# app/database.py
from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
from sqlalchemy.orm import sessionmaker, declarative_base
from app.config import settings
import logging

logger = logging.getLogger(__name__)

# Ensure DATABASE_URL is set before proceeding
if not settings.DATABASE_URL:
    raise ValueError("DATABASE_URL is not configured in settings.")

# Create the SQLAlchemy async engine
# pool_recycle=3600 helps prevent stale connections on some DBs
engine = create_async_engine(
    settings.DATABASE_URL,
    echo=True,  # Log SQL queries (useful for debugging)
    future=True, # Use SQLAlchemy 2.0 style features
    pool_recycle=3600 # Optional: recycle connections after 1 hour
)

# Create a configured "Session" class
# expire_on_commit=False prevents attributes from expiring after commit
AsyncSessionLocal = sessionmaker(
    bind=engine,
    class_=AsyncSession,
    expire_on_commit=False,
    autoflush=False,
    autocommit=False,
)

# Base class for our ORM models
Base = declarative_base()

# Dependency to get DB session in path operations
async def get_async_session() -> AsyncSession: # type: ignore
    """
    Dependency function that yields an AsyncSession.
    Ensures the session is closed after the request.
    """
    async with AsyncSessionLocal() as session:
        yield session
    # The 'async with' block handles session.close() automatically.
    # Commit/rollback should be handled by the functions using the session.

# Alias for backward compatibility
get_db = get_async_session

async def get_transactional_session() -> AsyncSession: # type: ignore
    """
    Dependency function that yields an AsyncSession wrapped in a transaction.
    Commits on successful completion of the request handler, rolls back on exceptions.
    """
    async with AsyncSessionLocal() as session:
        async with session.begin(): # Start a transaction
            try:
                logger.debug(f"Transaction started for session {id(session)}")
                yield session
                # If no exceptions were raised by the endpoint, the 'session.begin()'
                # context manager will automatically commit here.
                logger.debug(f"Transaction committed for session {id(session)}")
            except Exception as e:
                # The 'session.begin()' context manager will automatically
                # rollback on any exception.
                logger.error(f"Transaction rolled back for session {id(session)} due to: {e}", exc_info=True)
                raise # Re-raise the exception to be handled by FastAPI's error handlers