backend/app/database.py

"""Async SQLAlchemy engine and session management."""

from collections.abc import AsyncGenerator
from pathlib import Path

from sqlalchemy import event
from sqlalchemy.ext.asyncio import (
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)
from sqlalchemy.orm import DeclarativeBase

from app.config import get_settings

settings = get_settings()
_is_sqlite = settings.database_url.startswith("sqlite")

# Ensure the data directory exists for SQLite
if _is_sqlite:
    db_path = settings.database_url.split("///")[-1]
    Path(db_path).parent.mkdir(parents=True, exist_ok=True)

engine = create_async_engine(
    settings.database_url,
    echo=False,
    future=True,
    # Wait for a competing writer instead of failing instantly. Background
    # tasks (such as conversation summarization) can briefly hold a write
    # lock, and Windows enforces SQLite locking more strictly than Linux.
    connect_args={"timeout": 30} if _is_sqlite else {},
)

if _is_sqlite:

    @event.listens_for(engine.sync_engine, "connect")
    def _sqlite_pragmas(dbapi_connection, connection_record) -> None:
        cursor = dbapi_connection.cursor()
        cursor.execute("PRAGMA busy_timeout=30000")
        cursor.execute("PRAGMA foreign_keys=ON")
        cursor.close()

AsyncSessionLocal = async_sessionmaker(
    bind=engine,
    class_=AsyncSession,
    expire_on_commit=False,
    autoflush=False,
)


class Base(DeclarativeBase):
    """Declarative base for all ORM models."""


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency that yields a database session."""
    async with AsyncSessionLocal() as session:
        yield session


async def init_db() -> None:
    """Create tables on startup (a migration tool can replace this later)."""
    from app import models  # noqa: F401  (register models with the metadata)

    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)