"""request_id 关联中间件（ARCH §9.3 / CLAUDE.md）。

每请求生成/透传 request_id，绑入 structlog contextvars，并回写响应头，
错误信封也带上同一 id，便于端到端 grep。
"""

from __future__ import annotations

import uuid
from collections.abc import Awaitable, Callable

import structlog
from starlette.requests import Request
from starlette.responses import Response

REQUEST_ID_HEADER = "x-request-id"


async def request_id_middleware(
    request: Request, call_next: Callable[[Request], Awaitable[Response]]
) -> Response:
    request_id = request.headers.get(REQUEST_ID_HEADER) or uuid.uuid4().hex
    structlog.contextvars.clear_contextvars()
    structlog.contextvars.bind_contextvars(request_id=request_id)
    request.state.request_id = request_id
    response = await call_next(request)
    response.headers[REQUEST_ID_HEADER] = request_id
    return response