app/database.py

# database.py
# Database connection setup
# Supports both SQLite (local) and PostgreSQL (production/Supabase)

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
import os

# Get database URL from environment variable
# If not set, fall back to SQLite for local development
DATABASE_URL = os.getenv(
    "DATABASE_URL",
    "sqlite:///./shoptracker.db"
)

# PostgreSQL needs different connect_args than SQLite
if DATABASE_URL.startswith("sqlite"):
    engine = create_engine(
        DATABASE_URL,
        connect_args={"check_same_thread": False}
    )
else:
    engine = create_engine(DATABASE_URL)

# Session factory — used in all API routes
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

# Base class for all database models
Base = declarative_base()

# Dependency — used in FastAPI route functions
def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()