from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from .config import settings

# Get the database URL from settings (defaults to SQLite)
SQLALCHEMY_DATABASE_URL = settings.DATABASE_URL

# Create the SQLAlchemy engine. 
# connect_args is only needed for SQLite to handle concurrent access.
engine = create_engine(
    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
)

# Create a configured "Session" class
# expire_on_commit=False prevents objects from being detached after commit
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

# Base class for the data models (models.py will inherit from this)
Base = declarative_base()

# Dependency: Get Database Session
def get_db():
    """
    Dependency injection function to provide a database session 
    to FastAPI endpoints (routers).
    """
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

# Note: Remember to call Base.metadata.create_all(bind=engine) in main.py 
# or use migrations (Alembic) to create tables once models.py is ready.