# 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.

## Technology Stack

- **Framework**: FastAPI (Python 3.13)
- **WebSocket**: Socket.io (python-socketio)
- **Database**: PostgreSQL 14+ with SQLAlchemy 2.0 (async)
- **ORM**: SQLAlchemy with asyncpg driver
- **Validation**: Pydantic v2
- **DateTime**: Pendulum 3.0 (replaces Python's datetime module)
- **Testing**: pytest with pytest-asyncio
- **Code Quality**: black, flake8, mypy

## Project Structure

```
backend/
├── app/
│   ├── main.py                 # FastAPI app + Socket.io initialization
│   ├── config.py               # Settings with pydantic-settings
│   │
│   ├── core/                   # Game logic (Phase 2+)
│   │   ├── game_engine.py      # Main game simulation
│   │   ├── state_manager.py    # In-memory state
│   │   ├── play_resolver.py    # Play outcome resolution
│   │   ├── dice.py             # Secure random rolls
│   │   └── validators.py       # Rule validation
│   │
│   ├── config/                 # League configurations (Phase 2+)
│   │   ├── base_config.py      # Shared configuration
│   │   ├── league_configs.py   # SBA/PD specific
│   │   └── result_charts.py    # d20 outcome tables
│   │
│   ├── models/                 # Data models
│   │   ├── db_models.py        # SQLAlchemy ORM models
│   │   ├── game_models.py      # Pydantic game state models (Phase 2+)
│   │   └── player_models.py    # Polymorphic player models (Phase 2+)
│   │
│   ├── websocket/              # WebSocket handling
│   │   ├── connection_manager.py  # Connection lifecycle
│   │   ├── handlers.py            # Event handlers
│   │   └── events.py              # Event definitions (Phase 2+)
│   │
│   ├── api/                    # REST API
│   │   ├── routes/
│   │   │   ├── health.py       # Health check endpoints
│   │   │   ├── auth.py         # Discord OAuth (Phase 1)
│   │   │   └── games.py        # Game CRUD (Phase 2+)
│   │   └── dependencies.py     # FastAPI dependencies
│   │
│   ├── database/               # Database layer
│   │   ├── session.py          # Async session management
│   │   └── operations.py       # DB operations (Phase 2+)
│   │
│   ├── data/                   # External data (Phase 2+)
│   │   ├── api_client.py       # League REST API client
│   │   └── cache.py            # Caching layer
│   │
│   └── utils/                  # Utilities
│       ├── logging.py          # Logging setup
│       └── auth.py             # JWT utilities (Phase 1)
│
├── tests/
│   ├── unit/                   # Unit tests
│   ├── integration/            # Integration tests
│   └── e2e/                    # End-to-end tests
│
├── logs/                       # Application logs (gitignored)
├── venv/                       # Virtual environment (gitignored)
├── .env                        # Environment variables (gitignored)
├── .env.example                # Environment template
├── requirements.txt            # Production dependencies
├── requirements-dev.txt        # Dev dependencies
├── Dockerfile                  # Container definition
├── docker-compose.yml          # Redis for local dev
└── pytest.ini                  # Pytest configuration
```

## Key Architectural Patterns

### 1. Hybrid State Management
- **In-Memory**: Active game states for fast access (<500ms response)
- **PostgreSQL**: Persistent storage for recovery and history
- **Pattern**: Write-through cache (update memory + async DB write)

### 2. Polymorphic Player Models
```python
# Base class with abstract methods
class BasePlayer(BaseModel, ABC):
    @abstractmethod
    def get_image_url(self) -> str: ...

# League-specific implementations
class SbaPlayer(BasePlayer): ...
class PdPlayer(BasePlayer): ...

# Factory pattern for instantiation
Lineup.from_api_data(config, data)
```

### 3. League-Agnostic Core
- Game engine works for any league
- League-specific logic in config classes
- Result charts loaded per league

### 4. Async-First
- All database operations use `async/await`
- Database writes don't block game logic
- Connection pooling for efficiency

## Development Workflow

### Daily Development
```bash
# Activate virtual environment
source venv/bin/activate

# Start Redis (in separate terminal or use -d for detached)
docker compose up -d

# Run backend with hot-reload
python -m app.main

# Backend available at http://localhost:8000
# API docs at http://localhost:8000/docs
```

