from sqlalchemy import create_engine, event
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from sqlalchemy.pool import QueuePool
from .settings import settings
from .logging_config import get_logger

logger = get_logger(__name__)

# Database configuration using settings
DATABASE_URL = settings.database_url

# Enhanced engine configuration for enterprise use
engine = create_engine(
    DATABASE_URL,
    poolclass=QueuePool,
    pool_pre_ping=True,  # Verify connections before using
    pool_recycle=3600,  # Recycle connections after 1 hour
    pool_size=10,  # Number of connections to maintain
    max_overflow=20,  # Additional connections beyond pool_size
    echo=settings.is_development,  # Log SQL queries in development
    future=True,  # Use SQLAlchemy 2.0 style
    connect_args={
        "charset": "utf8mb4",
        "connect_timeout": 10
    }
)

# Event listeners for connection pool monitoring
@event.listens_for(engine, "connect")
def set_sqlite_pragma(dbapi_conn, connection_record):
    """Set connection-level settings"""
    logger.debug("New database connection established")

@event.listens_for(engine, "checkout")
def receive_checkout(dbapi_conn, connection_record, connection_proxy):
    """Log connection checkout"""
    logger.debug("Connection checked out from pool")

@event.listens_for(engine, "checkin")
def receive_checkin(dbapi_conn, connection_record):
    """Log connection checkin"""
    logger.debug("Connection returned to pool")

SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

Base = declarative_base()

# Dependency to get DB session
def get_db():
    """
    Dependency for getting database session.
    Automatically handles session lifecycle.
    """
    db = SessionLocal()
    try:
        yield db
    except Exception:
        db.rollback()
        raise
    finally:
        db.close()