from collections.abc import Generator
from typing import Any, cast

from sqlalchemy import CursorResult, Engine, create_engine
from sqlalchemy.engine import Result
from sqlalchemy.orm import Session

from modelforge_api.persistence.runtime_engine import register_application_engine
from modelforge_api.settings import get_settings


def rows_affected(result: Result[Any]) -> int:
    """How many rows a DML statement actually changed.

    `Session.execute` is typed as returning `Result`, which carries no `rowcount`; a DML statement
    always returns a `CursorResult`, which does. SQLAlchemy 2.0.52 narrowed that return type, so
    reading `.rowcount` directly stopped type-checking — while continuing to work at runtime.

    The cast is where that knowledge lives, once, rather than at ten call sites. It matters more
    than it looks: every single-use claim in the platform is a conditional UPDATE whose row count
    decides the winner, and that is what makes enrolment tokens and lifecycle claims atomic instead
    of merely usually-correct.
    """

    return cast("CursorResult[Any]", result).rowcount


def build_engine(database_url: str | None = None) -> Engine:
    url = database_url or get_settings().database_url
    return register_application_engine(create_engine(url, pool_pre_ping=True))


engine = build_engine()


def get_session() -> Generator[Session, None, None]:
    with Session(engine) as session:
        yield session