### Testing
```bash
# Run all tests
pytest tests/ -v

# Run with coverage
pytest tests/ --cov=app --cov-report=html

# Run specific test file
pytest tests/unit/test_game_engine.py -v

# Type checking
mypy app/

# Code formatting
black app/ tests/

# Linting
flake8 app/ tests/
```

## Coding Standards

### Python Style
- **Formatting**: Black with default settings
- **Line Length**: 88 characters (black default)
- **Imports**: Group stdlib, third-party, local (isort compatible)
- **Type Hints**: Required for all public functions
- **Docstrings**: Google style for classes and public methods

### Logging Pattern
```python
import logging

logger = logging.getLogger(f'{__name__}.ClassName')

# Usage
logger.info(f"User {user_id} connected")
logger.error(f"Failed to process action: {error}", exc_info=True)
```

### DateTime Handling
**ALWAYS use Pendulum, NEVER use Python's datetime module:**
```python
import pendulum

# Get current UTC time
now = pendulum.now('UTC')

# Format for display
formatted = now.format('YYYY-MM-DD HH:mm:ss')
formatted_iso = now.to_iso8601_string()

# Parse dates
parsed = pendulum.parse('2025-10-21')

# Timezones
eastern = pendulum.now('America/New_York')
utc = eastern.in_timezone('UTC')

# Database defaults (in models)
created_at = Column(DateTime, default=lambda: pendulum.now('UTC'))
```

### Error Handling
- **Raise or Return**: Never return `Optional` unless specifically required
- **Custom Exceptions**: Use for domain-specific errors
- **Logging**: Always log exceptions with context

### Dataclasses
```python
from dataclasses import dataclass

@dataclass
class GameState:
    game_id: str
    inning: int
    outs: int
    # ... fields
```

## Database Models

Our database schema is designed based on the proven Discord game implementation, with enhancements for web real-time gameplay.

### Core Tables

#### **Game** (`games`)
Primary game container with state tracking.

**Key Fields:**
- `id` (UUID): Primary key, prevents ID collisions across distributed systems
- `league_id` (String): 'sba' or 'pd', determines league-specific behavior
- `status` (String): 'pending', 'active', 'completed'
- `game_mode` (String): 'ranked', 'friendly', 'practice'
- `visibility` (String): 'public', 'private'
- `current_inning`, `current_half`: Current game state
- `home_score`, `away_score`: Running scores

**AI Support:**
- `home_team_is_ai` (Boolean): Home team controlled by AI
- `away_team_is_ai` (Boolean): Away team controlled by AI
- `ai_difficulty` (String): 'balanced', 'yolo', 'safe'

**Relationships:**
- `plays`: All plays in the game (cascade delete)
- `lineups`: All lineup entries (cascade delete)
- `cardset_links`: PD only - approved cardsets (cascade delete)
- `roster_links`: Roster tracking - cards (PD) or players (SBA) (cascade delete)
- `session`: Real-time WebSocket session (cascade delete)

---

#### **Play** (`plays`)
Records every at-bat with full statistics and game state.

**Game State Snapshot:**
- `play_number`: Sequential play counter
- `inning`, `half`: Inning state
- `outs_before`: Outs at start of play
- `batting_order`: Current spot in order
- `away_score`, `home_score`: Score at play start

**Player References (FKs to Lineup):**
- `batter_id`, `pitcher_id`, `catcher_id`: Required players
- `defender_id`, `runner_id`: Optional for specific plays
- `on_first_id`, `on_second_id`, `on_third_id`: Base runners

**Runner Outcomes:**
- `on_first_final`, `on_second_final`, `on_third_final`: Final base (None = out, 1-4 = base)
- `batter_final`: Where batter ended up
- `on_base_code` (Integer): Bit field for efficient queries (1=1st, 2=2nd, 4=3rd, 7=loaded)

**Strategic Decisions:**
- `defensive_choices` (JSON): Alignment, holds, shifts
- `offensive_choices` (JSON): Steal attempts, bunts, hit-and-run

**Play Result:**
- `dice_roll` (String): Dice notation (e.g., "14+6")
- `hit_type` (String): GB, FB, LD, etc.
- `result_description` (Text): Human-readable result
- `outs_recorded`, `runs_scored`: Play outcome
- `check_pos` (String): Defensive position for X-check

