import time


class TimingMiddleware:
    """Record server-side request time, mirroring the original app.

    Sets ``request.start_time`` before the view runs so views can report
    elapsed time, and exposes the total duration as a response header.
    """

    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        started = time.perf_counter()
        request.start_time = started
        response = self.get_response(request)
        response["X-Server-Time-Ms"] = f"{(time.perf_counter() - started) * 1000:.1f}"
        return response