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🏗️ System Design Decisions

Overview​

This document records key architectural decisions made during the development of Valet-in-a-Box, including the rationale and trade-offs for each decision.

ADR-001: Firebase as Primary Backend​

Status: Accepted
Date: 2024-01-15

Context​

We needed to choose a backend platform that could handle real-time updates, authentication, and scalable data storage for a valet management system.

Decision​

We chose Firebase as our primary backend platform, including:

  • Firestore: NoSQL database for real-time data
  • Firebase Auth: User authentication and authorization
  • Firebase Functions: Serverless backend functions
  • Firebase Hosting: Static site hosting with CDN

Rationale​

  • Real-time capabilities: Firestore provides built-in real-time synchronization
  • Authentication: Firebase Auth handles complex auth flows out of the box
  • Scalability: Serverless functions auto-scale based on demand
  • Developer experience: Excellent tooling and documentation
  • Cost efficiency: Pay-per-use pricing model

Trade-offs​

  • Vendor lock-in: Heavy dependence on Google's platform
  • NoSQL limitations: Less structured than SQL databases
  • Cold starts: Function cold starts can impact performance
  • Limited customization: Less control over infrastructure

ADR-002: React with TypeScript Frontend​

Status: Accepted
Date: 2024-01-20

Context​

We needed a modern, maintainable frontend framework that could handle complex state management and real-time updates.

Decision​

We chose React 19 with TypeScript for the frontend, using:

  • React 19: Latest React features and performance improvements
  • TypeScript: Type safety and better developer experience
  • Material-UI: Component library for consistent design
  • React Router: Client-side routing
  • Vite: Fast build tool and dev server

Rationale​

  • Type safety: TypeScript prevents runtime errors and improves maintainability
  • Component reusability: React's component model fits our needs
  • Ecosystem: Large ecosystem of libraries and tools
  • Performance: React 19's concurrent features improve user experience
  • Developer experience: Excellent tooling and debugging capabilities

Trade-offs​

  • Bundle size: Larger initial bundle compared to vanilla JS
  • Learning curve: Team needs to learn React and TypeScript
  • Complexity: More complex than simple HTML/CSS/JS
  • Dependencies: Reliance on many third-party packages

ADR-003: Stripe for Payment Processing​

Status: Accepted
Date: 2024-02-01

Context​

We needed a secure, reliable payment processing solution that could handle various payment methods and international transactions.

Decision​

We chose Stripe as our payment processor with:

  • Stripe Elements: Secure payment form components
  • Payment Intents: Server-side payment processing
  • Webhooks: Real-time payment status updates
  • Stripe Dashboard: Payment management and analytics

Rationale​

  • Security: PCI compliance handled by Stripe
  • Developer experience: Excellent API and documentation
  • Feature completeness: Supports all major payment methods
  • Reliability: 99.9% uptime SLA
  • International support: Global payment processing

Trade-offs​

  • Cost: Transaction fees (2.9% + $0.30)
  • Vendor dependency: Heavy reliance on Stripe's platform
  • Complexity: Requires understanding of payment flows
  • Compliance: Must follow Stripe's terms and guidelines

ADR-004: Twilio for SMS Messaging​

Status: Accepted
Date: 2024-02-10

Context​

We needed a reliable SMS service for customer notifications and status updates.

Decision​

We chose Twilio for SMS messaging with:

  • Twilio API: Programmatic SMS sending
  • Webhooks: Delivery status tracking
  • Phone number validation: E.164 format support
  • Template system: Dynamic message templates

Rationale​

  • Reliability: 99.95% uptime SLA
  • Global reach: Worldwide SMS delivery
  • Developer experience: Simple API and good documentation
  • Delivery tracking: Real-time delivery status updates
  • Cost effective: Competitive pricing for SMS

Trade-offs​

  • Cost: Per-message pricing
  • Rate limits: API rate limiting constraints
  • Vendor dependency: Reliance on Twilio's service
  • Message length: 160 character limit for SMS

ADR-005: Material-UI Component Library​

Status: Accepted
Date: 2024-02-15

Context​

We needed a comprehensive UI component library that would provide consistent design and reduce development time.