**Batting Statistics (25+ fields):**
- `pa`, `ab`, `hit`, `double`, `triple`, `homerun`
- `bb`, `so`, `hbp`, `rbi`, `sac`, `ibb`, `gidp`
- `sb`, `cs`: Base stealing
- `wild_pitch`, `passed_ball`, `pick_off`, `balk`
- `bphr`, `bpfo`, `bp1b`, `bplo`: Ballpark power events
- `run`, `e_run`: Earned/unearned runs

**Advanced Analytics:**
- `wpa` (Float): Win Probability Added
- `re24` (Float): Run Expectancy 24 base-out states

**Game Situation Flags:**
- `is_tied`, `is_go_ahead`, `is_new_inning`: Context flags
- `in_pow`: Pitcher over workload
- `complete`, `locked`: Workflow state

**Helper Properties:**
```python
@property
def ai_is_batting(self) -> bool:
    """True if batting team is AI-controlled"""
    return (self.half == 'top' and self.game.away_team_is_ai) or \
           (self.half == 'bot' and self.game.home_team_is_ai)

@property
def ai_is_fielding(self) -> bool:
    """True if fielding team is AI-controlled"""
    return not self.ai_is_batting
```

---

#### **Lineup** (`lineups`)
Tracks player assignments and substitutions.

**Key Fields:**
- `game_id`, `team_id`, `card_id`: Links to game/team/card
- `position` (String): P, C, 1B, 2B, 3B, SS, LF, CF, RF, DH
- `batting_order` (Integer): 1-9

**Substitution Tracking:**
- `is_starter` (Boolean): Original lineup vs substitute
- `is_active` (Boolean): Currently in game
- `entered_inning` (Integer): When player entered
- `replacing_id` (Integer): Lineup ID of replaced player
- `after_play` (Integer): Exact play number of substitution

**Pitcher Management:**
- `is_fatigued` (Boolean): Triggers bullpen decisions

---

#### **GameCardsetLink** (`game_cardset_links`)
PD league only - defines legal cardsets for a game.

**Key Fields:**
- `game_id`, `cardset_id`: Composite primary key
- `priority` (Integer): 1 = primary, 2+ = backup

**Usage:**
- SBA games: Empty (no cardset restrictions)
- PD games: Required (validates card eligibility)

---

#### **RosterLink** (`roster_links`)
Tracks eligible cards (PD) or players (SBA) for a game.

**Polymorphic Design**: Single table supporting both leagues with application-layer type safety.

**Key Fields:**
- `id` (Integer): Surrogate primary key (auto-increment)
- `game_id` (UUID): Foreign key to games table
- `card_id` (Integer, nullable): PD league - card identifier
- `player_id` (Integer, nullable): SBA league - player identifier
- `team_id` (Integer): Which team owns this entity in this game

**Constraints:**
- `roster_link_one_id_required`: CHECK constraint ensures exactly one of `card_id` or `player_id` is populated (XOR logic)
- `uq_game_card`: UNIQUE constraint on (game_id, card_id) for PD
- `uq_game_player`: UNIQUE constraint on (game_id, player_id) for SBA

**Usage Pattern:**
```python
# PD league - add card to roster
roster_data = await db_ops.add_pd_roster_card(
    game_id=game_id,
    card_id=123,
    team_id=1
)

# SBA league - add player to roster
roster_data = await db_ops.add_sba_roster_player(
    game_id=game_id,
    player_id=456,
    team_id=2
)

# Get roster (league-specific)
pd_roster = await db_ops.get_pd_roster(game_id, team_id=1)
sba_roster = await db_ops.get_sba_roster(game_id, team_id=2)
```

**Design Rationale:**
- Single table avoids complex joins and simplifies queries
- Nullable columns with CHECK constraint ensures data integrity at database level
- Pydantic models (`PdRosterLinkData`, `SbaRosterLinkData`) provide type safety at application layer
- Surrogate key allows nullable columns (can't use nullable columns in composite PK)

---

#### **GameSession** (`game_sessions`)
Real-time WebSocket state tracking.

**Key Fields:**
- `game_id` (UUID): Primary key, one-to-one with Game
- `connected_users` (JSON): Active WebSocket connections
- `last_action_at` (DateTime): Last activity timestamp
- `state_snapshot` (JSON): In-memory game state cache

