Technical Constraints & Requirements

# Technical Constraints & Requirements

This document defines the technical constraints, requirements, and architecture decisions for the Scottish Mountain Weather App development.

## Platform & Compatibility Requirements

### Mobile Platform Support

**iOS Requirements:**
- **Minimum Version:** iOS 13.0+ (covers 95% of active users)
- **Target Devices:** iPhone 8 and newer, iPad Air 2 and newer
- **Development:** Swift 5.0+ with UIKit/SwiftUI hybrid approach
- **Distribution:** Apple App Store with TestFlight for beta testing
- **Features:** Background app refresh, push notifications, Core Location

**Android Requirements:**
- **Minimum Version:** Android 8.0 (API level 26+) (covers 87% of active users)
- **Target Devices:** 3GB+ RAM, screens 4.7"-6.9"
- **Development:** Kotlin with Jetpack Compose for modern UI
- **Distribution:** Google Play Store with internal testing track
- **Features:** Foreground services, FCM notifications, Location Services

**Progressive Web App (PWA):**
- **Browsers:** Chrome 80+, Safari 13+, Firefox 75+, Edge 80+
- **Features:** Service Worker for offline, Web App Manifest
- **Limitations:** No background sync, limited push notification support on iOS
- **Use Case:** Fallback for users who prefer web access

### Cross-Platform Framework Decision

**Recommendation: Native Development**
- **Rationale:** Weather apps require optimal performance and platform-specific features
- **iOS:** Swift/SwiftUI for modern declarative UI
- **Android:** Kotlin/Jetpack Compose for performance and modern architecture
- **Shared:** REST API backend, common design system principles

**Alternative Considered: React Native**
- **Pros:** Faster development, shared codebase
- **Cons:** Performance concerns for real-time weather data, platform-specific features complexity
- **Decision:** Not recommended for v1.0 due to performance requirements

## Performance Requirements

### Application Performance

**Launch Time:**
- **Cold start:** <2 seconds on iPhone 8/Galaxy S9 equivalent
- **Warm start:** <1 second
- **First meaningful paint:** <1.5 seconds
- **Time to interactive:** <3 seconds

**Runtime Performance:**
- **Memory usage:** <150MB for active use
- **CPU usage:** <20% during normal operation
- **Battery drain:** <5% per hour of active use
- **Scroll performance:** 60fps minimum, targeting 120fps on capable devices

**Network Performance:**
- **API calls:** <500ms response time for weather data
- **Image loading:** Progressive loading with placeholders
- **Offline capability:** Core functionality available for 24 hours
- **Data usage:** <1MB per weather check, <5MB per session

### Backend Performance

**API Response Times:**
- **Location search:** <200ms (95th percentile)
- **Weather data:** <500ms (95th percentile)
- **Weather comparison:** <800ms (95th percentile)
- **Health check:** <50ms (99th percentile)

**Scalability Requirements:**
- **Concurrent users:** 1,000+ simultaneous API requests
- **Daily requests:** 100,000+ API calls
- **Data throughput:** 10GB+ daily weather data processing
- **Uptime:** 99.5% availability (4.38 hours downtime/month)

## Technical Architecture Constraints

### Backend Technology Stack

**Primary Stack (Recommended):**
```
Backend Framework: FastAPI (Python 3.9+)
Database: PostgreSQL 13+ with TimescaleDB extension
Cache: Redis 6.0+
Message Queue: Celery with Redis broker
Monitoring: Prometheus + Grafana
Logging: Structured JSON logging with ELK stack
```

**Rationale:**
- **FastAPI:** High performance, automatic API documentation, async support
- **PostgreSQL + TimescaleDB:** Excellent time-series data handling for weather
- **Redis:** High-performance caching and session storage
- **Python:** Leverage existing weather_scraper.py codebase

**Alternative Stack (if Python constraints exist):**
```
Backend Framework: Node.js with Express/Fastify
Database: PostgreSQL with time-series optimizations
Cache: Redis
Message Queue: Bull (Redis-based)
```

### Infrastructure Requirements

**Cloud Platform (Recommended: AWS):**
```
Compute: ECS Fargate containers
Database: RDS PostgreSQL with read replicas
Cache: ElastiCache Redis cluster
Storage: S3 for static assets and backups
CDN: CloudFront for global distribution
Load Balancer: ALB with health checks
```

