"""Async SQLAlchemy database engine and session management."""
from collections.abc import AsyncGenerator

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

from src.backend.config import settings

_IS_SQLITE = settings.database_url.startswith("sqlite")

# Create async engine. MySQL gets a connection pool; SQLite (local file of the
# Windows package) does not accept pool_size/max_overflow/pool_recycle.
if _IS_SQLITE:
    engine = create_async_engine(settings.database_url, echo=False)

    @event.listens_for(engine.sync_engine, "connect")
    def _sqlite_pragmas(dbapi_connection, _connection_record) -> None:
        """Per-connection PRAGMAs: SQLite ignores FKs unless asked, and WAL +
        busy_timeout let the web, vision and backend threads share the file."""
        cursor = dbapi_connection.cursor()
        cursor.execute("PRAGMA foreign_keys=ON")
        cursor.execute("PRAGMA journal_mode=WAL")
        cursor.execute("PRAGMA busy_timeout=5000")
        cursor.close()
else:
    engine = create_async_engine(
        settings.database_url,
        echo=False,
        pool_size=10,
        max_overflow=20,
        pool_recycle=3600,
    )

# Session factory
async_session_factory = async_sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False,
)


class Base(DeclarativeBase):
    """Base class for all SQLAlchemy models."""
    pass


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """Dependency for FastAPI - yields an async database session."""
    async with async_session_factory() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()


async def init_db() -> None:
    """Create all tables (dev only - use Alembic in production)."""
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)