"""Database engine, sessions, and FastAPI dependency."""

from collections.abc import Iterator
from pathlib import Path

from sqlalchemy import Engine
from sqlmodel import Session, SQLModel, create_engine

from .settings import settings

_engine: Engine | None = None


def _engine_kwargs(url: str) -> dict:
    if url.startswith("sqlite"):
        # FastAPI runs sync endpoints in a threadpool; connections are shared
        # across threads, so defer the same-thread check. File-based SQLite
        # needs an existing parent dir (SQLite won't create it).
        return {"connect_args": {"check_same_thread": False}}
    return {}


def get_engine(url: str | None = None) -> Engine:
    """Process-wide engine singleton (override URL in tests via settings)."""
    global _engine
    if _engine is None:
        url = url or settings.database_url
        if url.startswith("sqlite:///") and not url.startswith("sqlite:///:memory:"):
            Path(url.removeprefix("sqlite:///")).parent.mkdir(parents=True, exist_ok=True)
        _engine = create_engine(url, **_engine_kwargs(url))
    return _engine


def reset_engine() -> None:
    """Drop the cached engine (used by the test suite between DB targets)."""
    global _engine
    if _engine is not None:
        _engine.dispose()
        _engine = None


def get_session() -> Iterator[Session]:
    with Session(get_engine()) as session:
        yield session


def create_all(url: str | None = None) -> None:
    """Create tables directly (dev convenience; migrations own prod schema)."""
    SQLModel.metadata.create_all(get_engine(url))