"""Per-request trace context with a bounded, non-secret public identifier."""

from __future__ import annotations

import uuid
from collections.abc import Awaitable, Callable

from fastapi import Request, Response

REQUEST_ID_HEADER = "x-request-id"
type CallNext = Callable[[Request], Awaitable[Response]]


def _request_id(value: str | None) -> str:
    if value is not None:
        try:
            return str(uuid.UUID(value))
        except (ValueError, AttributeError):
            pass
    return str(uuid.uuid4())


async def trace_request(request: Request, call_next: CallNext) -> Response:
    """Attach a UUID trace ID and return it without trusting arbitrary input."""

    trace_id = _request_id(request.headers.get(REQUEST_ID_HEADER))
    request.state.trace_id = trace_id
    response = await call_next(request)
    response.headers[REQUEST_ID_HEADER] = trace_id
    return response