"""ASGI middleware: request id, access log, metrics, /v1 path alias."""

from __future__ import annotations

import time
from collections.abc import Awaitable, Callable

from fastapi import FastAPI, Request, Response
from starlette.middleware.base import BaseHTTPMiddleware

from packages.shared.context import bind_context, new_request_id, reset_context
from packages.shared.logging import get_logger
from packages.shared.observability import HTTP_LATENCY, HTTP_REQUESTS, current_trace_id

REQUEST_ID_HEADER = "X-Request-Id"

logger = get_logger(__name__)


class RequestContextMiddleware(BaseHTTPMiddleware):
    """Bind request/trace ids, emit the access log, and record HTTP metrics."""

    async def dispatch(
        self, request: Request, call_next: Callable[[Request], Awaitable[Response]]
    ) -> Response:
        request_id = request.headers.get(REQUEST_ID_HEADER) or new_request_id()
        tokens = bind_context(request_id=request_id, trace_id=current_trace_id())
        started = time.perf_counter()
        status_code = 500
        try:
            response = await call_next(request)
            status_code = response.status_code
            response.headers[REQUEST_ID_HEADER] = request_id
            return response
        finally:
            elapsed = time.perf_counter() - started
            route = _route_template(request)
            HTTP_REQUESTS.labels(request.method, route, str(status_code)).inc()
            HTTP_LATENCY.labels(request.method, route).observe(elapsed)
            logger.info(
                "http_request",
                method=request.method,
                route=route,
                status=status_code,
                duration_ms=round(elapsed * 1000, 2),
            )
            reset_context(tokens)


def _route_template(request: Request) -> str:
    route = request.scope.get("route")
    path = getattr(route, "path", None)
    return str(path) if path else request.url.path


def install_version_alias(app: FastAPI, api_prefix: str) -> None:
    """Accept ``/v1/...`` as an alias of ``/api/v1/...``.

    架构文档 §9.1 fixes the base path at ``/api/v1``; several internal specs and
    smoke scripts refer to ``/v1/...``. Rewriting at the ASGI scope keeps a
    single set of route definitions and one OpenAPI document.
    """
    legacy_prefix = "/v1"
    if not api_prefix.endswith(legacy_prefix):
        return

    @app.middleware("http")
    async def _rewrite(
        request: Request, call_next: Callable[[Request], Awaitable[Response]]
    ) -> Response:
        path = request.scope.get("path", "")
        if path == legacy_prefix or path.startswith(legacy_prefix + "/"):
            request.scope["path"] = api_prefix + path[len(legacy_prefix) :]
        return await call_next(request)