strat-gameplay-webapp/backend/app/main.py

import asyncio
import logging
from contextlib import asynccontextmanager

import socketio
from fastapi import FastAPI, Request
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import JSONResponse
from sqlalchemy.exc import SQLAlchemyError

from app.api.routes import auth, games, health, teams
from app.config import get_settings
from app.core.exceptions import (
    DatabaseError,
    GameEngineError,
    GameNotFoundError,
    InvalidGameStateError,
)
from app.core.state_manager import state_manager
from app.database.session import engine, init_db
from app.middleware.rate_limit import rate_limiter
from app.monitoring.pool_monitor import init_pool_monitor
from app.services import redis_client
from app.utils.logging import setup_logging
from app.websocket.connection_manager import ConnectionManager
from app.websocket.handlers import register_handlers

logger = logging.getLogger(f"{__name__}.main")

# Background task handles
_eviction_task: asyncio.Task | None = None
_session_expiration_task: asyncio.Task | None = None
_rate_limit_cleanup_task: asyncio.Task | None = None
_pool_monitoring_task: asyncio.Task | None = None


async def periodic_eviction():
    """
    Background task to periodically evict idle games from memory.

    Runs on a configurable interval (default 60 minutes) to:
    1. Evict games that have been idle beyond the timeout threshold
    2. Enforce memory limits by evicting oldest games if over limit
    3. Log memory statistics for monitoring

    This prevents unbounded memory growth from abandoned games.
    """
    settings = get_settings()
    interval = settings.game_eviction_interval_minutes * 60

    logger.info(
        f"Starting periodic eviction task (interval: {settings.game_eviction_interval_minutes}m, "
        f"idle timeout: {settings.game_idle_timeout_hours}h, max games: {settings.game_max_in_memory})"
    )

    while True:
        try:
            await asyncio.sleep(interval)

            # Run idle game eviction
            evicted = await state_manager.evict_idle_games()

            # Enforce memory limit
            force_evicted = await state_manager.enforce_memory_limit()

            # Log stats
            stats = state_manager.get_memory_stats()
            logger.info(
                f"Eviction cycle complete: {len(evicted)} idle + {len(force_evicted)} forced. "
                f"Active: {stats['active_games']}/{stats['max_games']}, "
                f"Oldest: {stats['oldest_game_hours']:.1f}h"
            )

        except asyncio.CancelledError:
            logger.info("Eviction task cancelled - shutting down")
            break
        except Exception as e:
            logger.error(f"Eviction task error: {e}", exc_info=True)
            # Continue running despite errors - don't let one failure stop eviction


async def periodic_session_expiration(connection_manager):
    """
    Background task to periodically expire inactive WebSocket sessions.

    Runs every 60 seconds to detect and clean up zombie connections
    that weren't properly closed (network failure, browser crash, etc.).

    This works alongside Socket.io's ping/pong mechanism:
    - Socket.io ping/pong: Detects transport-level disconnections
    - This task: Detects application-level inactivity (no events for extended period)
    """
    settings = get_settings()
    interval = 60  # Check every minute
    timeout = settings.ws_connection_timeout * 5  # 5x timeout = 5 minutes default

    logger.info(
        f"Starting session expiration task (interval: {interval}s, timeout: {timeout}s)"
    )

    while True:
        try:
            await asyncio.sleep(interval)

            # Expire inactive sessions
            expired = await connection_manager.expire_inactive_sessions(timeout)

            # Log stats periodically
            stats = connection_manager.get_stats()
            if stats["total_sessions"] > 0:
                logger.debug(
                    f"Session stats: {stats['total_sessions']} sessions, "
                    f"{stats['unique_users']} users, "
                    f"{stats['active_game_rooms']} active games"
                )

        except asyncio.CancelledError:
            logger.info("Session expiration task cancelled - shutting down")
            break
        except Exception as e:
            logger.error(f"Session expiration task error: {e}", exc_info=True)
            # Continue running despite errors


