from collections.abc import Generator

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

from app.core.config import settings


class Base(DeclarativeBase):
    pass


def build_engine(database_url: str):
    connect_args: dict[str, object] = {}
    if database_url.startswith("sqlite"):
        connect_args["check_same_thread"] = False

    return create_engine(database_url, future=True, connect_args=connect_args)


engine = build_engine(settings.database_url)
SessionLocal = sessionmaker(
    bind=engine,
    autoflush=False,
    autocommit=False,
    expire_on_commit=False,
    class_=Session,
)


def get_db() -> Generator[Session, None, None]:
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


def init_db() -> None:
    import app.models  # noqa: F401

    # Keep a lightweight runtime bootstrap for empty local databases so the app
    # can still start before Alembic is wired into every environment.
    Base.metadata.create_all(bind=engine)
    _upgrade_legacy_schema()


def _upgrade_legacy_schema() -> None:
    inspector = inspect(engine)
    table_names = set(inspector.get_table_names())
    if "users" not in table_names:
        return

    existing_columns = {column["name"] for column in inspector.get_columns("users")}
    if "token_version" in existing_columns:
        pass
    else:
        # Keep this compatibility path narrowly scoped for older local databases
        # that predate the Alembic baseline migration.
        with engine.begin() as connection:
            connection.execute(
                text(
                    "ALTER TABLE users "
                    "ADD COLUMN token_version INTEGER NOT NULL DEFAULT 0"
                )
            )

    if "telegram_links" not in table_names:
        Base.metadata.tables["telegram_links"].create(bind=engine)