# Know Foolery - Application Architecture Documentation

## Application Architecture Overview

Know Foolery follows a microservices architecture with clear separation between frontend presentation, backend services, and data persistence layers. The system is designed for cross-platform compatibility, scalability, and maintainability.

### Frontend Architecture
- **Web Application**: Responsive web application
- **Mobile Applications**: Cross platform application for iOS and Android
- **Desktop Applications**: Cross platform application for MacOS, Windows and Linux. Packages the web application 

### Backend Architecture
- **Business Logic**: Domain Driven Design approach 
- **Microservices**: Services with clear domain boundaries
- **API Gateway**: Centralized routing, authentication, and rate limiting
- **Database ORM**: For type-safe database operations
- **Communication**: gRPC for inter-service synchronous communication 
- **External APIs**: Repository pattern for external integrations

### External Services
- **Authentication**: OAuth 2.0/OIDC authentication
- **Relational Database**: For production application data
- **Cache**: Session state and caching layer


## Application Design

### Microservices Design

1. **Game Session Service**: 
  - Responsibilities: Session management, pick next question (excluding already answered), scoring logic, attempts tracking, enforce timer, anti-cheat checks.
  - Scaling driver: concurrent players, realtime updates.
  - Interfaces:
    - Commands: 
      - POST /sessions/start          → Start new game session for a player (user)
      - POST /sessions/end            → End game session
      - POST /sessions/{id}/answer    → Submit answer
      - POST /sessions/{id}/hint      → Request hint
    - Queries
      - GET  /sessions/{id}           → Get session details, including status and timer
      - GET  /sessions/{id}/question  → Get the current question for the session
  - Domain driven design:
    - **Aggregates**: GameSession 
    - **Value Objects**: Attempt, Score 
    - **Domain Services**: Scoring
  - Storage: 
    - Core entities:
      - **Sessions**: id, id of user, score, start_time, end_time, is_active
      - **Session_Questions**: id, id of question
      - **Attempts**: id, id of Session_Questions, answer, score
    - Data relationships : Sessions track multiple question attempts for a user

2. **Question Bank Service**: 
  - Responsibilities: CRUD operations for questions, themes, hints, random selection API with filters (and “exclude these ids”).
  - Scaling driver: editorial ops, cacheable reads.
  - Interfaces:
    - Commands: 
      - POST /questions/random?theme=… with body {exclude:[ids]} → returns 1 random question    
    - Queries
      - GET  /questions/{id} → Get specific question
    - Admin: 
      - POST /admin/questions → Create question
      - PUT /admin/questions/{id} → Update question
      - DELETE /admin/questions/{id} → Delete question
      - GET /admin/themes → List available themes
      - GET /admin/themes/{id}/questions → List all questions for a theme
      - POST /admin/questions/bulk → Bulk question import
  - Domain driven design:
    - **Aggregates**: Theme, Question
    - **Value Objects**: Hint, Answer
  - Storage: 
    - Core entities:
      - **Themes**: id, theme, metadata
      - **Questions**: id, theme_fk, text, answer, hint, difficulty, metadata
    - Data relationships : Questions belong to themes
  - Notes: easily cache popular themes; can be read-replicated/CDN’ed if needed.
3. **Leaderboard Service**: 
  - Responsibilities: compute top-10, success rate, keep historical scores, player statistics.
  - Scaling driver: heavy reads; write via events from Session svc.
  - Interfaces:
    - Queries
      - GET /leaderboard/top10 → Get top 10 scores
      - GET /leaderboard/players/{id} → Get player ranking and history
      - GET /leaderboard/stats → Get game statistics
    - Commands
      - POST /leaderboard/update → Update scores (internal)
  - Storage: 
    - Core entities:
      - **Scores**: session_id, player, points, duration, questions_answered, correct_count, created_at 
      - **Leaderboard**: Aggregated scores and rankings (top10 materialized view/cache)
    - Data relationships : Leaderboard aggregates from GameSessions
  - Notes: can be eventually consistent (seconds). Cache responses (Redis) with short TTL.
4. **User Service**: Player registration and profile management
  - Responsibilities: Identity & Accounts management including email verification, Consent & Compliance (GDPR)
  - Scaling driver: registration bursts (marketing campaigns), auth traffic
  - Interfaces:
    - Queries
      - GET    /users/{id}            → Get user profile (restricted to the user)
    - Commands
      - POST /users/register → Register new player
      - POST /users/verify-email
      - PUT  /users/{id}            → Update profile
    - Admin
      - GET /admin/users?email=… → Get user profile (PII; protected)
      - GET /admin/users → List all users (admin)
      - POST /admin/users/{id}/block|unblock|delete
      - POST /admin/users/{id}/resend-verification
      - POST /admin/users/{id}/export → enqueues GDPR export job
      - POST /admin/users/{id}/erase → soft-delete + downstream purge events
      - DELETE /users/{id}            → Delete account (GDPR)
  - Domain driven design:
    - **Aggregates**: User
  - Storage: 
    - Core entities:
      - **Users**: ID, name, display_name, created_at, updated_at, deleted_at
      - **user_contact**: email unique, email_verified_at 
      - **user_consent**: marketing_email bool, consent_at, email_token (token unique), purpose (verify|login|change_email), expires_at, used_at
5. **Admin Service**: 
  - Responsibilities: Admin authentication, dashboard, audit logs access
  - Interfaces:
    - Commands
      - POST /admin/auth → Admin authentication
    - Admin
      - GET /admin/dashboard → Dashboard data
      - GET /admin/audit → Audit logs
  - Storage: 
    - Core entities:
      - **AuditLogs**: Admin actions and security events. Security events reference users and actions
6. **Gateway Service**: 
  - Responsibilities: API routing, authentication, rate limiting


