"""Database engine & session factory (PostgreSQL 17 + pgvector).

The engine is created lazily: importing this module never opens a
connection, so the app boots (and ``/api/health`` reports) even when the
database is momentarily unavailable.
"""
from __future__ import annotations

from collections.abc import Generator

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

from app.config import get_settings


class Base(DeclarativeBase):
    pass


engine = create_engine(get_settings().database_url, pool_pre_ping=True, future=True)
SessionLocal = sessionmaker(bind=engine, autoflush=False, expire_on_commit=False, future=True)


def get_db() -> Generator[Session, None, None]:
    """FastAPI dependency yielding a database session."""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


def db_available() -> bool:
    """Cheap liveness probe used by ``/api/health``."""
    try:
        with engine.connect() as conn:
            conn.execute(text("SELECT 1"))
        return True
    except Exception:
        return False