Decision​

We chose Material-UI (MUI) v6 as our component library with:

  • Component system: Pre-built, accessible components
  • Theme system: Consistent design tokens
  • Responsive design: Mobile-first approach
  • Accessibility: WCAG compliance built-in

Rationale​

  • Design consistency: Unified look and feel across the application
  • Accessibility: Built-in accessibility features
  • Responsive: Mobile-optimized components
  • Documentation: Excellent documentation and examples
  • Customization: Flexible theming system

Trade-offs​

  • Bundle size: Large component library increases bundle size
  • Design constraints: Limited to Material Design principles
  • Learning curve: Team needs to learn MUI patterns
  • Customization complexity: Some custom designs require workarounds

ADR-006: Firestore Security Rules​

Status: Accepted
Date: 2024-02-20

Context​

We needed to implement security at the database level to prevent unauthorized access to sensitive data.

Decision​

We implemented comprehensive Firestore security rules with:

  • Role-based access: Different permissions for different user roles
  • Field-level security: Protect sensitive fields like payment data
  • Validation rules: Server-side data validation
  • Audit logging: Track all database access

Rationale​

  • Security: Prevents unauthorized data access
  • Performance: Rules are evaluated client-side for speed
  • Flexibility: Fine-grained permission control
  • Maintainability: Centralized security logic

Trade-offs​

  • Complexity: Complex rule logic can be difficult to debug
  • Performance: Complex rules can impact query performance
  • Testing: Security rules are difficult to test thoroughly
  • Maintenance: Rules need to be updated as features change

ADR-007: Real-time Updates with Firestore Listeners​

Status: Accepted
Date: 2024-02-25

Context​

We needed real-time updates for visit status changes, payment updates, and employee notifications.

Decision​

We implemented real-time updates using Firestore listeners with:

  • Real-time listeners: Automatic UI updates when data changes
  • Optimistic updates: Immediate UI feedback for better UX
  • Connection management: Proper cleanup of listeners
  • Error handling: Graceful handling of connection issues

Rationale​

  • User experience: Immediate feedback and updates
  • Efficiency: No need for polling or manual refresh
  • Scalability: Handles multiple concurrent users
  • Simplicity: Built-in real-time capabilities

Trade-offs​

  • Cost: Real-time listeners consume more resources
  • Complexity: Managing listener lifecycle and cleanup
  • Network dependency: Requires stable internet connection
  • Debugging: Real-time updates can be harder to debug

ADR-008: Serverless Architecture​

Status: Accepted
Date: 2024-03-01

Context​

We needed a scalable, cost-effective architecture that could handle varying loads without manual infrastructure management.

Decision​

We adopted a serverless architecture with:

  • Firebase Functions: Serverless backend functions
  • Firebase Hosting: Static site hosting
  • Cloud Run: Containerized Python services
  • Auto-scaling: Automatic scaling based on demand

Rationale​

  • Cost efficiency: Pay only for what you use
  • Scalability: Automatic scaling without manual intervention
  • Maintenance: Reduced infrastructure management
  • Performance: Global edge distribution

Trade-offs​

  • Cold starts: Function cold starts can impact performance
  • Vendor lock-in: Heavy dependence on cloud providers
  • Debugging: More complex debugging in serverless environments
  • Local development: More complex local development setup

ADR-009: TypeScript Strict Mode​

Status: Accepted
Date: 2024-03-05

Context​

We needed to improve code quality and catch errors early in the development process.

Decision​

We enabled TypeScript strict mode with:

  • Strict null checks: Prevent null/undefined errors
  • Strict function types: Ensure function type safety
  • No implicit any: Require explicit type annotations
  • Strict property initialization: Ensure all properties are initialized

Rationale​

  • Error prevention: Catch errors at compile time
  • Code quality: Enforce better coding practices
  • Maintainability: Easier to refactor and maintain code
  • Developer experience: Better IDE support and autocomplete

Trade-offs​

  • Development time: More time spent on type annotations
  • Learning curve: Team needs to understand TypeScript
  • Migration effort: Existing code needs to be updated
  • Build complexity: More complex build process

ADR-010: Comprehensive Testing Strategy​

Status: Accepted
Date: 2024-03-10

Context​

We needed a robust testing strategy to ensure code quality and prevent regressions.

Decision​

We implemented a comprehensive testing strategy with:

  • Unit tests: Jest for functions, Vitest for frontend
  • Integration tests: API endpoint testing
  • E2E tests: Critical user workflow testing
  • Coverage requirements: 80%+ coverage for critical paths

Rationale​

  • Quality assurance: Catch bugs before production
  • Refactoring confidence: Safe to refactor with test coverage
  • Documentation: Tests serve as living documentation
  • Regression prevention: Prevent breaking changes

Trade-offs​

  • Development time: More time spent writing tests
  • Maintenance: Tests need to be maintained alongside code
  • Complexity: More complex development workflow
  • False positives: Tests can fail due to environment issues

These decisions shape the foundation of our platform and guide future development! 🏗️