## System Architecture Diagram

```
┌────────────────────────────────────────────────────────────────────────────┐
│                            Client Layer                                    │
│  ┌──────────────┐  ┌──────────────┐  ┌───────────────┐  ┌─────────────┐    │
│  │   Web App    │  │  Mobile iOS  │  │ Mobile Android│  │   Desktop   │    │
│  │   (React)    │  │(React Native)│  │(React Native) │  │   (Wails)   │    │
│  └──────────────┘  └──────────────┘  └───────────────┘  └─────────────┘    │
└────────────────────────────────────────────────────────────────────────────┘
                                      │
                               HTTPS/WSS
                                      │
┌─────────────────────────────────────────────────────────────────────────────┐
│                          API Gateway Layer                                  │
│  ┌────────────────────────────────────────────────────────────────────────┐ │
│  │  NGINX + API Gateway Service (Go)                                      │ │
│  │  • Authentication & Authorization                                      │ │
│  │  • Rate Limiting & CORS                                                │ │
│  │  • Request Routing & Load Balancing                                    │ │
│  │  • Security Headers & Input Validation                                 │ │
│  └────────────────────────────────────────────────────────────────────────┘ │
└─────────────────────────────────────────────────────────────────────────────┘
                                      │
                                 gRPC/HTTP
                                      │
┌─────────────────────────────────────────────────────────────────────────────┐
│                        Microservices Layer                                  │
│  ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐            │
│  │ Game Session│ │Question Bank│ │    User     │ │ Leaderboard │            │
│  │   Service   │ │   Service   │ │   Service   │ │   Service   │            │
│  └─────────────┘ └─────────────┘ └─────────────┘ └─────────────┘            │
│  ┌─────────────┐                                                            │
│  │   Admin     │                                                            │
│  │   Service   │                                                            │
│  └─────────────┘                                                            │
└─────────────────────────────────────────────────────────────────────────────┘
                                      │
                              Database Connections
                                      │
┌─────────────────────────────────────────────────────────────────────────────┐
│                         Data & External Layer                               │
│  ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐            │
│  │ PostgreSQL  │ │    Redis    │ │   Zitadel   │ │ Observabi-  │            │
│  │   Primary   │ │   Cache &   │ │   OAuth     │ │    lity     │            │
│  │  Database   │ │  Sessions   │ │  Provider   │ │    Stack    │            │
│  └─────────────┘ └─────────────┘ └─────────────┘ └─────────────┘            │
└─────────────────────────────────────────────────────────────────────────────┘
```

### Frontend Technologies
```yaml
Web Application:
  Framework: React 18.2+
  Language: TypeScript 5.0+
  Build Tool: Vite 4.0+
  UI Library: Gluestack UI (React Native Web)
  Styling: NativeWind/Tailwind CSS 3.0+
  State Management: React Context + useReducer
  Testing: Jest + React Testing Library + Playwright

Mobile Applications:
  Framework: React Native 0.81+
  Language: TypeScript 5.9+
  UI Library: Gluestack UI (Native)
  Navigation: Expo 54+
  State Management: React Context + useReducer
  Testing: Jest + React Native Testing Library

Desktop Application:
  Framework: Wails 2.10+
  Template: wails-vite-react-ts-tailwind-template 
```

