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.