"""TenantHostMiddleware——按 Host 头解析租户的纯 ASGI 中间件(Task 7)。

为什么必须是纯 ASGI 类而不是 ``@app.middleware("http")``(前序审查实证过
的坑): 那条路走 BaseHTTPMiddleware,只跑 http scope——WebSocket 请求会
整个绕过租户解析落进 routes/runtime.py 的兜底,租户 A 的 WS 流量静默写进
租户 B 的库(串库不崩溃,极难发现)。本类自己分发 http 与 websocket 两种
scope type,两条路都先过租户解析。

行为:
- scope 非 http/websocket(lifespan 等)原样放行;
- path 精确等于 ``/health`` 豁免(部署健康检查 ``curl 127.0.0.1:8018``
  /health,Host 是 IP:端口必然未知;精确匹配,``/healthxxx`` 不豁免);
- Host 头 → ``registry.resolve_site``: 未知 → http 404 / ws close(1008);
  租户停用 → http 503 中性"服务暂停"页(不暴露租户信息)/ ws close(1013);
- 解析成功把 tenant/site 写进 ``scope["state"]``——Request/WebSocket.state
  与 scope["state"] 共享同一 dict(setdefault 保证),routes 的 get_runtime
  即读到本中间件写入的 runtime。

Registry 延迟取: ``add_middleware`` 实例化时 lifespan 还没跑、
``app.state.registry`` 未挂,构造期拿不到——从 ``scope["app"].state``
逐请求取(Starlette 在中间件栈外层保证 scope 带 app)。
"""
from starlette.responses import HTMLResponse, PlainTextResponse
from starlette.types import ASGIApp, Receive, Scope, Send

# 归一复用 registry 的私有实现——同一包内单一事实源,中间件与域名索引
# 的建法永不漂移(resolve_site 内部也会再归一次,双保险无害)
from app.platform.registry import (
    TenantDisabledError,
    UnknownTenantError,
    _normalize_host,
)

# 中性"服务暂停"页: 不暴露租户 slug/域名/停用原因(可能是欠费等敏感信息)
PAUSE_PAGE = (
    "<!DOCTYPE html><html lang=\"zh-CN\"><head><meta charset=\"utf-8\">"
    "<title>服务暂停</title></head>"
    "<body style=\"font-family:system-ui,sans-serif;text-align:center;"
    "padding:4rem 1rem;color:#333;\">"
    "<p style=\"font-size:1.1rem;\">服务暂停维护中，请稍后再试。</p>"
    "</body></html>"
)


def _host_from_scope(scope: Scope) -> str:
    """ASGI headers(小写 bytes 键值对)里的 host → str 并归一。"""
    for key, value in scope.get("headers") or []:
        if key == b"host":
            return _normalize_host(value.decode("latin-1"))
    return ""


async def _close_ws(receive: Receive, send: Send, code: int, reason: str) -> None:
    """以 close 代 accept 拒绝 WS(ASGI 规范序列: 先收到 websocket.connect,
    再回 websocket.close)。reason 中性,不带租户信息。

    客户端在握手期间放弃时收到的首个事件是 websocket.disconnect 而非
    connect——对端已撤,close 送达不了,直接 return。receive 本身抛异常
    (传输层断)则向上传播,由外层 ServerErrorMiddleware 记日志:拒绝路径
    无任何已建立状态可留,无需也不应再兜一层。"""
    event = await receive()
    if event["type"] == "websocket.disconnect":
        return
    await send({"type": "websocket.close", "code": code, "reason": reason})


class TenantHostMiddleware:
    """纯 ASGI 租户路由中间件(设计动机见模块 docstring)。"""

    def __init__(self, app: ASGIApp) -> None:
        self.app = app

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        if scope["type"] not in ("http", "websocket"):
            return await self.app(scope, receive, send)
        if scope.get("path") == "/health":
            return await self.app(scope, receive, send)

        registry = getattr(scope["app"].state, "registry", None)
        if registry is None:
            raise RuntimeError(
                "app.state.registry 未挂载——TenantHostMiddleware 需要 "
                "lifespan(或测试注入缝)先加载 TenantRegistry")

        try:
            runtime, site = await registry.resolve_site(_host_from_scope(scope))
        except UnknownTenantError:
            if scope["type"] == "websocket":
                await _close_ws(receive, send, 1008, "unknown host")
            else:
                await PlainTextResponse("Not Found", status_code=404)(
                    scope, receive, send)
            return
        except TenantDisabledError:
            if scope["type"] == "websocket":
                await _close_ws(receive, send, 1013, "service paused")
            else:
                await HTMLResponse(PAUSE_PAGE, status_code=503)(
                    scope, receive, send)
            return

        state = scope.setdefault("state", {})
        state["tenant"] = runtime
        state["site"] = site
        await self.app(scope, receive, send)