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# Paper Dynasty Real-Time Game Engine - Development Guide

## Project Overview

Web-based real-time multiplayer baseball simulation platform replacing legacy Google Sheets system. Consists of:
- **Shared Backend**: FastAPI (Python 3.11+) with WebSocket support, PostgreSQL persistence
- **Dual Frontends**: Separate Vue 3/Nuxt 3 apps per league (SBA and PD) with shared component library

**Critical Business Driver**: Legacy Google Sheets being deprecated - this is mission-critical replacement.

## Architecture Principles

### Backend Philosophy
- **Hybrid State Model**: In-memory game state for performance + PostgreSQL for persistence/recovery
- **League-Agnostic Core**: Polymorphic player models, config-driven league variations
- **Async-First**: All I/O operations use async/await patterns
- **Type Safety**: Pydantic models for validation, SQLAlchemy for ORM

### Frontend Philosophy
- **Mobile-First**: Primary design target is mobile portrait mode
- **Real-Time Updates**: WebSocket (Socket.io) for all game state changes
- **Shared Components**: Maximize reuse between league frontends
- **Type Safety**: TypeScript with strict mode

## Technology Stack

### Backend
- FastAPI + Socket.io (WebSocket)
- PostgreSQL 14+ with SQLAlchemy 2.0
- Pydantic for data validation
- pytest for testing

### Frontend (Per League)
- Vue 3 Composition API + Nuxt 3
- TypeScript (strict mode)
- Tailwind CSS
- Pinia for state management
- Socket.io-client
- @nuxtjs/auth-next (Discord OAuth)

## Key Technical Patterns

### Polymorphic Player Architecture
Use factory pattern for league-specific player types:
- `BasePlayer` (abstract base)
- `SbaPlayer` (simple model)
- `PdPlayer` (detailed scouting data)
- `Lineup.from_api_data(config, data)` factory method

### WebSocket Event Flow
1. Player action → WebSocket → Backend
2. Validate against in-memory state
3. Process + resolve outcome
4. Update in-memory state
5. Async write to PostgreSQL
6. Broadcast state update to all clients

### Game State Recovery
On reconnect: Load plays from DB → Replay to rebuild state → Send current state

## Project Structure

```
strat-gameplay-webapp/
├── backend/              # FastAPI game engine
│   ├── app/
│   │   ├── core/         # Game engine, dice, state management
│   │   ├── config/       # League configs and result charts
│   │   ├── websocket/    # Socket.io handlers
│   │   ├── models/       # Pydantic + SQLAlchemy models
│   │   └── api/          # REST endpoints
│   └── tests/
├── frontend-sba/         # SBA League Nuxt app
├── frontend-pd/          # PD League Nuxt app
└── shared-components/    # Shared Vue components (optional)
```

## Development Guidelines

### Code Quality
- **Python**: Dataclasses preferred, rotating loggers with `f'{__name__}.<className>'`
- **Error Handling**: "Raise or Return" pattern - no Optional unless required
- **Testing**: Run tests freely without asking permission
- **Imports**: Always verify imports during code review to prevent NameErrors
- **Git Commits**: Prefix with "CLAUDE: "

### Performance Targets
- Action response: < 500ms
- WebSocket delivery: < 200ms
- DB writes: < 100ms (async)
- State recovery: < 2 seconds

### Security Requirements
- Discord OAuth for authentication
- Server-side game logic only (zero client trust)
- Cryptographically secure dice rolls
- All rules enforced server-side

## Phase 1 MVP Scope (Weeks 1-13)

**Core Deliverables**:
1. Authentication (Discord OAuth)
2. Game creation & lobby
3. Complete turn-based gameplay with all strategic decisions
4. Real-time WebSocket updates
5. Game persistence & recovery
6. Spectator mode
7. Mobile-optimized UI
8. AI opponent support

**Explicitly Out of Scope for MVP**:
- Roster management
- Marketplace
- Tournaments
- Advanced analytics

## Critical References

- **Full PRD**: `/mnt/NV2/Development/strat-gameplay-webapp/prd-web-scorecard-1.1.md`
- **Player Model Architecture**: PRD lines 378-551
- **Database Schema**: PRD lines 553-628
- **WebSocket Events**: PRD lines 630-669
- **League Config System**: PRD lines 780-846

## League Differences

### SBA League
- Minimal player data (id, name, image)
- Simpler rules configuration

### PD League
- Detailed scouting data on players
- Complex probability calculations
- Additional analytics requirements

## Success Metrics

- 90% player migration within 1 month
- 99.5% uptime
- < 500ms average action latency
- 60%+ mobile usage
- Zero data corruption

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**Note**: Subdirectories will have their own CLAUDE.md files with implementation-specific details to minimize context usage.