2
- **Validation**: Zod
- **Date**: date-fns
- **Utilities**: Shared package

---

## All Major Decisions Complete ✅

1. ✅ Rust Framework: Axum 0.7.x
2. ✅ Mobile Framework: React Native 0.73+
3. ✅ Web Framework: React 18+
4. ✅ State Management: Redux Toolkit 2.x
5. ✅ Authentication: JWT with refresh tokens
6. ✅ Database: MongoDB 6.0+ with zero-knowledge encryption

---

## Implementation Phases

- **Phase 1: Research** (COMPLETE)
  - Rust framework selection
  - Mobile/web framework selection
  - State management selection
  - Authentication design
  - Database schema design

- **Phase 2: Backend Development** (NEXT)
  - Axum server setup
  - MongoDB connection
  - JWT authentication
  - CRUD API endpoints
  - Zero-knowledge encryption (client-side)

- **Phase 3: Mobile Development** (AFTER BACKEND)
  - React Native app setup
  - Redux Toolkit setup
  - JWT authentication
  - Health sensor integration
  - QR code scanning
  - Encryption implementation

- **Phase 4: Web Development** (PARALLEL WITH MOBILE)
  - React app setup
  - Redux Toolkit setup
  - JWT authentication
  - Charts and visualizations
  - Profile management
  - Encryption implementation

---

## Next Steps

1. **Backend Development** (Axum + MongoDB)
   - Create Axum server
   - Setup MongoDB connection
   - Implement JWT authentication
   - Create MongoDB indexes
   - Implement CRUD endpoints

2. **Client-Side Encryption** (React Native + React)
   - Implement AES-256-GCM encryption
   - Implement PBKDF2 key derivation
   - Create encryption utilities
   - Test encryption flow

3. **API Development** (Axum)
   - Users API (register, login, logout)
   - Families API (create, update, delete)
   - Profiles API (CRUD)
   - Health Data API (CRUD)
   - Lab Results API (import via QR)
   - Medications API (reminders)
   - Appointments API (reminders)
   - Shares API (time-limited access)

---

## Timeline Estimate

- **Phase 1: Research** (COMPLETE)
- **Phase 2: Backend Development** (8-10 weeks)
- **Phase 3: Mobile Development** (8-12 weeks)
- **Phase 4: Web Development** (4-6 weeks)
- **Phase 5: Testing & Polish** (4-6 weeks)

**Total**: 24-34 weeks (6-8.5 months)

---

## References

- [Axum Performance Research](./2026-02-14-performance-findings.md)
- [Frontend Mobile Research](./2026-02-14-frontend-mobile-research.md)
- [State Management Research](./2026-02-14-state-management-research.md)
- [JWT Authentication Research](./2026-02-14-jwt-authentication-research.md)
- [MongoDB Schema Design](./2026-02-14-mongodb-schema-design-research.md)
- [Normogen Encryption Guide](../encryption.md)
- [Project Introduction](../introduction.md)
