"""Async database session management with connection pooling."""

from collections.abc import AsyncGenerator

from sqlalchemy.ext.asyncio import (
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)

from backend.app.core.config import settings

# Create async engine with connection pooling settings from research
# See: 01-RESEARCH.md Pattern 1: Async Database Session Management
engine = create_async_engine(
    settings.database_url,
    pool_size=10,
    max_overflow=20,
    pool_timeout=30,
    pool_recycle=1800,  # 30 minutes - refresh connections
    pool_pre_ping=True,  # Validate connections before use
    echo=False,  # Set True for SQL logging in development
)

# Session factory for creating async sessions
async_session_maker = async_sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False,
)


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency for database sessions.

    Yields an async database session and ensures proper cleanup.

    Usage:
        @app.get("/items")
        async def get_items(db: AsyncSession = Depends(get_db)):
            # Use db session here
            pass
    """
    async with async_session_maker() as session:
        yield session