**Alternative: Google Cloud Platform:**
```
Compute: Cloud Run containers
Database: Cloud SQL PostgreSQL
Cache: Memorystore for Redis
Storage: Cloud Storage
CDN: Cloud CDN
Load Balancer: Cloud Load Balancing
```

**Infrastructure Constraints:**
- **Region:** EU-West (Ireland) for GDPR compliance
- **Backup:** Daily automated backups with 30-day retention
- **Disaster Recovery:** Cross-AZ deployment, <4 hour RTO
- **Security:** VPC isolation, WAF protection, DDoS mitigation

### Data Storage Requirements

**Weather Data Volume Estimates:**
- **Locations:** ~500 Scottish mountains
- **Updates:** 4 times daily per location
- **Data retention:** 2 years of historical data
- **Growth rate:** ~100MB/month new data
- **Total storage:** ~5GB database, ~20GB with indexes and backups

**Database Schema Constraints:**
- **Weather data:** Time-series optimized (TimescaleDB hypertables)
- **Location data:** Spatial indexes for proximity queries
- **User data:** Minimal storage, encrypted preferences only
- **Backups:** Point-in-time recovery capability

## Security & Privacy Constraints

### Data Protection Requirements

**GDPR Compliance (EU Users):**
- **Data minimization:** Collect only necessary data
- **Consent management:** Clear opt-in for location services
- **Right to erasure:** Delete user data on request
- **Data portability:** Export user preferences in JSON format
- **Privacy by design:** Default to most private settings

**Data Encryption:**
- **In transit:** TLS 1.3 for all API communications
- **At rest:** AES-256 encryption for sensitive data
- **Keys:** AWS KMS or equivalent key management
- **Certificates:** Let's Encrypt with automatic renewal

**Authentication & Authorization:**
- **API security:** JWT tokens with short expiration
- **Rate limiting:** Prevent abuse and DoS attacks
- **Input validation:** Sanitize all user inputs
- **SQL injection:** Parameterized queries only

### Privacy Constraints

**Location Data:**
- **Permission:** Explicit user consent required
- **Usage:** Only for nearby location suggestions
- **Storage:** No persistent location history
- **Sharing:** Never shared with third parties

**Analytics & Monitoring:**
- **Personal data:** No collection of personal identifiers
- **Usage tracking:** Anonymized analytics only
- **Error reporting:** Crash logs without personal data
- **Compliance:** Privacy-focused analytics (e.g., Plausible vs Google Analytics)

## Integration Constraints

### Weather Data Sources

**Existing System Integration:**
- **weather_scraper.py:** Enhance existing Python scraper
- **YAML config:** Maintain current configuration system
- **Data format:** Compatible with existing JSON output
- **Scheduling:** Keep current 4-hour update cycle

**External API Constraints:**
- **MWIS:** Free service, no API key, rate limiting unknown
- **Met Office:** DataPoint API, requires registration, 5000 calls/day free
- **Mountain-Forecast.com:** No official API, scraping only
- **OpenWeatherMap:** Current integration maintained

**Data Quality Requirements:**
- **Accuracy target:** >85% forecast accuracy vs actual conditions
- **Freshness:** Maximum 6 hours for safety-critical data
- **Reliability:** Graceful degradation when sources unavailable
- **Validation:** Cross-source consistency checking

### Third-Party Service Constraints

**Maps & Location:**
- **iOS:** MapKit for maps, Core Location for GPS
- **Android:** Google Maps API (requires billing), Android Location Services
- **Web:** Mapbox GL JS (free tier available)
- **Offline:** Cache map tiles for essential mountain areas

**Push Notifications:**
- **iOS:** Apple Push Notification Service (APNs)
- **Android:** Firebase Cloud Messaging (FCM)
- **Constraints:** iOS requires annual developer program ($99/year)

**Crash Reporting & Analytics:**
- **Options:** Sentry (error tracking), Mixpanel (privacy-focused analytics)
- **Requirements:** GDPR compliant, minimal data collection
- **Budget:** <$100/month for production usage

## Development Constraints

### Team & Resource Constraints

**Development Team Requirements:**
- **Full-stack developer:** Python/FastAPI backend experience
- **iOS developer:** Swift/SwiftUI experience required
- **Android developer:** Kotlin/Jetpack Compose preferred
- **DevOps engineer:** AWS/Docker experience for deployment
- **Designer:** Mobile UI/UX with accessibility experience

