"""
MeshBay Hub — async SQLAlchemy engine and session factory.

DATABASE_URL env var controls which DB is used:
  Production:  postgresql+asyncpg://user:pass@localhost/meshbay_hub
  Tests:       sqlite+aiosqlite:///:memory:   (default if not set)
"""

import os
from collections.abc import AsyncGenerator

from sqlalchemy.ext.asyncio import (
    AsyncEngine,
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)

from meshbay_hub.db.models import Base

_DEFAULT_URL = "sqlite+aiosqlite:///:memory:"

def _database_url() -> str:
    return os.environ.get("MESHBAY_DATABASE_URL", _DEFAULT_URL)

# Module-level engine and session factory (initialised in lifespan)
_engine: AsyncEngine | None = None
_session_factory: async_sessionmaker[AsyncSession] | None = None


def get_engine() -> AsyncEngine:
    if _engine is None:
        raise RuntimeError("DB engine not initialised — call init_db() first")
    return _engine


def get_session_factory() -> async_sessionmaker[AsyncSession]:
    if _session_factory is None:
        raise RuntimeError("DB not initialised — call init_db() first")
    return _session_factory


async def init_db(url: str | None = None) -> AsyncEngine:
    """Create engine, session factory, and all tables (idempotent)."""
    global _engine, _session_factory

    db_url = url or _database_url()
    connect_args = {}
    if db_url.startswith("sqlite"):
        connect_args["check_same_thread"] = False

    _engine = create_async_engine(
        db_url,
        echo=False,
        connect_args=connect_args,
    )
    _session_factory = async_sessionmaker(
        _engine, expire_on_commit=False, class_=AsyncSession)

    async with _engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)

    return _engine


async def close_db() -> None:
    global _engine, _session_factory
    if _engine:
        await _engine.dispose()
        _engine = None
        _session_factory = None


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency — yields an async DB session."""
    factory = get_session_factory()
    async with factory() as session:
        yield session