"""Database engine/session wiring. SQLite by default (zero setup), Postgres-ready via DATABASE_URL.

The engine/session factory is process-global and (re)built by `configure()`, so tests can point it
at a temporary database before creating the app.
"""

from __future__ import annotations

import os
from collections.abc import Iterator

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

DEFAULT_URL = "sqlite:///./ams.db"


class Base(DeclarativeBase):
    pass


_engine = None
_SessionLocal: sessionmaker | None = None


def configure(url: str | None = None) -> None:
    global _engine, _SessionLocal
    url = url or os.environ.get("DATABASE_URL", DEFAULT_URL)
    connect_args = {"check_same_thread": False} if url.startswith("sqlite") else {}
    _engine = create_engine(url, connect_args=connect_args, future=True)
    _SessionLocal = sessionmaker(bind=_engine, autoflush=False, expire_on_commit=False, class_=Session)


def init_db() -> None:
    from . import models  # noqa: F401  - register mappers before create_all
    if _engine is None:
        configure()
    Base.metadata.create_all(_engine)


def get_session() -> Session:
    if _SessionLocal is None:
        configure()
    return _SessionLocal()


def get_db() -> Iterator[Session]:
    """FastAPI dependency yielding a request-scoped session."""
    db = get_session()
    try:
        yield db
    finally:
        db.close()