@asynccontextmanager
async def lifespan(app: FastAPI):
    """Startup and shutdown events"""
    global _eviction_task, _session_expiration_task, _rate_limit_cleanup_task, _pool_monitoring_task
    settings = get_settings()

    # Startup
    logger.info("Starting Paper Dynasty Game Backend")
    setup_logging()

    # Initialize database
    await init_db()
    logger.info("Database initialized")

    # Initialize pool monitor for connection pool observability
    pool_monitor = init_pool_monitor(engine)
    _pool_monitoring_task = asyncio.create_task(
        pool_monitor.start_monitoring(interval_seconds=60)
    )
    logger.info("Pool monitoring initialized")

    # Initialize Redis
    try:
        redis_url = settings.redis_url
        await redis_client.connect(redis_url)
        logger.info(f"Redis initialized: {redis_url}")
    except Exception as e:
        logger.warning(
            f"Redis connection failed: {e}. Position rating caching will be unavailable."
        )

    # Start background eviction task
    logger.info("Starting background eviction task")
    _eviction_task = asyncio.create_task(periodic_eviction())

    # Start session expiration task (connection_manager created in module scope below)
    # Note: This task cleans up zombie WebSocket connections
    logger.info("Starting session expiration task")
    _session_expiration_task = asyncio.create_task(
        periodic_session_expiration(connection_manager)
    )

    # Start rate limiter cleanup task
    # Note: This task cleans up stale rate limit buckets to prevent memory leaks
    logger.info("Starting rate limiter cleanup task")
    _rate_limit_cleanup_task = asyncio.create_task(
        rate_limiter.cleanup_stale_buckets()
    )

    yield

    # Shutdown
    logger.info("Shutting down Paper Dynasty Game Backend")

    # Stop eviction task
    if _eviction_task:
        logger.info("Stopping background eviction task")
        _eviction_task.cancel()
        try:
            await _eviction_task
        except asyncio.CancelledError:
            pass

    # Stop session expiration task
    if _session_expiration_task:
        logger.info("Stopping session expiration task")
        _session_expiration_task.cancel()
        try:
            await _session_expiration_task
        except asyncio.CancelledError:
            pass

    # Stop rate limiter cleanup task
    if _rate_limit_cleanup_task:
        logger.info("Stopping rate limiter cleanup task")
        _rate_limit_cleanup_task.cancel()
        try:
            await _rate_limit_cleanup_task
        except asyncio.CancelledError:
            pass

    # Stop pool monitoring task
    if _pool_monitoring_task:
        logger.info("Stopping pool monitoring task")
        _pool_monitoring_task.cancel()
        try:
            await _pool_monitoring_task
        except asyncio.CancelledError:
            pass

    # Disconnect Redis
    if redis_client.is_connected:
        await redis_client.disconnect()
        logger.info("Redis disconnected")


# Initialize FastAPI app
app = FastAPI(
    title="Paper Dynasty Game Backend",
    description="Real-time baseball game engine for Paper Dynasty leagues",
    version="1.0.0",
    lifespan=lifespan,
)


# Global exception handlers for REST API
@app.exception_handler(GameNotFoundError)
async def game_not_found_handler(request: Request, exc: GameNotFoundError):
    """Handle game not found errors with 404 response."""
    logger.warning(f"Game not found: {exc.game_id}")
    return JSONResponse(
        status_code=404,
        content={"detail": str(exc), "error_code": "GAME_NOT_FOUND"},
    )


@app.exception_handler(InvalidGameStateError)
async def invalid_game_state_handler(request: Request, exc: InvalidGameStateError):
    """Handle invalid game state errors with 400 response."""
    logger.warning(f"Invalid game state: {exc}")
    return JSONResponse(
        status_code=400,
        content={
            "detail": str(exc),
            "error_code": "INVALID_GAME_STATE",
            "current_state": exc.current_state,
            "expected_state": exc.expected_state,
        },
    )


