strat-gameplay-webapp/backend/CLAUDE.md

Backend - Paper Dynasty Game Engine

Overview

FastAPI-based real-time game backend handling WebSocket communication, game state management, and database persistence for both SBA and PD leagues.

Tech Stack: FastAPI (Python 3.13), Socket.io, PostgreSQL 14+, SQLAlchemy 2.0, Pydantic v2, pytest

Project Structure

backend/
├── app/
│   ├── main.py           # FastAPI + Socket.io init
│   ├── config.py         # pydantic-settings
│   ├── core/             # Game engine - see core/CLAUDE.md
│   ├── config/           # League configs - see config/CLAUDE.md
│   ├── models/           # Pydantic + SQLAlchemy - see models/CLAUDE.md
│   ├── websocket/        # Socket.io handlers - see websocket/CLAUDE.md
│   ├── api/              # REST endpoints - see api/CLAUDE.md
│   ├── database/         # Async persistence - see database/CLAUDE.md
│   ├── services/         # Business logic (LineupService, PD API client)
│   └── utils/            # Logging, auth - see utils/CLAUDE.md
├── tests/                # See tests/CLAUDE.md
├── terminal_client/      # Interactive testing - see terminal_client/CLAUDE.md
└── logs/                 # Daily rotating logs (gitignored)

Development

Quick Start

cd backend
uv sync                    # Install dependencies
uv run alembic upgrade head # Apply database migrations
uv run python -m app.main  # Start server at localhost:8000

Testing

uv run pytest tests/unit/ -v           # All unit tests (836 passing)
uv run python -m terminal_client       # Interactive REPL

Code Quality

uv run mypy app/           # Type checking
uv run ruff check app/     # Linting
uv run ruff format app/    # Formatting

Key Patterns

Hybrid State Management

• In-memory: Active game states for <500ms response
• PostgreSQL: Persistent storage for recovery
• Pattern: Write-through cache (update memory + async DB write)

League-Agnostic Core

• Game engine works for any league
• Config-driven behavior (SbaConfig, PdConfig)
• Polymorphic player models (BasePlayer → SbaPlayer, PdPlayer)

DateTime

Always use Pendulum (never Python's datetime):

import pendulum
now = pendulum.now('UTC')

Environment

Database

• Server: PostgreSQL at 10.10.0.42:5432
• Database: paperdynasty_dev
• Connection: postgresql+asyncpg://...

Required .env Variables

DATABASE_URL=postgresql+asyncpg://...
SECRET_KEY=your-secret-key
DISCORD_CLIENT_ID=...
DISCORD_CLIENT_SECRET=...

Python Environment

• Version: Python 3.13.3
• Package Manager: UV (fast, reliable)
• Virtual Environment: backend/.venv/

Testing Policy

REQUIRED: 100% unit tests passing before any commit

uv run pytest tests/unit/ -q  # Must show all passing

Coding Standards

• Formatting: Ruff (88 chars, black-compatible)
• Linting: Ruff (replaces flake8, includes isort, pyupgrade)
• Type Hints: Required for public functions
• Logging: logger = logging.getLogger(f'{__name__}.ClassName')
• Error Handling: "Raise or Return" - no silent failures

Performance Targets

Metric	Target
Action response	< 500ms
WebSocket delivery	< 200ms
DB writes	< 100ms (async)
State recovery	< 2 seconds

References

• WebSocket Protocol Spec: ../.claude/WEBSOCKET_PROTOCOL_SPEC.md - Complete event catalog and workflow
• Type Checking Guide: .claude/type-checking-guide.md
• Code Review: .claude/CODE_REVIEW_GAME_ENGINE.md
• Implementation Plans: ../.claude/implementation/
• Full PRD: ../prd-web-scorecard-1.1.md

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Tests: 836 passing | Phase: 3E-Final Complete | Updated: 2025-01-27