**Timeline Constraints:**
- **MVP deadline:** 16 weeks from start
- **Beta testing:** 2 weeks before public launch
- **App store approval:** Allow 2-4 weeks for review process
- **Seasonal factor:** Launch before winter season (September) preferred

**Budget Constraints:**
- **Infrastructure:** $200-500/month initial costs
- **Third-party services:** $100-300/month
- **App store fees:** $99/year iOS, $25 one-time Android
- **SSL certificates:** Free (Let's Encrypt)
- **Total monthly operational cost:** <$1000

### Development Environment

**Code Repository:**
- **Git hosting:** GitHub with private repositories
- **Branching:** GitFlow with feature branches
- **CI/CD:** GitHub Actions for automated testing and deployment
- **Code quality:** ESLint/SwiftLint, automated testing required

**Testing Requirements:**
- **Unit tests:** >80% code coverage
- **Integration tests:** Critical user flows covered
- **Performance tests:** API response time validation
- **Device testing:** Physical devices for both iOS and Android
- **Accessibility testing:** VoiceOver and TalkBack compatibility

## Deployment & Operations Constraints

### Deployment Strategy

**Backend Deployment:**
- **Containerization:** Docker containers for consistency
- **Orchestration:** ECS Fargate or Google Cloud Run
- **Blue-green deployment:** Zero-downtime updates
- **Database migrations:** Automated with rollback capability

**Mobile App Deployment:**
- **iOS:** TestFlight beta → App Store review → Production
- **Android:** Internal testing → Open testing → Production
- **Feature flags:** Gradual rollout capability
- **Update strategy:** Forced updates for critical security fixes

### Monitoring & Alerting

**Application Monitoring:**
- **Uptime:** External monitoring (UptimeRobot or similar)
- **Performance:** APM with response time tracking
- **Errors:** Real-time error alerting with Sentry
- **Logs:** Centralized logging with search capability

**Business Metrics:**
- **User engagement:** Daily/monthly active users
- **App performance:** Crash rates, load times
- **Weather accuracy:** Forecast vs actual condition tracking
- **API usage:** Request patterns and error rates

## Compliance & Legal Constraints

### App Store Requirements

**iOS App Store:**
- **Content guidelines:** Weather apps generally approved
- **Technical requirements:** 64-bit support, privacy labels
- **Metadata:** Accurate description, appropriate age rating
- **Review time:** 24-48 hours typical, up to 7 days possible

**Google Play Store:**
- **Policy compliance:** Data safety section required
- **Target API:** Must target recent Android API levels
- **Content rating:** PEGI/ESRB rating for content
- **Review time:** Usually within 24 hours

### Accessibility Requirements

**Legal Compliance:**
- **UK:** Equality Act 2010 compliance
- **EU:** EN 301 549 standard
- **US:** Section 508 for government users
- **International:** WCAG 2.1 AA standard

**Technical Implementation:**
- **Screen readers:** VoiceOver (iOS) and TalkBack (Android) support
- **Color contrast:** 4.5:1 minimum ratio
- **Text size:** Dynamic type support
- **Motor accessibility:** 44pt minimum touch targets

## Risk Mitigation

### Technical Risks

**Data Source Reliability:**
- **Risk:** Weather sources become unavailable
- **Mitigation:** Multiple backup sources, graceful degradation
- **Monitoring:** Automated source health checking

**Performance Degradation:**
- **Risk:** App becomes slow under load
- **Mitigation:** Performance testing, auto-scaling infrastructure
- **Monitoring:** Real-time performance metrics

**Security Vulnerabilities:**
- **Risk:** Data breaches or service attacks
- **Mitigation:** Security audit, penetration testing, monitoring
- **Response:** Incident response plan, security patches

### Operational Risks

**App Store Rejection:**
- **Risk:** Apps rejected for policy violations
- **Mitigation:** Follow guidelines strictly, test submission process
- **Contingency:** PWA fallback option

**GDPR Violations:**
- **Risk:** Privacy law non-compliance
- **Mitigation:** Privacy by design, legal review
- **Monitoring:** Data processing audit trail

This technical specification provides a comprehensive foundation for development while acknowledging real-world constraints and limitations.