"""SQLAlchemy engine, session factory, and FastAPI dependency."""

import os

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, Session

DATABASE_URL = os.getenv(
    "DATABASE_URL",
    "postgresql://postgres:postgres@localhost:5432/emojinize",
)

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


def get_db() -> Session:
    """
    Yield a database session for a single request, then close it.

    FastAPI injects this as a dependency via Depends(get_db).
    The session is always closed even if the handler raises an exception.

    Yields:
        An active SQLAlchemy Session bound to the configured DATABASE_URL.
    """
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()