### Backend Technologies
```yaml
Microservices:
  Language: Go 1.25+
  HTTP Framework: Fiber 3.0+
  gRPC: Protocol Buffers + gRPC-Go
  Database ORM: Ent (Facebook)
  Authentication: JWT + Zitadel Integration
  Testing: Go testing + testcontainers
  
API Gateway:
  Reverse Proxy: NGINX
  Gateway Service: Go + Fiber
  Load Balancing: Round-robin + Health checks
  Rate Limiting: Redis-based sliding window
```

### Data Technologies for production
```yaml
Primary Database:
  Engine: PostgreSQL 15+
  Connection Pooling: pgxpool
  Migrations: Ent migrations
  Backup: pg_dump + Object Storage

Cache Layer:
  Engine: Redis 7+
  Use Cases: Sessions, Rate limiting, Cache
  Clustering: Redis Cluster (Production)
  Persistence: RDB + AOF

Authentication:
  Provider: Zitadel (Self-hosted)
  Protocol: OAuth 2.0 + OpenID Connect
  Tokens: JWT with RS256 signing
  MFA: TOTP + WebAuthn
```

### Data Technologies for development
```yaml
Primary Database:
  Engine: Sqlite
  Migrations: Ent migrations

Cache Layer:
  Engine: Mock object created for the project

Authentication:
  Provider: Mock object created for the project
  Protocol: OAuth 2.0 + OpenID Connect
  Tokens: JWT with RS256 signing
```

### Inter-Service Communication

#### Service Mesh Architecture
```yaml
Communication Patterns:
  Synchronous: gRPC for real-time operations
  Asynchronous: asynchronous gRPC calls (Event-driven via message queues in the future)
  
Service Discovery:
  Registry: Kubernetes DNS
  Health Checks: HTTP /health endpoints
  Load Balancing: Round-robin with health awareness
  
Circuit Breaker:
  Pattern: Hystrix-style circuit breakers
  Fallback: Graceful degradation
  Timeout: Context-based timeouts
```

#### gRPC Service Definitions
```protobuf
// game_service.proto
service GameService {
  rpc StartGame(StartGameRequest) returns (StartGameResponse);
  rpc SubmitAnswer(SubmitAnswerRequest) returns (SubmitAnswerResponse);
  rpc GetSession(GetSessionRequest) returns (GetSessionResponse);
  rpc EndGame(EndGameRequest) returns (EndGameResponse);
}

// question_service.proto
service QuestionService {
  rpc GetRandomQuestion(RandomQuestionRequest) returns (Question);
  rpc ValidateAnswer(ValidateAnswerRequest) returns (ValidationResponse);
  rpc GetQuestionHint(HintRequest) returns (HintResponse);
}

// leaderboard_service.proto
service LeaderboardService {
  rpc UpdateScore(UpdateScoreRequest) returns (UpdateScoreResponse);
  rpc GetTopScores(TopScoresRequest) returns (TopScoresResponse);
  rpc GetPlayerRank(PlayerRankRequest) returns (PlayerRankResponse);
}
```

## Deployment & Infrastructure

### Development Environment
- **Local Development**: SQLite for rapid iteration
- **Docker Compose**: Containerized development environment
- **Testing**: Comprehensive unit, integration, and E2E testing

### Production Environment
- **Container Orchestration**: Kubernetes for production deployment
- **Database**: PostgreSQL with high availability configuration
- **Monitoring**: Prometheus, Grafana, Jaeger for observability
- **CI/CD**: GitHub Actions for automated testing and deployment

### Cross-Platform Deployment
- **Web**: Standard web application deployment
- **Mobile**: iOS App Store and Google Play Store distribution
- **Desktop**: Wails applications for major operating systems

### Infrastructure Technologies
```yaml
Containerization:
  Runtime: Docker 24+
  Orchestration: Kubernetes 1.28+
  Registry: Private Docker Registry
  
Observability:
  Metrics: Prometheus + Node Exporter
  Visualization: Grafana + Custom Dashboards
  Tracing: Jaeger + OpenTelemetry
  Logging: Structured logging + Loki
  
CI/CD:
  Platform: GitHub Actions
  Testing: Automated test suites
  Security: SAST/DAST scanning
  Deployment: GitOps with ArgoCD
```