"""Per-request correlation id (ADR-0008, ADR-0011).

Every request gets a `request_id`: reused from an incoming `X-Request-Id` if
the caller supplied one, otherwise generated. It is bound into structlog's
contextvars so every log line emitted while handling the request carries it,
stored on `request.state` for exception handlers, and echoed back in the
response header.
"""

import uuid
from collections.abc import Awaitable, Callable
from typing import override

import structlog
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.requests import Request
from starlette.responses import Response

_HEADER = "X-Request-Id"


class RequestIdMiddleware(BaseHTTPMiddleware):
    @override
    async def dispatch(
        self, request: Request, call_next: Callable[[Request], Awaitable[Response]]
    ) -> Response:
        request_id = request.headers.get(_HEADER) or str(uuid.uuid4())
        request.state.request_id = request_id

        structlog.contextvars.clear_contextvars()
        structlog.contextvars.bind_contextvars(request_id=request_id)
        try:
            response = await call_next(request)
        finally:
            structlog.contextvars.clear_contextvars()

        response.headers[_HEADER] = request_id
        return response