---

### Database Patterns

### Async Session Usage
```python
from app.database.session import get_session

async def some_function():
    async with get_session() as session:
        result = await session.execute(query)
        # session.commit() happens automatically
```

### Model Definitions
```python
from app.database.session import Base
from sqlalchemy import Column, String, Integer

class Game(Base):
    __tablename__ = "games"

    id = Column(UUID(as_uuid=True), primary_key=True)
    # ... columns
```

### Relationship Patterns

**Using Lazy Loading:**
```python
# In Play model - common players loaded automatically
batter = relationship("Lineup", foreign_keys=[batter_id], lazy="joined")
pitcher = relationship("Lineup", foreign_keys=[pitcher_id], lazy="joined")

# Rare players loaded on demand
defender = relationship("Lineup", foreign_keys=[defender_id])  # lazy="select" (default)
```

**Querying with Relationships:**
```python
from sqlalchemy.orm import joinedload

# Efficient loading for broadcasting
play = await session.execute(
    select(Play)
    .options(
        joinedload(Play.batter),
        joinedload(Play.pitcher),
        joinedload(Play.on_first),
        joinedload(Play.on_second),
        joinedload(Play.on_third)
    )
    .where(Play.id == play_id)
)
```

### Common Query Patterns

**Find plays with bases loaded:**
```python
# Using on_base_code bit field
bases_loaded_plays = await session.execute(
    select(Play).where(Play.on_base_code == 7)  # 1+2+4 = 7
)
```

**Get active pitcher for team:**
```python
pitcher = await session.execute(
    select(Lineup)
    .where(
        Lineup.game_id == game_id,
        Lineup.team_id == team_id,
        Lineup.position == 'P',
        Lineup.is_active == True
    )
)
```

**Calculate box score stats:**
```python
# Player batting stats for game
stats = await session.execute(
    select(
        func.sum(Play.ab).label('ab'),
        func.sum(Play.hit).label('hits'),
        func.sum(Play.homerun).label('hr'),
        func.sum(Play.rbi).label('rbi')
    )
    .where(
        Play.game_id == game_id,
        Play.batter_id == lineup_id
    )
)
```

## WebSocket Patterns

### Event Handler Registration
```python
@sio.event
async def some_event(sid, data):
    """Handle some_event from client"""
    try:
        # Validate data
        # Process action
        # Emit response
        await sio.emit('response_event', result, room=sid)
    except Exception as e:
        logger.error(f"Error handling event: {e}")
        await sio.emit('error', {'message': str(e)}, room=sid)
```

### Broadcasting
```python
# To specific game room
await connection_manager.broadcast_to_game(
    game_id,
    'game_state_update',
    state_data
)

# To specific user
await connection_manager.emit_to_user(
    sid,
    'decision_required',
    decision_data
)
```

## Environment Variables

Required in `.env`:
```bash
# Database
DATABASE_URL=postgresql+asyncpg://user:pass@host:5432/dbname

# Application
SECRET_KEY=your-secret-key-at-least-32-chars

# Discord OAuth
DISCORD_CLIENT_ID=your-client-id
DISCORD_CLIENT_SECRET=your-client-secret

# League APIs
SBA_API_URL=https://sba-api.example.com
SBA_API_KEY=your-api-key
PD_API_URL=https://pd-api.example.com
PD_API_KEY=your-api-key
```

## Performance Targets

- **Action Response**: < 500ms from user action to state update
- **WebSocket Delivery**: < 200ms
- **Database Write**: < 100ms (async, non-blocking)
- **State Recovery**: < 2 seconds
- **Concurrent Games**: Support 10+ simultaneous games
- **Memory**: < 1GB with 10 active games

## Security Considerations

- **Authentication**: All WebSocket connections require valid JWT
- **Authorization**: Verify team ownership before allowing actions
- **Input Validation**: Pydantic models validate all inputs
- **SQL Injection**: Prevented by SQLAlchemy ORM
- **Dice Rolls**: Cryptographically secure random generation
- **Server-Side Logic**: All game rules enforced server-side

## Common Tasks

### Adding a New API Endpoint
1. Create route in `app/api/routes/`
2. Define Pydantic request/response models
3. Add dependency injection if needed
4. Register router in `app/main.py`