@app.exception_handler(DatabaseError)
async def database_error_handler(request: Request, exc: DatabaseError):
    """Handle database errors with 500 response."""
    logger.error(f"Database error during {exc.operation}: {exc.original_error}")
    return JSONResponse(
        status_code=500,
        content={
            "detail": "Database error occurred",
            "error_code": "DATABASE_ERROR",
            "operation": exc.operation,
        },
    )


@app.exception_handler(GameEngineError)
async def game_engine_error_handler(request: Request, exc: GameEngineError):
    """Handle generic game engine errors with 400 response."""
    logger.warning(f"Game engine error: {exc}")
    return JSONResponse(
        status_code=400,
        content={"detail": str(exc), "error_code": "GAME_ENGINE_ERROR"},
    )


@app.exception_handler(SQLAlchemyError)
async def sqlalchemy_error_handler(request: Request, exc: SQLAlchemyError):
    """Handle SQLAlchemy errors with 500 response."""
    logger.error(f"SQLAlchemy error: {exc}")
    return JSONResponse(
        status_code=500,
        content={
            "detail": "Database error occurred - please retry",
            "error_code": "DATABASE_ERROR",
        },
    )


# CORS middleware
settings = get_settings()
app.add_middleware(
    CORSMiddleware,
    allow_origins=settings.cors_origins,
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

# Initialize Socket.io with ping/pong for connection health
sio = socketio.AsyncServer(
    async_mode="asgi",
    cors_allowed_origins=settings.cors_origins,
    # Ping/pong for detecting dead connections:
    # - Server sends ping every ping_interval seconds
    # - Client must respond with pong within ping_timeout seconds
    # - Total: connection dies after (ping_interval + ping_timeout) of no response
    ping_interval=settings.ws_heartbeat_interval,  # Default: 30s
    ping_timeout=settings.ws_connection_timeout,  # Default: 60s
    logger=True,
    engineio_logger=False,
)

# Create Socket.io ASGI app
socket_app = socketio.ASGIApp(sio, app)

# Initialize connection manager and register handlers
connection_manager = ConnectionManager(sio)
register_handlers(sio, connection_manager)

# Configure game engine with connection manager for real-time event emission
from app.core.game_engine import game_engine
game_engine.set_connection_manager(connection_manager)

# Include API routes
app.include_router(health.router, prefix="/api", tags=["health"])
app.include_router(auth.router, prefix="/api/auth", tags=["auth"])
app.include_router(games.router, prefix="/api/games", tags=["games"])
app.include_router(teams.router, prefix="/api/teams", tags=["teams"])


@app.get("/")
async def root():
    return {"message": "Paper Dynasty Game Backend", "version": "1.0.0"}


@app.get("/api/health/connections", tags=["health"])
async def connections_health():
    """
    WebSocket connection statistics for health monitoring.

    Returns:
    - total_sessions: Number of active WebSocket connections
    - unique_users: Number of unique authenticated users
    - active_game_rooms: Number of games with connected players
    - sessions_per_game: Breakdown of connections per game
    - inactivity_distribution: Sessions grouped by inactivity period
    - status: healthy (<50 sessions), warning (50-100), critical (>100)
    """
    import pendulum

    stats = connection_manager.get_stats()

    # Determine health status based on session count
    # Thresholds can be adjusted based on expected load
    total = stats["total_sessions"]
    if total > 100:
        status = "critical"
    elif total > 50:
        status = "warning"
    else:
        status = "healthy"

    # Include rate limiter stats
    rate_limit_stats = rate_limiter.get_stats()

    return {
        "status": status,
        **stats,
        "rate_limiter": rate_limit_stats,
        "ping_interval_seconds": settings.ws_heartbeat_interval,
        "ping_timeout_seconds": settings.ws_connection_timeout,
        "session_expiration_timeout_seconds": settings.ws_connection_timeout * 5,
        "timestamp": pendulum.now("UTC").to_iso8601_string(),
    }


if __name__ == "__main__":
    import uvicorn

    uvicorn.run(
        "app.main:socket_app", host="0.0.0.0", port=8000, reload=True, log_level="info"
    )