"""请求上下文中间件 — request_id 生成/透传 + 结构化访问日志"""
from __future__ import annotations

import logging
import time
import uuid

from starlette.middleware.base import BaseHTTPMiddleware
from starlette.requests import Request

from app.core.logging import request_id_var, user_var

access_log = logging.getLogger("track.access")

# 探针被高频轮询，降级为 DEBUG 避免把有价值的信息淹掉
_QUIET_PATHS = frozenset({"/health", "/health/live", "/health/ready"})


class RequestContextMiddleware(BaseHTTPMiddleware):
    """为每个请求建立可追踪上下文。

    - request_id：优先沿用上游网关传来的 X-Request-ID，实现全链路追踪；
      没有就生成一个。响应头回写该 ID，前端报错时可直接带上，
      运维拿 ID 就能在日志里精确定位到这一次请求。
    - 访问日志：method / path / status / duration_ms / client / user。
    """

    async def dispatch(self, request: Request, call_next):
        request_id = request.headers.get("X-Request-ID") or uuid.uuid4().hex
        # 同时写入 request.state：它由 ASGI scope 承载，作用域比 contextvar 更长。
        # FastAPI 把 Exception 处理器交给 ServerErrorMiddleware（位于本中间件外层），
        # 异常传播到那里时 contextvar 已在 finally 中被重置，只有 state 还留着 ID。
        request.state.request_id = request_id
        rid_token = request_id_var.set(request_id)
        user_token = user_var.set(None)
        started = time.perf_counter()
        logged = False
        status_code = 500
        try:
            response = await call_next(request)
            status_code = response.status_code
            response.headers["X-Request-ID"] = request_id
            self._log_access(request, status_code, started)
            logged = True
            return response
        finally:
            # 异常路径也要留下访问记录，否则接口 500 时日志里反而没有痕迹
            if not logged:
                self._log_access(request, status_code, started)
            request_id_var.reset(rid_token)
            user_var.reset(user_token)

    def _log_access(self, request: Request, status_code: int, started: float) -> None:
        path = request.url.path
        duration_ms = round((time.perf_counter() - started) * 1000, 1)

        # user 必须从 request.state 取：本中间件在独立 task 中执行，路由内
        # 写入的 contextvar 不会回流到这里（详见 get_current_user 的说明）。
        user = getattr(request.state, "audit_user", None) or user_var.get()

        if status_code >= 500:
            level = logging.ERROR
        elif status_code >= 400:
            level = logging.WARNING
        elif path in _QUIET_PATHS:
            level = logging.DEBUG
        else:
            level = logging.INFO

        access_log.log(
            level,
            "%s %s -> %s (%.1fms)",
            request.method,
            path,
            status_code,
            duration_ms,
            extra={
                "extra_fields": {
                    "method": request.method,
                    "path": path,
                    "status": status_code,
                    "duration_ms": duration_ms,
                    "client": request.client.host if request.client else None,
                    "user": user,
                }
            },
        )