### Adding a New WebSocket Event
1. Define event handler in `app/websocket/handlers.py`
2. Register with `@sio.event` decorator
3. Validate data with Pydantic
4. Add corresponding client handling in frontend

### Adding a New Database Model
1. Define SQLAlchemy model in `app/models/db_models.py`
2. Create Alembic migration: `alembic revision --autogenerate -m "description"`
3. Apply migration: `alembic upgrade head`

## Troubleshooting

### Import Errors
- Ensure virtual environment is activated
- Check `PYTHONPATH` if using custom structure
- Verify all `__init__.py` files exist

### Database Connection Issues
- Verify `DATABASE_URL` in `.env` is correct
- Test connection: `psql $DATABASE_URL`
- Check firewall/network access
- Verify database exists

### WebSocket Not Connecting
- Check CORS settings in `config.py`
- Verify token is being sent from client
- Check logs for connection errors
- Ensure Socket.io versions match (client/server)

## Environment-Specific Configuration

### Database Connection
- **Dev Server**: PostgreSQL at `10.10.0.42:5432`
- **Database Name**: `paperdynasty_dev`
- **User**: `paperdynasty`
- **Connection String Format**: `postgresql+asyncpg://paperdynasty:PASSWORD@10.10.0.42:5432/paperdynasty_dev`

### Docker Compose Commands
This system uses **Docker Compose V2** (not legacy docker-compose):
```bash
# Correct (with space)
docker compose up -d
docker compose down
docker compose logs

# Incorrect (will not work)
docker-compose up -d  # Old command not available
```

### Python Environment
- **Version**: Python 3.13.3 (not 3.11 as originally planned)
- **Virtual Environment**: Located at `backend/venv/`
- **Activation**: `source venv/bin/activate` (from backend directory)

### Critical Dependencies
- **greenlet**: Required for SQLAlchemy async support (must be explicitly installed)
- **Pendulum**: Used for ALL datetime operations (replaces Python's datetime module)
  ```python
  import pendulum

  # Always use Pendulum
  now = pendulum.now('UTC')

  # Never use
  from datetime import datetime  # ❌ Don't import this
  ```

### Environment Variable Format

**IMPORTANT**: Pydantic Settings requires specific formats for complex types:

```bash
# Lists must be JSON arrays
CORS_ORIGINS=["http://localhost:3000", "http://localhost:3001"]  # ✅ Correct

# NOT comma-separated strings
CORS_ORIGINS=http://localhost:3000,http://localhost:3001  # ❌ Will fail
```

### SQLAlchemy Reserved Names

The following column names are **reserved** in SQLAlchemy and will cause errors:

```python
# ❌ NEVER use these as column names
metadata = Column(JSON)  # RESERVED - will fail

# ✅ Use descriptive alternatives
game_metadata = Column(JSON)
play_metadata = Column(JSON)
lineup_metadata = Column(JSON)
```

**Other reserved names to avoid**: `metadata`, `registry`, `__tablename__`, `__mapper__`, `__table__`

### Package Version Notes

Due to Python 3.13 compatibility, we use newer versions than originally planned:

```txt
# Updated versions (from requirements.txt)
fastapi==0.115.6          # (was 0.104.1)
uvicorn==0.34.0           # (was 0.24.0)
pydantic==2.10.6          # (was 2.5.0)
sqlalchemy==2.0.36        # (was 2.0.23)
asyncpg==0.30.0           # (was 0.29.0)
pendulum==3.0.0           # (new addition)
```

### Server Startup

```bash
# From backend directory with venv activated
python -m app.main

# Server runs at:
# - Main API: http://localhost:8000
# - Swagger UI: http://localhost:8000/docs
# - ReDoc: http://localhost:8000/redoc

# With hot-reload enabled by default
```

### Logs Directory
- Auto-created at `backend/logs/`
- Daily rotating logs: `app_YYYYMMDD.log`
- 10MB max size, 5 backup files
- Gitignored

## Week 4 Implementation (Phase 2 - State Management)

**Completed**: 2025-10-22
**Status**: ✅ **COMPLETE** - All deliverables achieved

### Components Implemented

#### 1. Pydantic Game State Models (`app/models/game_models.py`)

**Purpose**: Type-safe models for in-memory game state representation

**Key Models**:
- `GameState`: Core game state (inning, score, runners, decisions)
- `RunnerState`: Base runner tracking
- `LineupPlayerState` / `TeamLineupState`: Lineup management
- `DefensiveDecision` / `OffensiveDecision`: Strategic decisions

