from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, DeclarativeBase
from sqlalchemy import text

"""
Database utilities and configuration.  This module defines the SQLAlchemy
engine, session factory and base class for models.  It also contains a
lightweight migration helper used to evolve the schema over time.  The
`ensure_sources_column` helper adds a new `sources_json` column to the
`chat_messages` table if it does not already exist.  This is required
for persisting citation sources alongside assistant messages.

The migration uses SQLite's `ALTER TABLE` syntax and therefore should
only run once on startup.  It is safe to call repeatedly: when the
column already exists, the function will simply no‑op.
"""

DATABASE_URL = "sqlite:///./backend/app.db"

engine = create_engine(
    DATABASE_URL, connect_args={"check_same_thread": False}
)

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

class Base(DeclarativeBase):
    pass


def ensure_sources_column(engine):
    try:
        with engine.connect() as conn:
            cols = [row[1] for row in conn.execute(text("PRAGMA table_info(chat_messages)"))]
            if "sources_json" not in cols:
                conn.execute(text("ALTER TABLE chat_messages ADD COLUMN sources_json TEXT DEFAULT '[]'"))
    except Exception as e:
        print("[db] ensure_sources_column error:", e)