"""
Database engine + session management.

Stage 1 scope: users / conversations / messages only.
Long-term memory tables (memories, memory_versions) are introduced in
Stage 4 — do not add them here early, per the "don't over-engineer the
first version" rule.
"""
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, declarative_base

from app.config import settings

connect_args = {"check_same_thread": False} if settings.database_url.startswith("sqlite") else {}

engine = create_engine(settings.database_url, connect_args=connect_args)
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

Base = declarative_base()


def get_db():
    """FastAPI dependency that yields a request-scoped DB session."""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()