**Features**:
- Full Pydantic v2 validation with field validators
- 20+ helper methods on GameState
- Optimized for fast serialization (WebSocket broadcasts)
- Game over logic, runner advancement, scoring

**Usage Example**:
```python
from app.models.game_models import GameState, RunnerState

# Create game state
state = GameState(
    game_id=uuid4(),
    league_id="sba",
    home_team_id=1,
    away_team_id=2
)

# Add runner
state.add_runner(lineup_id=1, card_id=101, base=1)

# Advance runner and score
state.advance_runner(from_base=1, to_base=4)  # Scores run
```

#### 2. State Manager (`app/core/state_manager.py`)

**Purpose**: In-memory state management with O(1) lookups

**Key Features**:
- Dictionary-based storage: `_states: Dict[UUID, GameState]`
- Lineup caching per game
- Last access tracking with Pendulum timestamps
- Idle game eviction (configurable timeout)
- State recovery from database
- Statistics tracking

**Usage Example**:
```python
from app.core.state_manager import state_manager

# Create game
state = await state_manager.create_game(
    game_id=game_id,
    league_id="sba",
    home_team_id=1,
    away_team_id=2
)

# Get state (fast O(1) lookup)
state = state_manager.get_state(game_id)

# Update state
state.inning = 5
state_manager.update_state(game_id, state)

# Recover from database
recovered = await state_manager.recover_game(game_id)
```

**Performance**:
- State access: O(1) via dictionary lookup
- Memory per game: ~1KB (just state, no player data yet)
- Target response time: <500ms ✅

#### 3. Database Operations (`app/database/operations.py`)

**Purpose**: Async PostgreSQL persistence layer

**Key Methods**:
- `create_game()`: Create game in database
- `update_game_state()`: Update inning, score, status
- `create_lineup_entry()` / `get_active_lineup()`: Lineup persistence
- `save_play()` / `get_plays()`: Play recording
- `load_game_state()`: Complete state loading for recovery
- `create_game_session()` / `update_session_snapshot()`: WebSocket state

**Usage Example**:
```python
from app.database.operations import DatabaseOperations

db_ops = DatabaseOperations()

# Create game
await db_ops.create_game(
    game_id=game_id,
    league_id="sba",
    home_team_id=1,
    away_team_id=2,
    game_mode="friendly",
    visibility="public"
)

# Update state (async, non-blocking)
await db_ops.update_game_state(
    game_id=game_id,
    inning=5,
    half="bottom",
    home_score=3,
    away_score=2
)

# Load for recovery
game_data = await db_ops.load_game_state(game_id)
```

**Pattern**: All operations use async/await with proper error handling

### Testing

**Unit Tests** (86 tests, 100% passing):
- `tests/unit/models/test_game_models.py` (60 tests)
- `tests/unit/core/test_state_manager.py` (26 tests)

**Integration Tests** (29 tests written):
- `tests/integration/database/test_operations.py` (21 tests)
- `tests/integration/test_state_persistence.py` (8 tests)

**Run Tests**:
```bash
# All unit tests
pytest tests/unit/ -v

# Integration tests (requires database)
pytest tests/integration/ -v -m integration

# Specific file
pytest tests/unit/models/test_game_models.py -v
```

### Patterns Established

#### 1. Pydantic Field Validation
```python
@field_validator('position')
@classmethod
def validate_position(cls, v: str) -> str:
    valid_positions = ['P', 'C', '1B', '2B', '3B', 'SS', 'LF', 'CF', 'RF', 'DH']
    if v not in valid_positions:
        raise ValueError(f"Position must be one of {valid_positions}")
    return v
```

#### 2. Async Database Session Management
```python
async with AsyncSessionLocal() as session:
    try:
        # database operations
        await session.commit()
    except Exception as e:
        await session.rollback()
        logger.error(f"Error: {e}")
        raise
```

#### 3. State Recovery Pattern
```python
# 1. Load from database
game_data = await db_ops.load_game_state(game_id)

# 2. Rebuild in-memory state
state = await state_manager._rebuild_state_from_data(game_data)

# 3. Cache in memory
state_manager._states[game_id] = state
```

