"""Centralized accessors for singleton objects stored on ``app.state``.

**Getters** (used by routers): raise 503 when a required dependency is
missing, except ``get_store`` which returns ``None``.

Initialization is handled directly in ``app.py`` via :class:`AsyncExitStack`.
"""

from __future__ import annotations

from collections.abc import AsyncGenerator
from contextlib import AsyncExitStack, asynccontextmanager

from fastapi import FastAPI, HTTPException, Request

from deerflow.runtime import RunManager, StreamBridge


@asynccontextmanager
async def langgraph_runtime(app: FastAPI) -> AsyncGenerator[None, None]:
    """Bootstrap and tear down all LangGraph runtime singletons.

    Usage in ``app.py``::

        async with langgraph_runtime(app):
            yield
    """
    from deerflow.agents.checkpointer.async_provider import make_checkpointer
    from deerflow.runtime import make_store, make_stream_bridge

    async with AsyncExitStack() as stack:
        app.state.stream_bridge = await stack.enter_async_context(make_stream_bridge())
        app.state.checkpointer = await stack.enter_async_context(make_checkpointer())
        app.state.store = await stack.enter_async_context(make_store())
        app.state.run_manager = RunManager()
        yield


# ---------------------------------------------------------------------------
# Getters – called by routers per-request
# ---------------------------------------------------------------------------


def get_stream_bridge(request: Request) -> StreamBridge:
    """Return the global :class:`StreamBridge`, or 503."""
    bridge = getattr(request.app.state, "stream_bridge", None)
    if bridge is None:
        raise HTTPException(status_code=503, detail="Stream bridge not available")
    return bridge


def get_run_manager(request: Request) -> RunManager:
    """Return the global :class:`RunManager`, or 503."""
    mgr = getattr(request.app.state, "run_manager", None)
    if mgr is None:
        raise HTTPException(status_code=503, detail="Run manager not available")
    return mgr


def get_checkpointer(request: Request):
    """Return the global checkpointer, or 503."""
    cp = getattr(request.app.state, "checkpointer", None)
    if cp is None:
        raise HTTPException(status_code=503, detail="Checkpointer not available")
    return cp


def get_store(request: Request):
    """Return the global store (may be ``None`` if not configured)."""
    return getattr(request.app.state, "store", None)