from asyncio import current_task
from typing import Awaitable, Callable

from fastapi import FastAPI
from sqlalchemy.ext.asyncio import (
    AsyncSession,
    async_scoped_session,
    create_async_engine,
)
from sqlalchemy.orm import sessionmaker

from med_backend.db.meta import meta
from med_backend.db.models import load_all_models
from med_backend.services.redis.lifetime import init_redis, shutdown_redis
from med_backend.settings import settings


def _setup_db(app: FastAPI) -> None:  # pragma: no cover
    """
    Creates connection to the database.

    This function creates SQLAlchemy engine instance,
    session_factory for creating sessions
    and stores them in the application's state property.

    :param app: fastAPI application.
    """
    engine = create_async_engine(str(settings.db_url), echo=settings.db_echo)
    session_factory = async_scoped_session(
        sessionmaker(
            engine,
            expire_on_commit=False,
            class_=AsyncSession,
        ),
        scopefunc=current_task,
    )
    app.state.db_engine = engine
    app.state.db_session_factory = session_factory


async def _create_tables() -> None:  # pragma: no cover
    """Populates tables in the database."""
    load_all_models()
    engine = create_async_engine(str(settings.db_url))
    async with engine.begin() as connection:
        await connection.run_sync(meta.create_all)
    await engine.dispose()


def register_startup_event(
    app: FastAPI,
) -> Callable[[], Awaitable[None]]:  # pragma: no cover
    """
    Actions to run on application startup.

    This function uses fastAPI app to store data
    inthe state, such as db_engine.

    :param app: the fastAPI application.
    :return: function that actually performs actions.
    """

    @app.on_event("startup")
    async def _startup() -> None:  # noqa: WPS430
        _setup_db(app)
        await _create_tables()
        init_redis(app)
        pass  # noqa: WPS420

    return _startup


def register_shutdown_event(
    app: FastAPI,
) -> Callable[[], Awaitable[None]]:  # pragma: no cover
    """
    Actions to run on application's shutdown.

    :param app: fastAPI application.
    :return: function that actually performs actions.
    """

    @app.on_event("shutdown")
    async def _shutdown() -> None:  # noqa: WPS430
        await app.state.db_engine.dispose()

        await shutdown_redis(app)
        pass  # noqa: WPS420

    return _shutdown