#### 4. Helper Methods on Models
```python
# GameState helper methods
def get_batting_team_id(self) -> int:
    return self.away_team_id if self.half == "top" else self.home_team_id

def is_runner_on_first(self) -> bool:
    return any(r.on_base == 1 for r in self.runners)

def advance_runner(self, from_base: int, to_base: int) -> None:
    # Auto-score when to_base == 4
    if to_base == 4:
        if self.half == "top":
            self.away_score += 1
        else:
            self.home_score += 1
```

### Configuration

**pytest.ini** (created):
```ini
[pytest]
asyncio_mode = auto
asyncio_default_fixture_loop_scope = function
```

**Fixed Warnings**:
- ✅ Pydantic v2 config deprecation (migrated to `model_config = ConfigDict()`)
- ✅ pytest-asyncio loop scope configuration

### Key Files

```
app/models/game_models.py      (492 lines) - Pydantic state models
app/core/state_manager.py      (296 lines) - In-memory state management
app/database/operations.py     (362 lines) - Async database operations
tests/unit/models/test_game_models.py      (788 lines, 60 tests)
tests/unit/core/test_state_manager.py      (447 lines, 26 tests)
tests/integration/database/test_operations.py      (438 lines, 21 tests)
tests/integration/test_state_persistence.py        (290 lines, 8 tests)
pytest.ini                     (23 lines)  - Test configuration
```

### Next Phase (Week 5)

Week 5 will build game logic on top of this state management foundation:
1. Dice system (cryptographic d20 rolls)
2. Play resolver (result charts and outcome determination)
3. Game engine (orchestrate complete at-bat flow)
4. Rule validators (enforce baseball rules)
5. Enhanced state recovery (replay plays to rebuild complete state)

---

## References

- **Implementation Guide**: `../.claude/implementation/01-infrastructure.md`
- **Backend Architecture**: `../.claude/implementation/backend-architecture.md`
- **Week 4 Plan**: `../.claude/implementation/02-week4-state-management.md`
- **Week 5 Plan**: `../.claude/implementation/02-week5-game-logic.md`
- **Player Data Catalog**: `../.claude/implementation/player-data-catalog.md`
- **WebSocket Protocol**: `../.claude/implementation/websocket-protocol.md`
- **Database Design**: `../.claude/implementation/database-design.md`
- **Full PRD**: `../prd-web-scorecard-1.1.md`

---

**Current Phase**: Phase 2 - Game Engine Core (Week 4 ✅ Complete)
**Next Phase**: Phase 2 - Game Logic (Week 5)

**Phase 1 Completed**: 2025-10-21
**Week 4 Completed**: 2025-10-22
**Python Version**: 3.13.3
**Database Server**: 10.10.0.42:5432

## Database Model Updates (2025-10-21)

Enhanced all database models based on proven Discord game implementation:

### Changes from Initial Design:
- ✅ Added `GameCardsetLink` and `RosterLink` tables for PD league cardset management
- ✅ Enhanced `Game` model with AI opponent support (`home_team_is_ai`, `away_team_is_ai`, `ai_difficulty`)
- ✅ Added 25+ statistic fields to `Play` model (pa, ab, hit, hr, rbi, sb, wpa, re24, etc.)
- ✅ Added player reference FKs to `Play` (batter, pitcher, catcher, defender, runner)
- ✅ Added base runner tracking with `on_base_code` bit field for efficient queries
- ✅ Added game situation flags to `Play` (is_tied, is_go_ahead, is_new_inning, in_pow)
- ✅ Added play workflow flags (complete, locked)
- ✅ Enhanced `Lineup` with substitution tracking (replacing_id, after_play, is_fatigued)
- ✅ Changed strategic decisions to JSON (defensive_choices, offensive_choices)
- ✅ Added helper properties for AI decision-making (ai_is_batting, ai_is_fielding)

### Design Decisions:
- **UUID vs BigInteger**: Kept UUIDs for Game primary key (better for distributed systems)
- **AI Tracking**: Per-team booleans instead of single `ai_team` field (supports AI vs AI simulations)
- **Runner Tracking**: Removed JSON fields, using FKs + `on_base_code` for type safety
- **Cardsets**: Optional relationships - empty for SBA, required for PD
- **Relationships**: Using SQLAlchemy relationships with strategic lazy loading